Arctic Sea Ice : Forum

Cryosphere => Arctic sea ice => Topic started by: Jim Hunt on May 28, 2019, 10:02:37 AM

Title: Basic questions and discussions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:02:37 AM
Further to one (https://forum.arctic-sea-ice.net/index.php/topic,2707.msg201623) or two (https://forum.arctic-sea-ice.net/index.php/topic,143.msg201340.html#msg201340) recent discussions, here is a place to discuss the basic physics of freezing and melting sea ice.

Here are my own helpful hints on that thorny topic (amongst other things):

http://GreatWhiteCon.info/resources/arctic-sea-ice-explanations/
Title: Re: Basic questions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:05:21 AM
With dramatic loss of old thick sea ice since 2010, I would expect that PIOMAS Sept. minimum would show stronger downward trend for 2010-2019, but while the long term trend is obvious, the last 10 years have been fairly flat.  Why doesn't loss of old thick ice show up more in PIOMAS Sept. minimum volume?
Title: Re: Basic questions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:06:44 AM
Why doesn't loss of old thick ice show up more in PIOMAS Sept. minimum volume?

Because thermodynamics means the new ice grows to 2 meters plus thick across the Arctic Basin over every winter?

See the "Slow Transition" thread (https://forum.arctic-sea-ice.net/index.php/topic,933) for more details.
Title: Re: Basic questions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:07:25 AM
RE #1866 "Because thermodynamics means the new ice grows to 2 meters plus thick across the Arctic Basin over every winter?"

   But that 2 meter new ice growth happens with or without old thick ice.  So it seems that a year with less returning old thick ice from previous year + summer freezing/thickening would result in less volume than an earlier year that had more returning old thick ice and gets the same amount of  summer freezing/thickening.

   The only way I can figure it is that with lower portion of old thick ice, the young ice that replaces it allows faster thickening.  Perhaps the thinner ice cover over water allows more heat loss and thus more thickening, whereas old thick ice is a better insulator and is less dynamic.
Title: Re: Basic questions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:08:00 AM
   But that 2 meter new ice growth happens with or without old thick ice.  So it seems that a year with less returning old thick ice from previous year + summer freezing/thickening would result in less volume than an earlier year that had more returning old thick ice and gets the same amount of  summer freezing/thickening.
And indeed that has been the behavior. When old ice is lost, it is replaced with FYI and the result is a lower winter maximum volume trend. However the winter maximum also depends on the preceding summer minimum and on the effectiveness of autumn freezing. A look at the attached graph (day 120) shows how winter maximum volume has continued on a downward trend, with winter 2017 having an extreme record low. It also shows the correlation between summer minimum (day 260) and the following winter volume. The summer minimum result depends more heavily on weather and is more volatile.

Note: the data includes CAB, Beaufort, Chukchi, ESS, Laptev, Kara, CAA, Greenland Sea - the regions where MYI actually exists.

Note 2: do read the "slow transition" thread, very interesting.

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=143.0;attach=121348;image)
Title: Re: Basic questions about melting physics
Post by: Jim Hunt on May 28, 2019, 10:08:32 AM
Thick ice (of any age - rafting, etc. can make thick year old ice) will not grow 2 meters thicker during the winter when nearby thin ice will.  Attached chart shows an example for lake ice - how it grows less as thickness increases.  Ice, basically, is an insulator.

Decades ago, with much of the Arctic covered in MYI (multiyear ice), there was less volume increase in the central Arctic than during recent winters.

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=143.0;attach=121349;image)
Title: Re: Basic questions about melting physics
Post by: b_lumenkraft on May 28, 2019, 10:30:29 AM
Good move Jim!
Title: Re: Basic questions about melting physics
Post by: Flocke on May 28, 2019, 11:31:40 AM
Ice, basically, is an insulator.

Maybe depending on how you define insulator. Ice has a thermal conductivity of around 2.25 W/mK, water only 0.56 W/mK (both temperature dependant). The difference seems to be the missing convection in ice.
Title: Re: Basic questions about melting physics
Post by: Archimid on May 28, 2019, 01:32:01 PM
Quote
With dramatic loss of old thick sea ice since 2010, I would expect that PIOMAS Sept. minimum would show stronger downward trend for 2010-2019, but while the long term trend is obvious, the last 10 years have been fairly flat.  Why doesn't loss of old thick ice show up more in PIOMAS Sept. minimum volume?


The attached graph shows yearly volume gain and losses calculated from PIOMAS. After 2007 there is a significant increase in losses, but there is also a significant increase in gains. The increase in losses have many causes,  thinner ice being one of them. That's one way that the loss of thick ice shows.

I think the gains in volume are mostly explained by the loss of thick multiyear ice. That's where it really shows. Like Jim said and you correctly explained, thin ice grows to 2 meters very fast relative to ice growth beyond 2 meters.

See Lebedev formula:

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1611.0;attach=88074;image)

The loss of thick ice implies there is much more thin ice, and when there is thin ice volume increases much faster.

Before I finish, I would like to echo Jim and Oren. Read the slow transition thread.
Title: Re: Basic questions about melting physics
Post by: interstitial on May 29, 2019, 11:23:32 AM
I am not certain I have calculations right so if I don’t let me know.


On the molecular scale freezing is an ordered stacking of water molecules so it makes sense that putting ions in the way makes that harder. On the macro scale we see evidence of that when the freezing point decreases.


It is common to see -1.8 C as freezing point of sea water but it is a bit more complicated. -1.8C corresponds to 29.52 g of salts/kg seawater. Molar ratios of  ions are listed below for 35g solute/kg seawater


0.546 moles Cl-
0.469 moles Na+
0.053 moles Mg2+
0.028 moles SO42-
0.0103 moles Ca2+
0.0102 moles K+


Anyway salinity in the artic near the surface varies from about 26 g of salts/kg seawater with a freezing point of -1.58C to 36 g of salts/kg seawater with a freezing point of -2.21C. For most purposes -1.8C is good enough.


But that is not really how sea ice freezes it starts at the temperature associated with the salinity of the water but the ice is nearly pure water. It rejects the salt when it freezes this increases the salinity of the water. So the water has to get a little bit colder to freeze the next bit. This process continues until the salty water gets trapped in ice. Eventually the last of the water freezes at about -21C.  This is first year Ice. It has pockets with high salt concentrations in it. Some of the pockets even most may not of frozen solid.


When the temperature climbs above -21C the pockets of high salt concentration melt first. The temperature is still too low to melt the pure ice.  Since Ice melts at the solid to liquid (or solid to gas interface but that is not relevant here) interface and as the salty water is in contact with pure ice and gets a little bit warmer it can melt a little bit more ice. This lowers the salinity and the ice can’t continue to melt until it gets warmer still.


The high concentration salt water can often burrow out of the pure ice before most of the pure ice melts. When the temperature drops again lower concentration salt water freezes inside. This is how multiyear ice is formed each freeze and thaw cycle of salty water can more and more salts out until it is pure ice with no salts. That makes the multiyear ice fresher and more melt resistant.

The melting temperature of the pure multiyear ice is dependent on the salinity of the surrounding liquid. When the pure multiyear ice melts the local salinity drops and the temperature must increase to melt more. That’s another reason it is more resistant to melt than first year ice.



So to succinctly answer the original question the purified ice melts at the temperature determined by the salinity of the surrounding water. That may be higher than -1.8C but it is not 0C.


Freezing point depression
https://en.wikipedia.org/wiki/Freezing-point_depression (https://en.wikipedia.org/wiki/Freezing-point_depression)
 presentation on chemical composition in sea water
https://www.soest.hawaii.edu/oceanography/courses/OCN623/Spring%202015/Salinity2015web.pdf
Title: Re: Basic questions about melting physics
Post by: Rich on May 29, 2019, 12:56:38 PM
I am not certain I have calculations right so if I don’t let me know.


On the molecular scale freezing is an ordered stacking of water molecules so it makes sense that putting ions in the way makes that harder. On the macro scale we see evidence of that when the freezing point decreases.


It is common to see -1.8 C as freezing point of sea water but it is a bit more complicated. -1.8C corresponds to 29.52 g of salts/kg seawater. Molar ratios of  ions are listed below for 35g solute/kg seawater


0.546 moles Cl-
0.469 moles Na+
0.053 moles Mg2+
0.028 moles SO42-
0.0103 moles Ca2+
0.0102 moles K+


Anyway salinity in the artic near the surface varies from about 26 g of salts/kg seawater with a freezing point of -1.58C to 36 g of salts/kg seawater with a freezing point of -2.21C. For most purposes -1.8C is good enough.


But that is not really how sea ice freezes it starts at the temperature associated with the salinity of the water but the ice is nearly pure water. It rejects the salt when it freezes this increases the salinity of the water. So the water has to get a little bit colder to freeze the next bit. This process continues until the salty water gets trapped in ice. Eventually the last of the water freezes at about -21C.  This is first year Ice. It has pockets with high salt concentrations in it. Some of the pockets even most may not of frozen solid.


When the temperature climbs above -21C the pockets of high salt concentration melt first. The temperature is still too low to melt the pure ice.  Since Ice melts at the solid to liquid (or solid to gas interface but that is not relevant here) interface and as the salty water is in contact with pure ice and gets a little bit warmer it can melt a little bit more ice. This lowers the salinity and the ice can’t continue to melt until it gets warmer still.


The high concentration salt water can often burrow out of the pure ice before most of the pure ice melts. When the temperature drops again lower concentration salt water freezes inside. This is how multiyear ice is formed each freeze and thaw cycle of salty water can more and more salts out until it is pure ice with no salts. That makes the multiyear ice fresher and more melt resistant.

The melting temperature of the pure multiyear ice is dependent on the salinity of the surrounding liquid. When the pure multiyear ice melts the local salinity drops and the temperature must increase to melt more. That’s another reason it is more resistant to melt than first year ice.



So to succinctly answer the original question the purified ice melts at the temperature determined by the salinity of the surrounding water. That may be higher than -1.8C but it is not 0C.


Freezing point depression
https://en.wikipedia.org/wiki/Freezing-point_depression (https://en.wikipedia.org/wiki/Freezing-point_depression)
 presentation on chemical composition in sea water
https://www.soest.hawaii.edu/oceanography/courses/OCN623/Spring%202015/Salinity2015web.pdf

This doesn't make sense.

Sea water contains H2O molecules and NaCl dissolved in a solution.

When sea water freezes, the hydrogen bonds between the water molecules spread out into a fixed lattice structure and the NaCl falls out of the solution into the enlarged spaces between the hydrogen bonds.

Ice is less dense than liquid water. Fewer molecules in a given volume means more space between molecules for the salt / brine to exit the the lattice structure.

There is no frozen salt water in the Arctic. The ice is like a building made out of water molecules. Just as you would not consider a human inside of a building to be part of the building, a salt molecule inside of an ice lattice is not part of the ice.

The "screws" that hold the ice building together are hydrogen bonds. Weaker than covalent bonds inside the water molecules itself, these are intermolecular attractions between positively charged H and negatively charged O atoms.

To unscrew the connections in the building (melt the ice), it is necessary to apply heat to those H-O-H intermolecular bonds. The presence or absence of salt in the vicinity is irrelevant to the properties of the screws holding the H2O house together.

At 1 atm. of pressure, the house is going to fall apart at 0C.
Title: Re: Basic questions about melting physics
Post by: oren on May 29, 2019, 04:28:45 PM
Rich, at the risk of exposing my ignorance, I think you got it wrong there. At the bottom, the ice is floating is salt water, and will melt below 0C. At the top you may be correct.
Title: Re: Basic questions about melting physics
Post by: Rich on May 29, 2019, 05:12:02 PM
Rich, at the risk of exposing my ignorance, I think you got it wrong there. At the bottom, the ice is floating is salt water, and will melt below 0C. At the top you may be correct.

I said the ice will melt at 0C at 1 atm of pressure. This describes surface conditions.

Under water,  pressure increases and changes the melting point.

Ice at depth in a fresh water lake will also melt at temps below 0C due to increased pressure.
Title: Re: Basic questions about melting physics
Post by: Tor Bejnar on May 29, 2019, 06:39:39 PM
Sorry for the aside, but there can be a problem with
Quote
you would not consider a human inside of a building to be part of the building
   When calculating the energy needs of a building (e.g., heating and A/C), the humans can be a significant component.  (Years ago I did public building energy audits.)

I have no clue, however, about salt water freezing and 'fresh' ice thawing issues.
Title: Re: Basic questions about melting physics
Post by: Observer on May 29, 2019, 07:04:00 PM
Thank you for starting this thread. As someone with less knowledge of the natural sciences than of political (unnatural?) science I have many questions about the behavior of water and ice. I have been reading some threads, mostly concerning extent and current season, for a few years. As my curiosity about the physics of water and aqueous solutions has grown, I joined with the hope of asking questions such as those addressed above. This thread and the information have provided above is much appreciated.
Title: Re: Basic questions about melting physics
Post by: oren on May 29, 2019, 07:15:29 PM
Sorry for the back and forth despite my being a layman on this subject. But: I am talking about ice touching salt water, not at depth but nearly at the surface where pressure change is negligible. It is "known" that salt hastens the melting of ice. In other words lowering the melting point, even if the ice is pure freshwater.
Can some expert step in?  ???
Title: Re: Basic questions about melting physics
Post by: johnm33 on May 29, 2019, 11:54:53 PM
From W.Ds. blog "New sea ice starts from 3 important concurring factors: -1.8 C water, little or no sea waves and colder than -11 C surface temperatures "
http://eh2r.blogspot.com/2016/10/new-sea-ice-starts-from-3-important.html
So away from the shore much colder than-11C probably important.
What's the rate of sublimation from ice at various air temps.? since there can't be an energetic 'free lunch' how much impact does this have on ice formation/cooling.
Title: Re: Basic questions about melting physics
Post by: petm on May 29, 2019, 11:57:06 PM
I'm no expert but I know that it's common practice to throw salt on e.g. roads and sidewalks to melt the ice. Presumably sea ice in contact with sea water at a different salinity would have a melting temperature somewhere between the two. https://phys.org/news/2019-02-salt-doesnt-ice-winter-streets.html
Title: Re: Basic questions about melting physics
Post by: interstitial on May 30, 2019, 03:15:25 AM
Temperature is a measure of kinetic energy of the system. Kinetic energy includes translational rotational and vibrational modes.
Temperature does not consider potential energy of the system.  Potential energy includes the energy of bonding. This include strong bonding like ionic and covalent as well as weaker interactions such as hydrogen bonding, vander wahls interactions and others.
Pure water has a higher potential energy than pure ice. If the system is at equilibrium the water and ice have the same kinetic energy namely temperature. The difference in energy is the potential energy of hydrogen bonding you mentioned.
Salt water has a lower potential energy than pure water because of the interactions between ions and water molecules. This interaction is weaker than h bonding so salt water has a higher potential energy then pure ice.

Potential energy of each system from high to low is pure water, salt water and then pure ice. I am not talking about temperature here just bonding energies. 
The potential energy of the saltwater changes with concentration higher concentrations of ions gives lower potential energy of the system.
the difference in potential energy of a saltwater pure ice system is lower than the potential energy difference between pure water and pure ice. Due to conservation of energy potential energy can be converted from kinetic energy. So the kinetic energy required to melt the saltwater pure ice system is lower than for the pure water pure ice system. In other words saltwater pure ice system melts at a lower temperature than pure water pure ice system.
Title: Re: Basic questions about melting physics
Post by: binntho on May 30, 2019, 07:11:36 AM
I should think that Oren is right - salt at the boundary between ice (even if made from pure water) will lower the melting point of that ice. The salt in the sea water causes the ice to melt at a lower temperature.
Title: Re: Basic questions about melting physics
Post by: binntho on May 30, 2019, 07:16:36 AM
Another thing that I've been thinking about lately, given the discussions re. insolation and melt ponds:

For those familiar with snow and ice, seeing ice melt in direct sunlight even when the air temperature is below zero is not unknown. Ice (and snow) will slowly sublimate directly into vapor in dry air, and sunlight helps this process along.

I've also noticed myself how snow that has lying for some time without melt will still have different surface characteristics depending on whether it has been exposed to direct sunlight. In the shadows, the snow is loose while in direct sunlight it seems to gain a brittle crust.

So my point is: Direct sunlight will cause surface melt and surface changes, even if air temperatures are below zero.
Title: Re: Basic questions about melting physics
Post by: wdmn on May 30, 2019, 07:25:57 AM
This is a question/comment about enthalpy of fusion and albedo. It could probably go elsewhere but fits here too, I think.

Ice at 0 Celsius takes a lot of energy to melt from latent heat.

According to wikipedia, it takes 333.55 kJ of energy to melt 1 kg of ice, but only 83.6 kJ of energy to increase the temperature of 1kg of water by 20 degrees celsius. That means that 333.55 kJ of energy raises the temperature of water ~80 degrees C.

Discussion around decreasing arctic sea ice tends to be about albedo. But doesn't decreasing sea ice also mean an increasing amount of available latent heat to warm the oceans/adjacent land? And what might that mean as we approach <1mk2 of summer sea ice? It seems like it would be simple math to quantify the excess heat going into the exposed ocean, and I wonder if anyone has done that already?

Thanks
Title: Re: Basic questions about melting physics
Post by: binntho on May 30, 2019, 07:50:57 AM
Definitely during summer the latent heat uptake of melting ice keeps the temperature hovering just over the 0 mark as can be seen on the DMI graphs. There are also temperature spikes in autumn when the freezing gets going, with release of latent heat that presumably is lost out through the atmosphere.

On the other hand, the ice insulates the underlying sea from losing too much heat to the atmosphere, so I´m not at all sure what the net result of a more-or-less ice free arctic would be.
Title: Re: Basic questions about melting physics
Post by: wdmn on May 30, 2019, 08:35:50 AM
Thank you. Always something to make things more complex...

But there's got to be some way to think about this numerically. I wonder if anyone's done it? Anyway, I'll give it some more thought.
Title: Re: Basic questions about melting physics
Post by: interstitial on May 30, 2019, 10:18:29 AM
This is a question/comment about enthalpy of fusion and albedo. It could probably go elsewhere but fits here too, I think.

Ice at 0 Celsius takes a lot of energy to melt from latent heat.

According to wikipedia, it takes 333.55 kJ of energy to melt 1 kg of ice, but only 83.6 kJ of energy to increase the temperature of 1kg of water by 20 degrees celsius. That means that 333.55 kJ of energy raises the temperature of water ~80 degrees C.

Discussion around decreasing arctic sea ice tends to be about albedo. But doesn't decreasing sea ice also mean an increasing amount of available latent heat to warm the oceans/adjacent land? And what might that mean as we approach <1mk2 of summer sea ice? It seems like it would be simple math to quantify the excess heat going into the exposed ocean, and I wonder if anyone has done that already?

Thanks


the temperature is kinetic energy and the latent heat of fusion is potential this energy can and readily does converts from one to the other but that doesn't change the total energy of the system.


if you think about the water and ice of the ocean as a system with thorough mixing and no change in energy to or from the system the temperature will be at the freezing point and there will be a fixed amount of ice. Of course the ocean isn't perfectly mixed but it is easier to think about.



Adding energy to the ocean system can decrease the amount of ice in the ocean or increase the temperature. If it is not thouroghly mixed it can do both at the same time at different locations.


So whats really important is the energy imbalance of the system overtime. Solar energy from space can add energy to the system and warm objects emit energy in the infrared to space. Solar energy entering the atmosphere is mostly predictable based on the season. their is some variation of in solar cycles but that is not as significant as the season in the arctic. The amount of energy that an object radiates is a function of material and temperature. The albedo of the atmosphere and ice are harder to predict and control how much energy makes it in and out of the system.   


Yes in general someone has calculated how much energy is tied up in melting ice but it is not very useful as it is a simple calculation of volume of ice melted times the latent heat of fusion. If you can predict energy flow over time it would be relatively straight forward to predict the volume.


On a related note volume numbers are mostly based on models and little on direct measurement. Models can only get better with lots of direct measurement. Only the thinnest of ice can be measured by satellite. Occasionally people go to measure ice thickness but that isn't nearly enough and only produces one data point at a time. Because of this their is large variability in the thickness data from different models. They are working on a system measure thickness from below I believe using sonar but I am not sure.
Title: Re: Basic questions about melting physics
Post by: petm on May 30, 2019, 02:36:54 PM
According to wikipedia, it takes 333.55 kJ of energy to melt 1 kg of ice, but only 83.6 kJ of energy to increase the temperature of 1kg of water by 20 degrees celsius. That means that 333.55 kJ of energy raises the temperature of water ~80 degrees C.

Yes, and once that energy becomes available, what happens to the weather? In vulnerable regions, could some storms mix up to the surface warm Atlantic waters from below the halocline? If so, could this become a positive feedback, further increasing storm intensity and subsequent mixing? And what could be the result of such a feedback on global atmospheric circulation patterns, winter re-freeze, etc.?

At some point, the Arctic will become ice-free year-round. This will very probably require centuries more warming, but no one really knows how long or the path that will take us there.
Title: Re: Basic questions about melting physics
Post by: Glen Koehler on May 30, 2019, 03:28:47 PM
     Simpler framing of the original question makes the answer easier to see.
Original mystery (to me at least) was why wasn't PIOMAS volume decreasing in sync  with loss of old think ice?

    My new dope-slap-forehead observation - winter maximums have declined, but not as much as summer minimums (maxima, minima for those of you who remember 7th grade Latin).  Thus it is clear that winter refreeze has increased along with declining summer minima.  Not enough to fully compensate for increased summer losses, but enough to reduce their impact on winter maxima.
 
   As helpfully pointed out by Oren and others, that is indeed the case.  As to why winter ice gain increases with declining summer minima, two mechanisms are
1) thinner ice is able to increase thickness faster, and
2) ice cover acts as an insulator, thus less insulation means faster cooling in the following fall/winter. 
     There may be other mechanisms in addition to 1 and 2 (changes in cloud cover or wind patterns?).  And within 1 and 2 there are more detailed explanations for how/why they work.

   So nothing new here in this post!  I just thought anybody who was also puzzled by the original question, lack of 1:1 correlation between dramatic loss of older, thick ice, and the more subtle (but consistent trend) of PIOMAS ice volumes would find a bit of catch up and summary useful. 

   Two particularly interesting and useful points that arose -
    a) thick ice does not necessarily mean old ice.  Thinner fractured ice floes are more susceptible to being transported by wind or currents into thicker piles.
   b) salinity differences account for why older ice is more resistant to melt; and younger, saltier ice is less resistant to melt (though not everybody seems to agree about the chemistry at the molecular level).
   
Title: Re: Basic questions about melting physics
Post by: gerontocrat on May 30, 2019, 03:30:08 PM

But there's got to be some way to think about this numerically. I wonder if anyone's done it?
I like this example from the Polar Science Center, which brings in both the overall vast energy quantities involved and a dim light bulb at the micro level.

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
Quote
Perspective: Ice Loss and Energy
It takes energy to melt sea ice. How much energy? The energy required to melt the 16,400 Km3 of ice that are lost every year (1979-2010 average) from April to September as part of the natural annual cycle is about 5 x 1021 Joules. For comparison, the U.S. Energy consumption for 2009 (www.eia.gov/totalenergy) was about 1 x 1020 J. So it takes about the 50 times the annual U.S. energy consumption to melt this much ice every year. This energy comes from the change in the distribution of solar radiation as the earth rotates around the sun.

To melt the additional 280 km3 of sea ice, the amount we have have been losing on an annual basis based on PIOMAS calculations, it takes roughly 8.6 x 1019 J or 86% of U.S. energy consumption.

However, when spread over the area  covered by Arctic sea ice, the additional energy required to melt this much sea ice is actually quite small. It corresponds to about 0.4 Wm-2 . That’s like leaving a very small and dim flashlight bulb continuously burning on every square meter of ice. Tracking down such a small difference in energy is very difficult, and underscores why we need to look at longer time series and consider the uncertainties in our measurements and calculations.
Title: Re: Basic questions about melting physics
Post by: binntho on May 30, 2019, 04:16:06 PM
It's not a simple matter!

       Two particularly interesting and useful points that arose -
    a) thick ice does not necessarily mean old ice.  Thinner fractured ice floes are more susceptible to being transported by wind or currents into thicker piles.
   b) salinity differences account for why older ice is more resistant to melt; and younger, saltier ice is less resistant to melt (though not everybody seems to agree about the chemistry at the molecular level).

I think that a) is a very useful insight, but b) is perhaps not wholly correct. Younger ice will tend to be more porous and even contain pockets of brine, both of which help with faster melting.

And I don't think there is any real disagreement abut the molecular-level chemistry - it's fairly basic after all. But applying molecular-level chemistry to floating sea ice is perhaps a bit more tricky.
Title: Re: Basic questions about melting physics
Post by: LRC1962 on May 30, 2019, 09:57:31 PM
https://nsidc.org/cryosphere/seaice/index.html (https://nsidc.org/cryosphere/seaice/index.html)
Quote
Can you drink melted sea ice?
New ice is usually very salty because it contains concentrated droplets called brine that are trapped in pockets between the ice crystals, and so it would not make good drinking water. As ice ages, the brine eventually drains through the ice, and by the time it becomes multiyear ice, nearly all of the brine is gone. Most multiyear ice is fresh enough that someone could drink its melted water. In fact, multiyear ice often supplies the fresh water needed for polar expeditions. See Salinity and Brine in the Characteristics section for more information.
https://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html (https://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html)
Quote
Fresh water freezes at 0 degrees Celsius (32 degrees Fahrenheit), but the freezing point of sea water varies. For every 5 psu increase in salinity, the freezing point decreases by 0.28 degrees Celsius (0.5 degrees Fahrenheit); thus, in polar regions with an ocean salinity of about 32 psu, the water begins to freeze at -1.8 degrees Celsius (28.8 degrees Fahrenheit). The Arctic Ocean is generally fresher than other oceans, somewhere between 30 and 34 psu, but salinity levels vary by region, and areas with strong river inflow may have even lower salinity.
Title: Re: Basic questions about melting physics
Post by: Glen Koehler on May 31, 2019, 01:59:15 AM
Doing some homework by reading the Slow Transition forum. https://forum.arctic-sea-ice.net/index.php/topic,933, 
    To expedite access to the take home points for others still getting their arms around the original question, here are some selected items from that discussion that provide a plausible explanation.  The quotes are from 2014 and I think they hold up well 5 years later.

1. Chris Reynolds #6  July 2014
"...2007 and 2012 saw massive gains in volume despite delays to the onset of melt. This is because the rate of growth of ice for open water and thin ice is extremely fast. The following graphic is from Thorndike 1975."

(https://imagizer.imageshack.com/v2/320x240q90/921/mohdgL.png)

2. Chris Reynolds #49  July 2014
"…the contention that future April Arctic Ocean volume will be set by ice growing to thermodynamic equilibrium thickness (TET) from September to April, then further volume loss events leading to net thinning of the pack and enabling further increases of melt season losses of volume look unlikely.   Because with a mainly first year ice pack further drops in volume in years like 2012 will be followed by rapid recoveries to the volume implied by the TET around the time of those drops within a few years at most (Tietsche et al)."

3. From Chris Reynolds  Dosbat Blog.  http://dosbat.blogspot.com/2014/07/the-slow-transition.html
    "I am becoming convinced that the approximate levelling of PIOMAS volume over the last few winters is telling us that the pack is becoming dominated by FYI, whose thermodynamic equilibrium thickness is largely setting the peak volume in April."

    "I was persuaded that the loss of MYI represented energy that would then have to go into melting FYI after the MYI had declined. However because FYI regrows in the winter it vents this notional energy. The energy that once went into melting MYI is thus vented into the atmosphere and radiated to space in autumn/winter."
Title: Re: Basic questions about melting physics
Post by: Tor Bejnar on May 31, 2019, 02:35:06 AM
I 'found' this 1991 paper Physical and Dynamic Properties of Sea Ice in the Polar Oceans (https://apps.dtic.mil/dtic/tr/fulltext/u2/a256303.pdf) linked in a 2017 Barneo post (https://forum.arctic-sea-ice.net/index.php/topic,1905.msg108637.html#msg108637).  I've been reading about ice salinity and the various mechanisms that desalinate ice. (40+ pages)
Title: Re: Basic questions about melting physics
Post by: Archimid on May 31, 2019, 02:54:31 AM
Quote
"The energy that once went into melting MYI is thus vented into the atmosphere and radiated to space in autumn/winter."

And that shows as much warmer fall/winter temperatures, and in some cases a delay in freezing until the extra atmospheric and ocean heat is "vented".

See the fall/winter of 2016/17

https://www.climate.gov/news-features/featured-images/2017-arctic-report-card-extreme-fall-warmth-drove-near-record-annual

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Focean.dmi.dk%2Farctic%2Fplots%2FmeanTarchive%2FmeanT_2016.png&hash=ed3bc1964e488b5d83cfae05c243a1bc)

This is where I believe the slow transition theory has the highest chance for failing early.
Title: Re: Basic questions about melting physics
Post by: oren on May 31, 2019, 03:09:42 AM
Doing some homework by reading the Slow Transition forum. https://forum.arctic-sea-ice.net/index.php/topic,933, 
    To expedite access to the take home points for others still getting their arms around the original question, here are some selected items from that discussion that provide a plausible explanation.  The quotes are from 2014 and I think they hold up well 5 years later.
While Chris's theory was brilliant and I think very innovative for its time, the winter of 2016-2017 showed that it was not foolproof. Refreeze was so delayed and autumn temps so high (as noted by Archimid above) that April saw a record low volume in the Arctic Ocean. I cannot manage to recreate Chris's numbers but here's a chart showing PIOMAS volume for the inner basin plus CAA and Greenland Sea for day 120, with 2010-2014's flatline highlighted. The break below 18k km3 clearly shows that the transition may not be as slow as postulated/hoped for - because the FYI may not thicken as much as it used to.
Title: Re: Basic questions about melting physics
Post by: Dharma Rupa on June 02, 2019, 07:27:47 PM
My memory of the slow transition thread is that the main questionmark was the future behavior of water vapor.  My contention at the time, and to this day, is that the Arctic is in transition from a desert climate to a maritime climate.  The Arctic nights are going to get cloudier and lose less heat to space.  I think the transition from desert to maritime has already happened rather abruptly in late December 2015, and we are now simply waiting for enough ice to melt in Summer that it cannot reach thermal equilibrium the following Winter.

Title: Re: Basic questions about melting physics
Post by: Dharma Rupa on June 02, 2019, 07:29:18 PM
Sorry for the back and forth despite my being a layman on this subject. But: I am talking about ice touching salt water, not at depth but nearly at the surface where pressure change is negligible. It is "known" that salt hastens the melting of ice. In other words lowering the melting point, even if the ice is pure freshwater.
Can some expert step in?  ???

How about someone who has made ice cream?
Title: Re: Basic questions about melting physics
Post by: johnm33 on June 02, 2019, 09:47:03 PM
" Salty water freezes at a lower temperature than plain water. But the ice is made of plain water, so it melts at 0 degrees Celsius. Since the ice keeps melting, but the water no longer freezes (because there is only salt water, which doesn't freeze at 0 degrees), the temperature goes down.

The heat gained by the ice as it melts is no longer offset by the heat given up by freezing water (since the water is no longer freezing back onto the ice). The heat gain has to come from somewhere else. It comes from the ice cream and your hands.

The sodium and chlorine in the salt split apart into charged ions, and these ions attract water molecules to form weak chemical bonds.

The resulting compound has a freezing point of -21.1 degrees Celsius (-5.98 degrees Fahrenheit). This is 21.1 degrees colder than ice (37.98 degrees Fahrenheit colder than ice). " from https://sci-toys.com/scitoys/scitoys/thermo/ice_cream/ice_cream.html
So it seems that any windborne salt could 'suck' heat out of the wet surface layer of ice creating I presume a drop of brine at>-0C but cooling the remainder down to a possible -21C but no further effect on saltwater.
Title: Re: Basic questions about melting physics
Post by: SteveMDFP on June 02, 2019, 11:43:56 PM

The resulting compound has a freezing point of -21.1 degrees Celsius (-5.98 degrees Fahrenheit). This is 21.1 degrees colder than ice (37.98 degrees Fahrenheit colder than ice). " from https://sci-toys.com/scitoys/scitoys/thermo/ice_cream/ice_cream.html
So it seems that any windborne salt could 'suck' heat out of the wet surface layer of ice creating I presume a drop of brine at>-0C but cooling the remainder down to a possible -21C but no further effect on saltwater.

Windborne salt?  On the forum somewhere recently it was stated that 2/3 of overall melt is bottom surface melt.  Only 1/3 is top surface.  Salty seawater will melt the bottoms of floes until an equilibrium temp is reached.  Although the freshening of the seawater by melt will slow the process, there's always some mixing of seawater going on, and also conduction of heat from another meter or so down.
Title: Re: Basic questions about melting physics
Post by: Phil. on June 04, 2019, 02:02:19 PM
Temperature is a measure of kinetic energy of the system. Kinetic energy includes translational rotational and vibrational modes.
Temperature does not consider potential energy of the system.  Potential energy includes the energy of bonding. This include strong bonding like ionic and covalent as well as weaker interactions such as hydrogen bonding, vander wahls interactions and others.
Pure water has a higher potential energy than pure ice. If the system is at equilibrium the water and ice have the same kinetic energy namely temperature. The difference in energy is the potential energy of hydrogen bonding you mentioned.
Salt water has a lower potential energy than pure water because of the interactions between ions and water molecules. This interaction is weaker than h bonding so salt water has a higher potential energy then pure ice.

Potential energy of each system from high to low is pure water, salt water and then pure ice. I am not talking about temperature here just bonding energies. 
The potential energy of the saltwater changes with concentration higher concentrations of ions gives lower potential energy of the system.
the difference in potential energy of a saltwater pure ice system is lower than the potential energy difference between pure water and pure ice. Due to conservation of energy potential energy can be converted from kinetic energy. So the kinetic energy required to melt the saltwater pure ice system is lower than for the pure water pure ice system. In other words saltwater pure ice system melts at a lower temperature than pure water pure ice system.

The other important factor in the solutions is entropy which can have a bigger contribution to Free Energy than enthalpy in such mixture.  The 'order' due to hydrogen bonding around the ions being a major contributor in some biological systems the 'order' effects can be the drivers rather than enthalpy differences:  DeltaG=DeltaH-T*DeltaS
Title: Re: Basic questions about melting physics
Post by: Tor Bejnar on July 25, 2019, 05:41:45 PM
There was some discussion on a 'main' thread abut 850 temperatures vs. 2m temperatures.

Towards our mutual understanding of whys and wherefores, I offer the following.  I know extremely little about atmospheric science, so cannot offer (really) anything, but hope those who do will share more, even extensively!

An internet search led me to WeatherPrediction.com (http://www.theweatherprediction.com/habyhints/278/). 
Quote
FORECASTING SURFACE HIGH USING 850-mb TEMP 

METEOROLOGIST JEFF HABY

LIMITATIONS

 Forecasting the surface high using the 850-mb temperature has been a popular forecasting technique. First Iwill go over the limitations of using this method:

 1. Method does not work on cloudy days or days with afternoon precipitation

 2. There is a tendency that temperature will be higher than predicted on days the wind is light and will be lower than predicted on days the wind is strong. This is because the low level wind effectsthe depth of mixing.

 3. Method assumes air is mixed only between the surface and 850 mb. If the air mixes to a height significantly above or below 850 mb the technique will not work accurately.

 4. Method does not account for elevation. High elevation regions have a greater chance of mixing air that is above 850 mb.

 5. Daylight hours effect accuracy. There is a significant difference in daylight hours between the warm and cool season.

 6. Method only works in a barotropic atmosphere. Fronts or differential advection will contaminate technique.

 7. Method does not work well in regions with complex topography or near mesoscale temperature gradients such as coastal areas, very hilly areas, and areas near large lakes.

 The method works best in locations near sea level, in the warm season, on barotropic days, with flat topography, on moderate windy cloud-free days. If any of these conditions are not met then take that into account on the temperature prediction.

THE METHOD

 The method itself is very easy. Method needs to be done on a Skew-T to ensure accuracy. From the morning sounding, note the 850-mb temperature. Take a parcel of air at 850 mb using the 850-mb temperature and bring it dry adiabatically to the surface. The temperature of this parcel after it is brought to the surface will estimate the high temperature for the day.
[minor editing - some words became 'run-on words' when copied]
Title: Re: Basic questions about melting physics
Post by: Rich on July 25, 2019, 06:39:57 PM
Thank you Tor !!
Title: Re: Basic questions about melting physics
Post by: Tor Bejnar on July 25, 2019, 06:40:13 PM
Here is an apparent conflict between physics and 'experience'.
Quote
You do know that there are no "sources" of cold?

Of course there are sources of cold. If I have a glass of warm water and I need a source of cold I just go get some ice and throw it in.
<Snippage>
OK, while creative, not really A Thing.

You don't really have "sources of cold" any more than you have "sources of vaccuum".  What "cold" indicates is a difference in enthalpy - net heat content components of a system, and thanks to the laws of thermodynamics heat will attempt to equilibrate across it - thus your ice cubes melting. 

There wasn't any "cold source" here, just the heat of varying levels being redistributed.

This does bring me to a point which I feel people have been overlooking.  It unfortunately is one for which we probably have the least instrumentation for - net enthalpy of the Arctic ocean and surrounding seas.

*This* will be the key factor in the tipping point.
<<a great deal of material removed - it is basically Arctic-specific.>>

In the northern hemisphere mid-latitudes when a 'cold North wind' blows, it gets colder.  A balloon floating in that cold air physically goes south, so I say the cold air came south too.  The source of that cold air was 'someplace' north of me.  Yes, it is a 'distribution' thing, but in the local sense, it sure seems like there is a 'source'.  The balloon 'came from the north', why can't the 'cold'?  OK: the 'air packet' came from the north, and it happened to be cold.  That air packet is cold because it lost its heat to the heavens [angels, I guess, lug the heat up when taking breaks from harp playing].  So, a source for the air, but not the cold.

(Those drink-cooling ice cubes were clearly made by a 'heat-redistribution machine'.)
How wrong did I go, physicists of the world?
Title: Re: Basic questions about melting physics
Post by: DrTskoul on July 25, 2019, 07:34:30 PM
From a mathematical point of view, similar to a current of "holes" in semiconductors , a current and a source of "cold" for a higher level ( not deep) understanding are perfectly valid as long as one appreciates the simplifying assumptions. For me as a chemical engineer, I can solve the problem and give you the same result regardless the framework.
Title: Re: Basic questions about melting physics
Post by: binntho on July 26, 2019, 07:15:30 AM
Here is an apparent conflict between physics and 'experience'.
Quote
You do know that there are no "sources" of cold?

Of course there are sources of cold. If I have a glass of warm water and I need a source of cold I just go get some ice and throw it in.
<Snippage>
OK, while creative, not really A Thing.

You don't really have "sources of cold" any more than you have "sources of vaccuum".  What "cold" indicates is a difference in enthalpy - net heat content components of a system, and thanks to the laws of thermodynamics heat will attempt to equilibrate across it - thus your ice cubes melting. 

There wasn't any "cold source" here, just the heat of varying levels being redistributed.

This does bring me to a point which I feel people have been overlooking.  It unfortunately is one for which we probably have the least instrumentation for - net enthalpy of the Arctic ocean and surrounding seas.

*This* will be the key factor in the tipping point.
<<a great deal of material removed - it is basically Arctic-specific.>>

In the northern hemisphere mid-latitudes when a 'cold North wind' blows, it gets colder.  A balloon floating in that cold air physically goes south, so I say the cold air came south too.  The source of that cold air was 'someplace' north of me.  Yes, it is a 'distribution' thing, but in the local sense, it sure seems like there is a 'source'.  The balloon 'came from the north', why can't the 'cold'?  OK: the 'air packet' came from the north, and it happened to be cold.  That air packet is cold because it lost its heat to the heavens [angels, I guess, lug the heat up when taking breaks from harp playing].  So, a source for the air, but not the cold.

(Those drink-cooling ice cubes were clearly made by a 'heat-redistribution machine'.)
How wrong did I go, physicists of the world?
In daily parlance, having a "source" of cold is quite normal. Having just had my air-conditioner fixed has made me thankful for that particular source of cold when I'm trying to sleep.

But when talking about larger systems, hemispheric and global weather for example, one has to be clear that  there is never a source of cold, only sources of heat.

I started this whole "source of cold" discussion after reading a post by Archimid about how there were this and that source of cold that could have this and that effect on the Arctic. That was so obviously a wrong way to talk about weather and climate that I had to ask, and he has been strangely reticent in agreeing with the physics.

I also wanted to point out (and perhaps get a little bit closer to the topic of this thread? Edit: Didn't realize that this was a new and more appropriate thread for this sort of thing) that space is a great sucker of warmth, a massive sink of heat, and would be by very far the hugest "source of cold" ever.

And the Arctic, during the winter months, loses massive amounts of heat to space and will continue to do so. Losing summer ice is only going to increase this heat loss, and if there ever is an equitable climate, this heat loss is going to get even bigger, leading to a fall in temperatures elsewhere.

Which all counts as a huge negative feedback, reducing the speed of global warming and generally working to cool the planet down.

Of course, there is another, very potent positive feedback in losing Arctic ice, so an ice-free Arctic ocean will presumably have a significant net effect of warming rather than cooling the planet. But never forget that negative feedback that's going to have it's say as well!

And once all the ice is gone, the positive feedback of losing ice stops. But the negative feedback of losing heat just keeps growing with increasing temperatures. How this will all play out is a total mystery to me, but some people seem to think they've got it all worked out.
Title: Re: Basic questions about melting physics
Post by: bill kapra on August 21, 2019, 01:57:10 AM
Hey folks,

Longtime lurker. Soft condensed matter guy. Just starting to look at sea ice and stumbled across this. FWIW:

Critical behavior of transport in sea ice

Author links open overlay panelK.M.Golden
Show more
https://doi.org/10.1016/j.physb.2003.08.007Get rights and content
Abstract
Geophysical materials such as sea ice, rocks, soils, snow, and glacial ice are composite media with complex, random microstructures. The effective fluid, gas, thermal, and electromagnetic transport properties of these materials play an important role in the large-scale dynamics and behavior of many geophysical systems. A striking feature of such media is that subtle changes in microstructural characteristics can induce changes over many orders of magnitude in the transport properties of the materials, which in turn can have significant large-scale geophysical effects. For example, sea ice, which mediates energy transfer between the ocean and atmosphere, plays a key role in global climate, and serves as an indicator of climatic change, is a porous composite of ice, brine and gases. Relevant length scales range from microns and millimeters for individual brine structures, to centimeters and meters for connected brine channels across floes, to hundreds of kilometers across an ice pack. Sea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a relatively small temperature range. The fluid permeability of sea ice ranges over six orders of magnitude for temperatures between 0°C and −25°C. Moreover, small changes in brine volume fraction around a threshold value of about 5%, corresponding to variations in temperature around a critical point of about −5°C, control an important transition between low and high fluid permeability regimes. Below this critical temperature, the sea ice is effectively impermeable, while for higher temperatures the brine phase becomes connected over macroscopic scales, allowing fluid transport through the ice. This transition has been observed to impact a wide range of phenomena such as surface flooding and snow–ice formation, enhancement of heat transfer due to fluid motion, mixing in the upper ocean, melt pool persistence, surface albedo (ratio of reflected to incident radiation) and other optical properties, growth and nutrient replenishment of algal and bacterial communities living in sea ice, and remote sensing of the sea ice pack from space. Recently, we have shown how continuum percolation theory can be used to understand the critical behavior of fluid transport in sea ice. Here we review this application of percolation theory to sea ice, and briefly discuss electromagnetic transport in sea ice, in particular how the geometry and connectivity of the brine microstructure determine its effective complex permittivity.
Title: Re: Basic questions about melting physics
Post by: nanning on August 21, 2019, 05:34:52 AM
Thanks bill, very interesting abstract.

Being a soft condensed matter guy, you might have some knowledge and understanding to add to the "Sea Ice Melting Affected by Microplastics?"-thread:
https://forum.arctic-sea-ice.net/index.php/topic,2732.msg203438.html#msg203438

(the hyperlink to the abstract/paper is not correct because of the attached "Get")  https://doi.org/10.1016/j.physb.2003.08.007
Title: Re: Basic questions about melting physics
Post by: bill kapra on August 21, 2019, 10:29:41 PM
Thanks for the fix and the reference, Nanning. Fascinating materials problem here!
Title: Re: Basic questions about melting physics
Post by: blumenkraft on August 28, 2019, 10:33:51 PM
Not entirely on topic, but the ice is melting there. (maybe)

Hear physics! Scary sounds from a frozen lake 🔊

Link >> https://www.reddit.com/r/Damnthatsinteresting/comments/cwmpk9/scary_sounds_from_a_frozen_lake/
Title: Re: Basic questions about melting physics
Post by: nanning on August 29, 2019, 05:27:23 AM
Maybe I'm not hearing the special sounds?  :-\

Those sounds are very familiar to me. I thought this is what a clear frozen toplayer does over a larger expanse.

I also remember cracks overtaking you when iceskating on a thin layer, also with great sounds. 8)
They say "cracking ice is trustworthy ice to skate on. If it doesn't make cracking sounds, be very careful".

That guy throwing the icesheet whilst rotating has had some practice I think. I wonder how many sets of dry clothes he used up for that shot, or perhaps the ice is much thicker than the icesheet he's throwing. Icesheets are supposed to be pretty heavy  ;D
Title: Re: Basic questions about melting physics
Post by: binntho on August 29, 2019, 05:42:53 AM
Not entirely on topic, but the ice is melting there. (maybe)

Hear physics! Scary sounds from a frozen lake 🔊

Link >> https://www.reddit.com/r/Damnthatsinteresting/comments/cwmpk9/scary_sounds_from_a_frozen_lake/

I've seen another one (if I remember correctly) where he used a single stone. The lake was very different, in a forested narrow valley.

But anyway, the sound that's so "scary" is the echo of the impact (and subsequent sliding) of the ice. This echo seems to be reverberating from the ice, a bit like the soundbox of a guitar or a violin, and then slowly fading away.

Wonder if there is a free space under the ice, creating the "soundbox" - i've seen such things (i.e. free space under the ice) happen on a lakesize scale, but with much thinner ice.
Title: Re: Basic questions about melting physics
Post by: Feeltheburn on August 30, 2019, 07:51:26 AM
This very interesting discussion regarding the heat losses and gains when ice melts and refreezes got me to thinking about a different heat flow issue involving water: Liquid water and water vapor.

I can't seem to find much in the climate science literature about it, but it is in physics books and an old popular science archive from 1891. Yes, that long ago!

When water evaporates from a body of water, the remaining thermal energy in the water is reduced by the amount of heat required to cause the phase change, or the latent heat of vaporization, which is enormous (540 calories per gram of water). It takes 100 calories to heat water from 0 degrees C to 100 degrees C, but 5-1/2 times more heat to just change liquid water to water vapor at constant temperature. This explains why evaporative coolers are very efficient at lowering air temperature in hot, dry climates.

When water evaporates from the ocean, heat energy (540 cal/gram) is transferred from the water to the water vapor, which then rises up into the upper atmosphere, where it meets extremely cold dry air, forms clouds, and then precipitates as rain or snow. When water vapor turns into water or ice, an enormous amount of heat energy is released into the surrounding upper atmosphere equal to the latent heats of vaporization and fusion.

Thus, there is a constant cooling cycle in which heat energy in the ocean is continuously being transferred to the upper atmosphere, where extremely cool rarified air absorbs this energy, causing water to precipitate and return to the earth as cold water or ice. The energy emitted from the precipitating water into the rarified air is then emitted back to outer space. I wonder if anyone has ever done the mathematical calculations to determine the absolute quantity of heat energy that is released from the oceans and sent on a one way ticket to the upper atmosphere where it is mostly sent back into space by the process of evaporation and precipitation cycles.

I read people saying there is unaccounted for heat hiding somewhere in the ocean, just waiting to strike the climate with a vengeance. But what if this energy isn't missing or hiding at all but slipping out the back door right before our very eyes by rising water vapor that is a conduit that pumps heat energy from the ocean back into space through continuous cycles of surface evaporation (picking up heat), rising 20,000 to 40,000 miles above the earth, and then releasing this energy into the freezing upper atmosphere when water precipitates and falls back to the earth. The heat cannot come back to earth because the precipitated water by definition gave up all its heat of vaporization and fusion to the upper atmosphere.

In short, rising water vapor is a one way conduit that removes heat from the ocean and all bodies of water and sends it up to the upper atmosphere, where it is released from the water, which falls back to earth depleted of heat, forming a heat gradient in the upper atmosphere. Because of entropy, hotter air always moves in the direction of colder air, which is air that is further from earth and closer to space. That means the heat that is released by precipitation is mostly lost to outer space. There is no mechanism to return it to earth.

Thus, the ocean is one giant heat pump that sends heat back to space through a process that is remarkably similar to how air conditioners work through a working fluid that evaporates to cool locally in one place and condenses to heat locally at another place. The cooling through evaporation is at the earth's surface, and the heating through condensation to release heat is at 20,000 to 40,000 feet where the heat is essentially given up by the earth for good.

I welcome all opinions and counterpoints.
Title: Re: Basic questions about melting physics
Post by: oren on August 30, 2019, 08:39:37 AM
Quote
I read people saying there is unaccounted for heat hiding somewhere in the ocean, just waiting to strike the climate with a vengeance. But what if this energy isn't missing or hiding at all but slipping out the back door right before our very eyes by rising water vapor that is a conduit that pumps heat energy from the ocean back into space 
I doubt you are describing it correctly, and I doubt "most energy is immediately lost to outer space", but regardless this mechanism has been in place forever, while ocean heat content growth is measurable and very real, so what is there to doubt?
Title: Re: Basic questions about melting physics
Post by: binntho on August 30, 2019, 08:56:19 AM
Quote
I read people saying there is unaccounted for heat hiding somewhere in the ocean, just waiting to strike the climate with a vengeance. But what if this energy isn't missing or hiding at all but slipping out the back door right before our very eyes by rising water vapor that is a conduit that pumps heat energy from the ocean back into space
I doubt you are describing it correctly, and I doubt "most energy is immediately lost to outer space", but regardless this mechanism has been in place forever, while ocean heat content growth is measurable and very real, so what is there to doubt?

I think in general FTB's essay has it right, but the particulars that oren points out are what needs closer scrutiny.

For one, the heat content of the oceans is something that can be (and is) measured directly, and it is rapidly increasing (causing most of the current sea level rise - the oceans are acting as their own old-fashioned thermometer).

As oren points out, the evaporative cycle is nothing new but it's there and it is probably conducting more heat the hotter the oceans get.

As for condensation, not all the water vapor condenses in the upper atmosphere - much of it condenses back to the surface (e.g. during nighttime) or close to the surface as fog. Not to forget the Foehn effect where heat released by condensation is brought down from the mountains into the lowlands, significantly raising near-surface temperatures.

And the heat released by cloud condensation is going to be radiative heat to a large degree, and given both greenhouse gases and the fact that this is happening inside a cloud, I don't think it's possible to claim that most of it gets lost to space. Much of it certainly, but how much? Does anybody know?

But in the end this is all just part of the heat balance, the flow of energy in the atmosphere (including the oceans), all very well measured and accounted for in total although the details may be a bit trickier.
Title: Re: Basic questions about melting physics
Post by: P-maker on August 30, 2019, 11:35:27 AM
Felltheburn,

To some extent, you are thinking along the right lines. Alternatively, you are messing up some of the basic physics.

As long as we are in the Tropics, everything is honkydory. Most physical processes take place well above 0C (or 273K). It is when you start using calories and F, your problems begin.

When in the Sub-tropics, some of the precipitation comes down as hail. In recent years, we have seen an increasing hail diameter and more devastating hailstorms spreading north. This may be a sign of the kind of physics you focus on. More evaporative cooling in combination with more humid air should eventually lead to bigger hail, if condensation nuclei are present.

Moving to Mid-latitudes, we begin to have the change-over from freezing rain to warm rain. Apparently, you have forgot to include the temperature of the falling rain. All heat evaporated is not simply sent out to outer space. Some of it will return to Earth as a mild, warm rain, where you would even enjoy getting your underpants wet from time to time.

Now, finally to the physical processes in the Arctic. Your idea that all evaporative cooling will eventually leave the Arctic cold and the World in thermal balance (had it not been for the wicked ocean heat storage), is simply wrong. The moisture advected from southerly latitudes (as well as the minor part of the moisture evaporated from open Arctic waters), will eventually have to come down again as either rain (above 0C), or as snow. In the latter case, we may see the opposite of "sublimation" - that is water vapour going directly into the frozen phase - which of course releases a lot more energy, than just converting water vapour directly into rain.

In the presence of cloud condensation nuclei, we will see hailstorms spreading north, and we will see rain and showers entering the Arctic during winter. What we have not seen yet, is the physical reaction from/to a clean - basically CCN-free - Arctic atmosphere. My guess would be that initially, we will see ice pellets, but eventually we will see drizzle as the Arctic temperatures during winter goes above 0C.

Sitting in Svalbard through the dark "drizzle season" is no great joy I would presume. Maybe it will be a great time to reflect on the basic physics of our time.

Cheers P





Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 30, 2019, 01:36:52 PM
Feeltheburn is not wrong in his understanding of the physics.  It may be a simplistic way of stating the processes.  In general, heat flows from a hot body to a colder body.  During evaporation, water vapor carries heat energy into the atmosphere, where it can dissipated to the surrounding air molecules.  This is many diverge in their analysis.  Feeltheburn stated that it is "mostly sent back to space."  P-maker states that, "some of it will return to earth."  The major question is how much?  Many modeler claim that a significant portion of the energy will simply return to the surface via the radiative effect due to the higher concentration of greenhouse gases.  This seems to be an overestimate as it involves heat flowing from a cooler to a warmer body.  Feeltheburn is probably close to the correct answer, and explains why so many have overestimated the warming effect of increasing atmospheric concentrations of greenhouse gases.  It would also help explain why the warmer waters entering the Arctic have not resulted in lower sea ice minima.
Title: Re: Basic questions about melting physics
Post by: binntho on August 30, 2019, 01:39:53 PM
Feeltheburn is probably close to the correct answer, and explains why so many have overestimated the warming effect of increasing atmospheric concentrations of greenhouse gases.  It would also help explain why the warmer waters entering the Arctic have not resulted in lower sea ice minima.

This got me confused. Who have been overestimting the warming effect of increased greenhous gases?

And am I missing something or haven't the lower sea ice minima been coming in at a regular rate as the oceans get warmer?

In the last few decades sea ice has declined drastically - so what is there to explain? Feeltheburn is, I feel, barking up the wrong tree altogether.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 30, 2019, 01:56:29 PM
Feeltheburn is probably close to the correct answer, and explains why so many have overestimated the warming effect of increasing atmospheric concentrations of greenhouse gases.  It would also help explain why the warmer waters entering the Arctic have not resulted in lower sea ice minima.

This got me confused. Who have been overestimting the warming effect of increased greenhous gases?

And am I missing something or haven't the lower sea ice minima been coming in at a regular rate as the oceans get warmer?

In the last few decades sea ice has declined drastically - so what is there to explain? Feeltheburn is, I feel, barking up the wrong tree altogether.

Based on the NSIDC data, sea ice minima were occurring roughly every three years until 2007.  Since then, there has been only one - in 2012.  Nine of the past eleven years have seen a higher minimum, and this year is likely to make ten.  The other year, 2016, barely edged out 2007 for a lower minimum.  All this has occurred while the oceans have been getting warmer.  So no, lower sea ice minima have NOT been coming at a regular rate as the oceans get warmer.
Title: Re: Basic questions about melting physics
Post by: binntho on August 30, 2019, 02:27:44 PM
Feeltheburn is probably close to the correct answer, and explains why so many have overestimated the warming effect of increasing atmospheric concentrations of greenhouse gases.  It would also help explain why the warmer waters entering the Arctic have not resulted in lower sea ice minima.

This got me confused. Who have been overestimting the warming effect of increased greenhous gases?

And am I missing something or haven't the lower sea ice minima been coming in at a regular rate as the oceans get warmer?

In the last few decades sea ice has declined drastically - so what is there to explain? Feeltheburn is, I feel, barking up the wrong tree altogether.

Based on the NSIDC data, sea ice minima were occurring roughly every three years until 2007.  Since then, there has been only one - in 2012.  Nine of the past eleven years have seen a higher minimum, and this year is likely to make ten.  The other year, 2016, barely edged out 2007 for a lower minimum.  All this has occurred while the oceans have been getting warmer.  So no, lower sea ice minima have NOT been coming at a regular rate as the oceans get warmer.

I think you are confusing random variability with trend. On a decadal trend, it is very obvious that sea ice has declined as ocean temps have gone up. Looking for that to happen every year is perhaps a bit simplistic.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 30, 2019, 02:34:22 PM
Feeltheburn is probably close to the correct answer, and explains why so many have overestimated the warming effect of increasing atmospheric concentrations of greenhouse gases.  It would also help explain why the warmer waters entering the Arctic have not resulted in lower sea ice minima.

This got me confused. Who have been overestimting the warming effect of increased greenhous gases?

And am I missing something or haven't the lower sea ice minima been coming in at a regular rate as the oceans get warmer?

In the last few decades sea ice has declined drastically - so what is there to explain? Feeltheburn is, I feel, barking up the wrong tree altogether.

Based on the NSIDC data, sea ice minima were occurring roughly every three years until 2007.  Since then, there has been only one - in 2012.  Nine of the past eleven years have seen a higher minimum, and this year is likely to make ten.  The other year, 2016, barely edged out 2007 for a lower minimum.  All this has occurred while the oceans have been getting warmer.  So no, lower sea ice minima have NOT been coming at a regular rate as the oceans get warmer.

I think you are confusing random variability with trend. On a decadal trend, it is very obvious that sea ice has declined as ocean temps have gone up. Looking for that to happen every year is perhaps a bit simplistic.

The decadal trend from the mid 90s to the mid 00s was definitively and largely downward.  The decadal trend since has been flat - a very slight increase starting at 2007, a similar decrease starting at 06 or 08.  I am not looking for it to happen every year - just more than once a decade.
Title: Re: Basic questions about melting physics
Post by: binntho on August 30, 2019, 02:54:39 PM
The decadal trend from the mid 90s to the mid 00s was definitively and largely downward.  The decadal trend since has been flat - a very slight increase starting at 2007, a similar decrease starting at 06 or 08.  I am not looking for it to happen every year - just more than once a decade.

I think you'll find that there is nowhere near enough datapoints to make statistically valid claims about changes in trends from one decade to another. In other words, it is not valid scientifically to say that there are differences in trend between one decade and another.

Besides just looking at a graph of minimums since the start of the satellite era shows a growing downwards trend, to match a growing warmin oceans trend.

But it's interesting that you think that Feeltheburn's hypothesis of having found a major missing piece in the whole field of meteorology can explain why your once-a-decade minimums aren't coming in (besides, I thought 2012 was this decade's minimum?)
Title: Re: Basic questions about melting physics
Post by: MyACIsDying on August 30, 2019, 04:57:01 PM
The AMOC has been weakening this decade to it's lowest strength, when the AMOC was a reason for arctic melt to increase, one would assume this weakening to minimum would mean increase in arctic ice extent? Clearly not.. so I wholly disagree on the flat lining trend of arctic ice melt. The 'Slow Transition' thread also explains reasons why extent is proportionally dropping less than volume is.

Klondike Kat I appreciate having your down to earth attitude on this forum but to say people are overestimating the effect GHG's?? I thought the science world was in general agreement that GHGs raising our radiation emittance roof is by far the largest reason for the change in thermodynamic equilibrium we know is happening by increases in heat content (.4Wms-2 imbalance to ~1200 Wms-2 incoming solar radiation may seem little but it accounts for all of the ~10^21 J /year OHC increase)

gerontocrat pointed out recently this is 130 times the energy used for our yearly losses to put that in perspective. Sure we can have localized feedback mechanisms that bring areas to cold extremes but I doubt any of these would be able overcome the global increase in temps in a permanent matter.

This is all assuming we keep the trend of GHG increase as it is.. I'm very curious what would happen if we lower the roof by taking CO2 out of the atmosphere? A cooldown faster than the warmup has taken I expect. Anyone know of models that ran such scenarios?
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 30, 2019, 05:45:55 PM
The AMOC has been weakening this decade to it's lowest strength, when the AMOC was a reason for arctic melt to increase, one would assume this weakening to minimum would mean increase in arctic ice extent? Clearly not.. so I wholly disagree on the flat lining trend of arctic ice melt. The 'Slow Transition' thread also explains reasons why extent is proportionally dropping less than volume is.

Klondike Kat I appreciate having your down to earth attitude on this forum but to say people are overestimating the effect GHG's?? I thought the science world was in general agreement that GHGs raising our radiation emittance roof is by far the largest reason for the change in thermodynamic equilibrium we know is happening by increases in heat content (.4Wms-2 imbalance to ~1200 Wms-2 incoming solar radiation may seem little but it accounts for all of the ~10^21 J /year OHC increase)

gerontocrat pointed out recently this is 130 times the energy used for our yearly losses to put that in perspective. Sure we can have localized feedback mechanisms that bring areas to cold extremes but I doubt any of these would be able overcome the global increase in temps in a permanent matter.

This is all assuming we keep the trend of GHG increase as it is.. I'm very curious what would happen if we lower the roof by taking CO2 out of the atmosphere? A cooldown faster than the warmup has taken I expect. Anyone know of models that ran such scenarios?

Thank you for your kind response.  The "people" to which I was referring are the posters here who claim that the current scientific thinking is too conservative and that the current warming is being masked by factor X, and once this is overcome, warming will skyrocket, causing all sorts of global catastrophes.  What if factor X for Arctic sea ice is just as FeeltheBurn has postulated, and will never be overcome?
Title: Re: Basic questions about melting physics
Post by: gerontocrat on August 30, 2019, 06:09:15 PM
I am not even going to try to get into the physics of the melting of ice. What I am looking at is what are the best measures of trends in sea ice loss (or gain)

When I was looking at trends in sea ice, like most people I used to look mostly at the sea ice annual minimum, and a little bit at the maximum. But as I started to make graphs of the Arctic in total, and then sea by sea, it became apparent that minimal reductions or even increases in the minimum could conceal significant reductions in sea ice.

I now have data that looks at ice-free days, open water percentages at various times of the year, and finally 365 trailing averages for extent, area and volume, the latter which  I attach. These show that although the 2012 JAXA extent minimum was 0.84 million km2 below any minimum since, the 2016 year produced a lower 365 day average. This was because sea ice was low for much longer than the crash in 2012.

2019 may now be looking like a bit of an end-of-season anti-climax, but nevertheless if refreeze is slow, the 365 day trailing average could well be a new record low by Spring 2020.

After the minimum, and after the end of the calendar year I hope to be able to show a similar story when looking at ice-free days and increases in open water.

So what am I saying - simply that minima may not be falling - but sea ice is declining.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 30, 2019, 06:35:14 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.
Title: Re: Basic questions about melting physics
Post by: gerontocrat on August 30, 2019, 06:58:54 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.
I just think that the minima to some extent disguise the loss of sea ice over time, and that the graphs I posted support that to some extent. I make no firm predictions about when a BOE etc etc will happen, but
- CO2 ppm will increase significantly for a good few years more on the most optimistic assumptions,
- the atmosphere will heat up for many more years,
- the Arctic will heat up faster than the average.

Ice and heat don't make long-lasting partners. The cryosphere in the Arctic will diminish, and so my very unfirm prediction is for summer sea ice to be very very much less by 2030, for which I cannot offer any evidence other than the above.
Title: Re: Basic questions about melting physics
Post by: sailor on August 30, 2019, 11:41:51 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.
I just think that the minima to some extent disguise the loss of sea ice over time, and that the graphs I posted support that to some extent. I make no firm predictions about when a BOE etc etc will happen, but
- CO2 ppm will increase significantly for a good few years more on the most optimistic assumptions,
- the atmosphere will heat up for many more years,
- the Arctic will heat up faster than the average.

Ice and heat don't make long-lasting partners. The cryosphere in the Arctic will diminish, and so my very unfirm prediction is for summer sea ice to be very very much less by 2030, for which I cannot offer any evidence other than the above.
Completely true. A good example is 2016 Winter. It’s kinda predictable what will come, but how, it will amuse us or terrify us
Title: Re: Basic questions about melting physics
Post by: binntho on August 31, 2019, 06:38:57 AM
When I was looking at trends in sea ice, like most people I used to look mostly at the sea ice annual minimum, and a little bit at the maximum. But as I started to make graphs of the Arctic in total, and then sea by sea, it became apparent that minimal reductions or even increases in the minimum could conceal significant reductions in sea ice.

I now have data that looks at ice-free days, open water percentages at various times of the year, and finally 365 trailing averages for extent, area and volume, the latter which  I attach. These show that although the 2012 JAXA extent minimum was 0.84 million km2 below any minimum since, the 2016 year produced a lower 365 day average. This was because sea ice was low for much longer than the crash in 2012.
...
So what am I saying - simply that minima may not be falling - but sea ice is declining.

I agree with you Gero, and I think that the three graphs you posted there are by far the best when it comes to looking at the real underlying trends.

But I am not so sure about the red polynomial lines on two of them - just from eyeballing I would have thought that a simple curve (i.e. second grade polynomial) with an increasing downwards curve would be the best match?
Title: Re: Basic questions about melting physics
Post by: binntho on August 31, 2019, 07:05:45 AM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.

I'm a bit surprised at your repeated claims here KK.

"The minimum was declining only slightly until the late 90s when it plummeted" is not correct, nor has it slowed "considerably" recently.

The attached is NSIDC daily minimum figures, up to and including 2019 at 4.3 4.6, which is appr. today's number. This graph does not allow any such statements, and there are no statistical models that will support anything other than a straight line.

The curve does jump up and down, but that cannot be shown to be other than random variability. So any and all guesses as to explanations for probably non-existent changes in trend are really a bit silly.

EDIT: The figure I used for 2019 was the Jaxa figure, NSIDC is apparently 0.3 MKm2 higher. Graph is corrected.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 31, 2019, 03:24:38 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.

I'm a bit surprised at your repeated claims here KK.

"The minimum was declining only slightly until the late 90s when it plummeted" is not correct, nor has it slowed "considerably" recently.

The attached is NSIDC daily minimum figures, up to and including 2019 at 4.3 4.6, which is appr. today's number. This graph does not allow any such statements, and there are no statistical models that will support anything other than a straight line.

The curve does jump up and down, but that cannot be shown to be other than random variability. So any and all guesses as to explanations for probably non-existent changes in trend are really a bit silly.

EDIT: The figure I used for 2019 was the Jaxa figure, NSIDC is apparently 0.3 MKm2 higher. Graph is corrected.

Your curve supports my claim as stated.  The minimum was decreasing slowly, until it took a bigger dive in the 90s.  That lasted about 15 years, depending on which curve fitting one chooses.  Since then, the minimum has flatlined.  Calling those significant chances random variability is quite the stretch.  Even the curve Gerontocrat presenter shows the changes.  My claim should come as no surprise to those who have been following the ice for the past years (decades),
Title: Re: Basic questions about melting physics
Post by: Archimid on August 31, 2019, 04:02:37 PM
So basically your argument is that "there has been no warming since 1998" adapted poorly to "Sea Ice stopped melting in 2012".

For that you use a pseudo explanation, seconded by the climate change deniers and validated by  Bintho's polite argument.

Quote
The "people" to which I was referring are the posters here who claim that the current scientific thinking is too conservative and that the current warming is being masked by factor X, and once this is overcome, warming will skyrocket, causing all sorts of global catastrophes. 

This has already happened and will keep happening and getting worse. You can't see it because fear blinds you, but you will feel it soon regardless if you understand what is happening or not.
Title: Re: Basic questions about melting physics
Post by: gerontocrat on August 31, 2019, 04:51:47 PM
I agree with you Gero, and I think that the three graphs you posted there are by far the best when it comes to looking at the real underlying trends.

But I am not so sure about the red polynomial lines on two of them - just from eyeballing I would have thought that a simple curve (i.e. second grade polynomial) with an increasing downwards curve would be the best match?
So did I, so I told it to do it, and it produced a lunatic U curve pointing UP, and a lousy R2. So I looked for a reasonable R2 and a result not showing ridiculous future increases or decreases. The ones on the graphs are the best I could do. But I don't like these red trend lines either. These periodic large rises and falls are just as well represented by an obviously untrue linear projection.

My own pure guess is that we are looking at 2 steps down, 1 step up as the years go by until the ice gets so thin and fragmented that in a year favourable for melting - poof ! (as posters have shown here and there on the melting season thread). But that is pure speculation (that now belongs to me since I stole it from others).
Title: Re: Basic questions about melting physics
Post by: binntho on August 31, 2019, 05:14:28 PM
Calling those significant chances random variability is quite the stretch. 
<snip> 
My claim should come as no surprise to those who have been following the ice for the past years (decades),

Well yes, I've seen the same claim made over and over again over the last few years and every time I try to point out that it simply can't be done that way. The points are way too few, the variation far too big, to be able to claim with any statistical support whatsoever that the trend has changed during the satellite era.

This is not to say that there has not been a change in trend, but statistical analysis will not support this. It is not good enough to squint at the chart and say, "it seems to me that the trend is bigger here than there ..." It can be good fun, and it can be very interesting to try to figure out why the trend has changed (that is, of course, if it has changed and it's not just natural variability).

But going from "it looks to me like the trend has been changing" to taking Feeltheburns attempts at rewriting meteorology to support this feeling is a huge stretch, literally an immaginative jump. And as such, pretty silly.

And look at the graph again, and compare it to this famous graph, copied from tamino's webpage. It's obvious, isn't it, that there is a change in trend between the 90s, the noughts and the teens? The noughts are obviously stalling.

(https://tamino.files.wordpress.com/2019/01/nasa1y.jpg)

But no, Tamino has shown again and again that statistically there was no pause in global warming in the noughts - it just looks that way because of the randomness of natural variability.

And the same goes for the changes in SIE minimums over the last four decades - randomnes and natural variability are just as good an explanation as any hypothetical state changes leading to changes in melting rate.

https://tamino.wordpress.com/
Title: Re: Basic questions about melting physics
Post by: binntho on August 31, 2019, 05:18:32 PM
I agree with you Gero, and I think that the three graphs you posted there are by far the best when it comes to looking at the real underlying trends.

But I am not so sure about the red polynomial lines on two of them - just from eyeballing I would have thought that a simple curve (i.e. second grade polynomial) with an increasing downwards curve would be the best match?
So did I, so I told it to do it, and it produced a lunatic U curve pointing UP, and a lousy R2.
I tried the same and got the same result. Doh!
Title: Re: Basic questions about melting physics
Post by: binntho on August 31, 2019, 05:25:20 PM
For that you use a pseudo explanation, seconded by the climate change deniers and validated by  Bintho's polite argument.

*sigh* I keep forgetting that there are Americans reading this blog. What I did was what we in Europe call "a polite rejection", similar to the Chinese custom of helping your opponent maintain face.

As Mrs. Brown would say, "that's nice".

Besides, Feeltheburn's small essay was well written and started off fine, but it ended in a very strange conclusion, so dealing politely with it seemed to me to be the best thing. But did I validate his conclusion? I hope not.
Title: Re: Basic questions about melting physics
Post by: Archimid on August 31, 2019, 05:37:04 PM
Your second reply completely invalidates his conclusion with a very appropriate language and tone. Thank you for that great reply and thank you for proving me wrong.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 31, 2019, 05:44:15 PM
Calling those significant chances random variability is quite the stretch. 
<snip> 
My claim should come as no surprise to those who have been following the ice for the past years (decades),

Well yes, I've seen the same claim made over and over again over the last few years and every time I try to point out that it simply can't be done that way. The points are way too few, the variation far too big, to be able to claim with any statistical support whatsoever that the trend has changed during the satellite era.

This is not to say that there has not been a change in trend, but statistical analysis will not support this. It is not good enough to squint at the chart and say, "it seems to me that the trend is bigger here than there ..." It can be good fun, and it can be very interesting to try to figure out why the trend has changed (that is, of course, if it has changed and it's not just natural variability).

But going from "it looks to me like the trend has been changing" to taking Feeltheburns attempts at rewriting meteorology to support this feeling is a huge stretch, literally an immaginative jump. And as such, pretty silly.

And look at the graph again, and compare it to this famous graph, copied from tamino's webpage. It's obvious, isn't it, that there is a change in trend between the 90s, the noughts and the teens? The noughts are obviously stalling.

(https://tamino.files.wordpress.com/2019/01/nasa1y.jpg)

But no, Tamino has shown again and again that statistically there was no pause in global warming in the noughts - it just looks that way because of the randomness of natural variability.

And the same goes for the changes in SIE minimums over the last four decades - randomnes and natural variability are just as good an explanation as any hypothetical state changes leading to changes in melting rate.

https://tamino.wordpress.com/

That graph us an excellent example.  Would you use a simple linear curve for that data?  Of course not, it is polymeric in nature.  The R2 would tell you that.  Just like Gerontocrat has been trying to tell you with his graphs.  Using a simple linear regression does not tell the whole story.  Does the line in his graphs tell the whole story?  Probably not.  However, it is a better analysis than a straight line.  Selective curve fitting to match ones own beliefs, is one of the reasons that several people have erroneously predicted that the Arctic would be ice-free by now.  The Arctic sea ice minimum has not decreased recently.  If you refuse to see that from the data, there is nothing more that I can say.
Title: Re: Basic questions about melting physics
Post by: oren on August 31, 2019, 05:50:15 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.
At what point did FTB's description include anything about a change in the described mechanism? Evaporation from the ocean is nothing new.  Why would it suddenly halt sea ice loss? Regardless of whether there has been or hasn't been a hiatus in ice loss, his description doesn't explain anything at all.
KK, do you believe global ocean heat content has been rising, or is it stable maybe? If it is rising, FTB's description is irrelevant.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 31, 2019, 06:15:42 PM
Geronocrat,
I agree that the ice has been generally in decline for the past four decades.  This occurred slowly at first, as the maximum sea ice started to fall.  The minimum was declining only slightly until the late 90s, when it plummeted.  This led to ab overall ice declined at a much faster rate until recently, when it has slowed considerably.  This occurred during the time that many pundits predicted an accelerated loss in Arctic sea ice to near ice-free conditions this decade.    All I am saying is that that his explanation is plausible explanation for the change.
At what point did FTB's description include anything about a change in the described mechanism? Evaporation from the ocean is nothing new.  Why would it suddenly halt sea ice loss? Regardless of whether there has been or hasn't been a hiatus in ice loss, his description doesn't explain anything at all.
KK, do you believe global ocean heat content has been rising, or is it stable maybe? If it is rising, FTB's description is irrelevant.

Globally, yes.  That may not be true in the Arctic.  The lessening of Arctic sea will cause more evaporative losses.  Heat is lost more readily at the poles than elsewhere.
Title: Re: Basic questions about melting physics
Post by: oren on August 31, 2019, 07:01:44 PM
I wonder then how it is that seas which lose their sea ice cover earlier (such as the Chukchi) have warmer SSTs than in the past. You would think that this newfound evaporation scheme would cool them somehow.
Note: I don't have access to a ready-made chart for this claim, but am pretty sure it is true based on following the melting seasons.
Title: Re: Basic questions about melting physics
Post by: Glen Koehler on August 31, 2019, 08:06:09 PM
  The Arctic sea ice minimum has not decreased recently.  If you refuse to see that from the data, there is nothing more that I can say.

KK - depends on what you mean by "recently."  Given the internal variability of the system, a 7-year or 10-year window (i.e. since 2012, 2008) is too short to draw conclusions.  To protect against cherry picking and our innate human tendency for "pattern matching" where there is none, a longer interval of at least 20 years is required. 

     The 20-year downward trend in annual minimum Arctic sea ice volume appears to be much larger than year-to-year variation, and thus appears to be statistically significant.  Maybe somebody with more time and skill will run the stats on 1998-2018 annual min. volume data.  Moreover, 2019 is likely to end up with less the 4M km3, and thus land right on and thus reinforce the PIOMAS trend shown at
http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAprSepCurrent.png (http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAprSepCurrent.png)

    I think focusing so much on Extent leads us to false conclusions on both the high and low side.  2012 was bad for volume, but not nearly as extreme as it was for Extent.  To a substantial degree, Extent reflects temporary wind and current conditions, not the true status of the Arctic sea ice.  By focusing on Extent we can under-represent the cumulative progressive effects on overall condition of the ice. 

     The ice year this year has looked weaker more fractured than in past years.  A subjective measure to be sure, but not to be fully discounted either.  It will be interesting to see how the MYI numbers look after the 2019 melt season.  My guess is that they took another downward hit such that we are getting very close to only 1st and 2nd year ice that is more vulnerable than the tough old 5- and even 10-year old ice of the recent past.  The final phase of decline in ASI Extent is slowed by the much more rapid regrowth of 1st year ice.  But the flip side of that is that 1st year ice also melts out faster.   In retrospect, the functional loss of the Beaufort Sea ice nursery may be seen as a crucial event marking the beginning of the end of ASI in Aug-Sept.   I suspect with only 1st-year ice to get rid of at the start of future melt seasons, it won't last much beyond July 31.

     That's how it looks to me anyway.  No formal training in Arctic or ice, just a little experience analyzing numbers and interpreting science added to lurking in the ASIF.  Thanks to those who provide interesting info and speculation to ASIF.  Esp. thanks to Neven, Gero, JCG, uniquorn, Alphabet and others. Less gratitude for those who engage in extended ego-defensive debates.  To those folks I say, let others disagree with you and get over it.  Nobody else cares if somebody insults you.  Now you can disagree with me! 
Title: Re: Basic questions about melting physics
Post by: gerontocrat on August 31, 2019, 08:12:58 PM
I wonder then how it is that seas which lose their sea ice cover earlier (such as the Chukchi) have warmer SSTs than in the past. You would think that this newfound evaporation scheme would cool them somehow.
Note: I don't have access to a ready-made chart for this claim, but am pretty sure it is true based on following the melting seasons.
Google provides...
https://arctic.noaa.gov/Report-Card/Report-Card-2015/ArtMID/5037/ArticleID/220/Sea-Surface-Temperature

A bit out of date (only to 2015) but I am sure given recent data that the only way was up.

Quote
The Chukchi Sea and eastern Baffin Bay show the largest ocean surface warming trends; August SSTs are increasing at ~0.5°C/decade in these regions.
Title: Re: Basic questions about melting physics
Post by: gerontocrat on August 31, 2019, 08:57:32 PM
Oren - you sent me on the hunt for data....

A bit more... from NOAA Report Card 2018
https://www.arctic.noaa.gov/Report-Card/Report-Card-2018/ArtMID/7878/ArticleID/779/Sea-Surface-Temperature

Quote
Mean August SSTs from 1982-2018 show warming trends over much of the Arctic Ocean; statistically significant (at the 95% confidence interval) linear warming trends of up to +1° C decade-1 are observed (Figs. 1d and 2). These warming trends coincide with declining trends in summer sea-ice extent (including late-season freeze-up and early melt, e.g., Parkinson, 2014), increased solar absorption (e.g., Timmermans et al., 2018), and increased vertical ocean heat transport (e.g., Lind et al., 2018).
Title: Re: Basic questions about melting physics
Post by: oren on August 31, 2019, 10:38:03 PM
Thank you G.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on August 31, 2019, 10:49:32 PM
  The Arctic sea ice minimum has not decreased recently.  If you refuse to see that from the data, there is nothing more that I can say.

KK - depends on what you mean by "recently."  Given the internal variability of the system, a 7-year or 10-year window (i.e. since 2012, 2008) is too short to draw conclusions.  To protect against cherry picking and our innate human tendency for "pattern matching" where there is none, a longer interval of at least 20 years is required.

Glen, I fear you may be the one engaging in cherry picking.  By choosing a start date of 1998, you are ensuring the largest possible decreasing trend.  Contrarily, I choose the entire 40/year dataset.   The 7- or 10-year window only appears too short to you, because it does give the trend you want to see.  That is one of the main reasons I prefer analyses by well-established scientists over others.
Title: Re: Basic questions about melting physics
Post by: nanning on September 01, 2019, 04:08:48 AM
<snip>
Nobody else cares if somebody insults you.

Good post imo Glen but I disagree with this last bit because I do care.
If somebody uses nasty language, impolite insults, name calling etc. they don't get a like from me, even if I think the rest of the post is really good.
I don't think it has any influence but it is my way. In some cases I'll post a question about it.

OK back to topic, sorry.
Title: Re: Basic questions about melting physics
Post by: binntho on September 01, 2019, 08:42:16 AM
That graph us an excellent example.  Would you use a simple linear curve for that data?  Of course not, it is polymeric in nature.  The R2 would tell you that.
I doubt very much if it is "polymeric" in "nature" - whatever that means. Can a graph have a "nature"? And if you are so sure of the R2, why not try yourself?

Me, I am nowhere near good enough at statistics to make such claims, but I have been following Tamino's blog for some years, and he is a true master of the art.

His latest post is actually about this very thing, i.e. how has the rate of warming changed over the last 150 years or so. And funnily enough, he doesn't even mention the "polymeric nature" of the graph.

Here, on the other hand, is that graph with some statistically valid change points and linear trends connecting them. This is apparently statistically the best fit to the data. (https://tamino.wordpress.com/2019/08/20/global-warming-how-fast/)

(https://tamino.files.wordpress.com/2019/08/model2.jpg)

Quote

 Just like Gerontocrat has been trying to tell you with his graphs.  Using a simple linear regression does not tell the whole story.  Does the line in his graphs tell the whole story?  Probably not.  However, it is a better analysis than a straight line.


If Gerontocrat tried to tell me something, I'm sure that he would succeed. And I do not recall him trying to tell me that graphs have "polymeric" natures, or that his polymeric line is a "better analysis" than a straight line. So what does Gero himself have to say about his polymeric red lines?

But I don't like these red trend lines either. These periodic large rises and falls are just as well represented by an obviously untrue linear projection.

Which is perfectly reasonable. A linear trend is simply the only thing that matches the data we have in any statistically valid sense. And before somebody points this out, I am well aware that the R2 values for the polynomials are slightly better than for the linears, but that is still not valid since these graphs are running averages.

If you run linear and polynomial regressions on the raw data you get identical R2 values of c.a. 0.037 (because of the very large variance, the R2 is quite low), no visible trend changes in the polynomial within the period in question, and a downward trend of 73.000 km2 per annum for both.

Funnily enough, this graph plotting the NSIDC values shows a downward trend of 81.100 km2 per annum, while Gero's SIE 365 day running average linear regression shows a downward trend of 67.291 km2 per annum.

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=2709.0;attach=131600;image)
Missing from the graph is the formula y = -0.0811x + 168.03 and an R2 of 0.7803.


The problem arises when people try to extend the linear trend into a linear projection and get different answers from different graphs. So clearly, the linear trends cannot be used to project the zero point. That does not mean that other strangely looking swirly polynomials are going to do any better. To repeat: There are not enough data points in the minimum graph, and the variance is too big to justify anything other than a linear trend.

Quote
Selective curve fitting to match ones own beliefs, is one of the reasons that several people have erroneously predicted that the Arctic would be ice-free by now.  The Arctic sea ice minimum has not decreased recently.  If you refuse to see that from the data, there is nothing more that I can say.

We can agree that selective curve fitting is a no-go. But I can only agree with your statement that the minimum has not "decreased recently" if we always define "recently" as "since the last record minimum".

The problem with your statements, KK, is that you think you can see trend changes in the graph. I claim that the graph has too few data points and too much variance to justify such claims.  So the "not decreased recently" is a real thing for now, but has no actual meaning - it is not possible, based on the data, to make claims about a statistically valid change in trend.

(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=2709.0;attach=131600;image)

That is not to say that there isn't a change in the underlying forces that interact in the high Arctic and give us minimums every year. Perhaps something has changed that makes new record minimums very unlikely, or perhaps that was always built into the system, that the graph would eventually flatline around this level.

And yes, just looking at the graph of SIE minimums can well make you think that this is what is happening. But there is no statistically valid basis to such claims, and probably won't be for another 10 years or so. If, in 2029, we are still hovering around the 4M mark, a change in trend will be statistically valid. Today it is not.

And when you seek weird explanations (such as Feeltheburn's erraneous understanding of meteorology) to explain your non-statistically-valid claims, then we are way into the land of silliness.
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 01, 2019, 10:52:17 AM
Kat, what you see as a stalling is most likely variance. Variance is expected in a highly complex/chaotic system. Given the context, it's extremely unlikely that it is indeed a stalling.

Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 03:10:51 PM
Kat, what you see as a stalling is most likely variance. Variance is expected in a highly complex/chaotic system. Given the context, it's extremely unlikely that it is indeed a stalling.

If it were truly variance, it should be random.  Look at the graph and trend posted by binntho.  From 96 to 06, all the variance was above the trend.  Then, there were six straight years below the trend, some substantially.  There is no physical reason that the ice should follow a linear line.  Perhaps it is just variance, but it has shown variance in a flattening direction for over a decade now.  How long must it occur, before it becomes acceptable?
Title: Re: Basic questions about melting physics
Post by: binntho on September 02, 2019, 03:52:28 PM
Kat, what you see as a stalling is most likely variance. Variance is expected in a highly complex/chaotic system. Given the context, it's extremely unlikely that it is indeed a stalling.

If it were truly variance, it should be random.  Look at the graph and trend posted by binntho.  From 96 to 06, all the variance was above the trend.  Then, there were six straight years below the trend, some substantially. 


Even if it is possible for the human mind to see patterns doesn't mean that they aren't the product of random variance. Co-incidence and randomness could indeed well produce the pattern we all see in the graphs.

This whole discussion really revolves around the number of datapoints. With only 40 datapoints it's not possible to claim anythying statistically other than that a linear trend is a fairly good fit.

Quote

There is no physical reason that the ice should follow a linear line.  Perhaps it is just variance, but it has shown variance in a flattening direction for over a decade now.  How long must it occur, before it becomes acceptable?

There is a very good physical reason for the ice to follow what seems to be a linear trend over the 40 year period - global temperatures have been rising with a linear trend during the same time, and lower SIE is a direct consequence of higher temperatures.

As can be seen in my earlier graph, the closest we can say statistically about the temperature change over the 40 year period is that it has risen linearly. Therefore we should a priori expect sea ice extent to fall linearly.

On the other hand, we can all come up with lots of reasons for why the rate of diminishing SIE or rate of falling minimums etc. should not be linear, at least not always and under all circumstances. The drastic loss of MYI is certainly one of the most obvious ones, the shape of the Arctic ocean another.

But there are lots of other factors at play, such as the relentlessly rising ocean temperatures, the increasing storminess, and the essential randomness of weather coupled with the apparent sensitivity of the melting season to the "right" type of weather at the "right" time.

So at least from my point of view, declaring the linear trend to be dead and void is much too premature. I'll repeat what I said earlier - let's wait another 10 years, and then we'll (perhaps) be able to tell if there really was a change in trend 10 years ago.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 04:44:34 PM
Kat, what you see as a stalling is most likely variance. Variance is expected in a highly complex/chaotic system. Given the context, it's extremely unlikely that it is indeed a stalling.

If it were truly variance, it should be random.  Look at the graph and trend posted by binntho.  From 96 to 06, all the variance was above the trend.  Then, there were six straight years below the trend, some substantially. 


Even if it is possible for the human mind to see patterns doesn't mean that they aren't the product of random variance. Co-incidence and randomness could indeed well produce the pattern we all see in the graphs.

This whole discussion really revolves around the number of datapoints. With only 40 datapoints it's not possible to claim anythying statistically other than that a linear trend is a fairly good fit.

Quote

There is no physical reason that the ice should follow a linear line.  Perhaps it is just variance, but it has shown variance in a flattening direction for over a decade now.  How long must it occur, before it becomes acceptable?

There is a very good physical reason for the ice to follow what seems to be a linear trend over the 40 year period - global temperatures have been rising with a linear trend during the same time, and lower SIE is a direct consequence of higher temperatures.

As can be seen in my earlier graph, the closest we can say statistically about the temperature change over the 40 year period is that it has risen linearly. Therefore we should a priori expect sea ice extent to fall linearly.

On the other hand, we can all come up with lots of reasons for why the rate of diminishing SIE or rate of falling minimums etc. should not be linear, at least not always and under all circumstances. The drastic loss of MYI is certainly one of the most obvious ones, the shape of the Arctic ocean another.

But there are lots of other factors at play, such as the relentlessly rising ocean temperatures, the increasing storminess, and the essential randomness of weather coupled with the apparent sensitivity of the melting season to the "right" type of weather at the "right" time.

So at least from my point of view, declaring the linear trend to be dead and void is much too premature. I'll repeat what I said earlier - let's wait another 10 years, and then we'll (perhaps) be able to tell if there really was a change in trend 10 years ago.

I will agree with much of what you says.  40 data points is not possible to claim anything statistically.  Although, we can say with much confidence that today is lower that 40 years ago.  Focusing on just the data from the annual minimum is not the best method of analyzing the sea ice, but it tends to get the most attention.   Yes, many factors are in play, such that correlating sea ice directly to global temperatures may not be the best practice.  I have no reason to believe that the sea ice will show a flat trend for another 10 years, but if it does, than I would expect most to accept the change in trend.  The sharp decline in sea ice has only shown a ~15-year trend, so they would be on par. 

One final point.  Sea ice analyses, no matter which metric, treats the entire ice as one.  In reality, it is made up of several small seas, bays, etc., and one large central ocean.  Much of the previous changes occurred largely in the peripheral seas, and less so in the central Arctic basin.  We may just be seeing a shift to the new regime.
Title: Re: Basic questions about melting physics
Post by: binntho on September 02, 2019, 05:01:23 PM
I will agree with much of what you says.  40 data points is not possible to claim anything statistically.  Although, we can say with much confidence that today is lower that 40 years ago. 

To be specific: 40 datapoints are not enough to decide whether there has been a change in trend. But it's plenty sufficient to show that there is a downward trend!

Quote

Focusing on just the data from the annual minimum is not the best method of analyzing the sea ice, but it tends to get the most attention.   


Absolutely, and the graphs that Gerontocrat has made from the 365 day averages are vastly to be preferred.

Quote
Yes, many factors are in play, such that correlating sea ice directly to global temperatures may not be the best practice.  I have no reason to believe that the sea ice will show a flat trend for another 10 years, but if it does, than I would expect most to accept the change in trend.  The sharp decline in sea ice has only shown a ~15-year trend, so they would be on par. 


If the trend flatlines for the next 10 years then I think that it's going to be pretty obvious, and statistically valid as well. And if there is an underlying dynamic that has cause a stall the last 10 years, why shouldn't it continue?

On the other hand, if the trend does not flatline then a hypothetical change in trend becomes unproven - but the underlying dynamics may still have been at work, flatlining for a period, but too hidden by the noisiness of the signal to be statistically detectable.

And your last comment, that the sharp decline in sea ice has shown a ~15 year trend, is again not something that cannot be stated with any statistical validity. There is no 10 or 15 or 20 year trends that can be read out of the minimum graphs, or the 365 day average graphs.

The only trend that can be read out of the graphs is that sea ice has been declining, and as far as the statistics go, basically linearly for the last 40 years.

Quote
One final point.  Sea ice analyses, no matter which metric, treats the entire ice as one.  In reality, it is made up of several small seas, bays, etc., and one large central ocean.  Much of the previous changes occurred largely in the peripheral seas, and less so in the central Arctic basin.  We may just be seeing a shift to the new regime.

Yes that's absolutely true, as I indicated earlier by mentioning the shape of the Arctic ocean. And a hypothetical "shift to a new regime" could well be an explanation for a hypothetical "stall". And if there is indeed such a shift then I would expect the stall to easily last the next 10 years.
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 02, 2019, 05:20:40 PM
If it were truly variance, it should be random.

OK, you don't understand what randomness is. That's a common problem with humans.

Quote
If you roll a fair, 6-sided die, there is an equal probability that the die will land on any given side.

Meaning, if you roll a dice, you have always the chance to roll a 6. So, if you roll 20 times a 6 in a row, it is ... well ... completely random! :)
Title: Re: Basic questions about melting physics
Post by: crandles on September 02, 2019, 05:36:11 PM
To be specific: 40 datapoints are not enough to decide whether there has been a change in trend. But it's plenty sufficient to show that there is a downward trend!

The number of datapoints needed does of course depend on how much the trend changes, the level of noise in the data, and perhaps other factors.

Also 40 datapoints is not all we have got. We have other months data which also show similar shapes. How much use that is may depend on autocorrelation, but I think there isn't much autocorrelation between maximum and minimum.

So anyone want to venture a calculation of when we should be able to say change of trend is statistically significant rather than just plucking 10 years out of the air? 10 years seems a bit long to me if the difference in trend rate is noticeably different. If new data points tend to be just above long term linear rate then it will take a long time, probably longer than 10 years. So the answer may need to be in terms of 'if x difference then y years but if z different then w years. So maybe a better question is at what statistical level of confidence are we at now? (Where not reasonably established until 95% confidence reached.)
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 05:40:14 PM
If it were truly variance, it should be random.

OK, you don't understand what randomness is. That's a common problem with humans.

Quote
If you roll a fair, 6-sided die, there is an equal probability that the die will land on any given side.

Meaning, if you roll a dice, you have always the chance to roll a 6. So, if you roll 20 times a 6 in a row, it is ... well ... completely random! :)

Really?  I would question your die.  That odds of that occurring is less than 1 in a trillion.  You call that random, and have the audacity to question my understanding of randomness?!
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 02, 2019, 06:01:03 PM
That odds of that occurring is less than 1 in a trillion.

And? What has odds to do with how the dice will fall?

The dice can't remember it's recent states and it has no understanding of the concept of 'odds'. It just obeys physics.

I'm having a bitcoin mining background which is the ultimate lesson in understanding randomness. I got this, Kat, believe me.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 06:07:22 PM
That odds of that occurring is less than 1 in a trillion.

And? What has odds to do with how the dice will fall?

The dice can't remember it's recent states and it has no understanding of the concept of 'odds'. It just obeys physics.

I'm having a bitcoin mining background which is the ultimate lesson in understanding randomness. I got this, Kat, believe me.

What does the odds have to do with how the dice fall?  Everything!  While each individual throw has the same odds, over time, they will even out, each number occurring nearly equally.  Straight-forward mathematics.  Should one number dominate against all odds, I would seriously question the integrity of the die.  This has nothing to do with physics, unless the die is loaded, causing the number 6 to occur repeatedly.
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 02, 2019, 06:15:44 PM
each individual throw has the same odds

Stop right there. This is really all there is to it.

It's not math. Math is a tool to calculate the odds. The math doesn't make the odds.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 06:55:00 PM
each individual throw has the same odds

Stop right there. This is really all there is to it.

It's not math. Math is a tool to calculate the odds. The math doesn't make the odds.

If you truly understand the odds, then why are you having such a hard time grasping the improbability of 20 straight sixes?
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 02, 2019, 07:16:28 PM
If you truly understand the odds, then why are you having such a hard time grasping the improbability of 20 straight sixes?

I'm not talking about the odds, Kat. You do. I'm talking about randomness.

You can't know the odds concerning the arctic area/extent numbers. And here we go full circle. :)

You can though, given the context, make assumptions about the odds. And they tell me this is most likely variance.
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 02, 2019, 07:21:27 PM
If you truly understand the odds, then why are you having such a hard time grasping the improbability of 20 straight sixes?

I'm not talking about the odds, Kat. You do. I'm talking about randomness.

You can't know the odds concerning the arctic area/extent numbers. And here we go full circle. :)

You can though, given the context, make assumptions about the odds. And they tell me this is most likely variance.

So, depending on ones assumptions, determined ones assessment.  Hence, they is little agreement.
Title: Re: Basic questions about melting physics
Post by: blumenkraft on September 02, 2019, 07:27:09 PM
Hence, they is little agreement.

Totally agree to disagree. :)
Title: Re: Basic questions about melting physics
Post by: petm on September 02, 2019, 07:35:11 PM
Are you talking about rolling 1 six after having rolled five sixes already, or rolling 6 sixes after having rolled none? Completely different questions.

Also, wtf?  ??? ;D
Title: Re: Basic questions about melting physics
Post by: crandles on September 02, 2019, 07:39:28 PM
(https://tamino.files.wordpress.com/2016/07/ice_change.jpg)

Quote
To know whether or not those indicated changes are real or just the impression given by random noise, a good way is to apply changepoint analysis. That confirms that these changes are indeed real, and gives the following “continuous piecewise linear” model of the anomalies.

https://tamino.wordpress.com/2016/07/17/arctic-heat/

Seems like Tamino confirmed it was real/statistically significant back in 2016?

We are rather off topic lets move this to https://forum.arctic-sea-ice.net/index.php/topic,2348
(When will the Arctic Go Ice Free?)
Title: Re: Basic questions about melting physics
Post by: petm on September 03, 2019, 12:55:29 AM
There is a brief discussion of latent heat fluxes (which are clearly well understood by climate scientists) mentioned up-thread in part 2 of this video (@~7 min). The whole video is well worth watching, as are all of the channel's videos. Solid, current climate science explained well in laymen's terms.

https://www.youtube.com/watch?v=uBngaoG_-6A

PS. Should I move this to a different thread, and where?
Title: Re: Basic questions about melting physics
Post by: Klondike Kat on September 03, 2019, 03:56:31 AM
Thanks crandles.  Will do.
Title: Re: Basic questions about melting physics
Post by: nanning on September 03, 2019, 07:43:44 AM
binntho, you have me mixed up with crandles. It was his/her find and posts:
https://forum.arctic-sea-ice.net/index.php/topic,2709.msg226369.html#msg226369
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg226396.html#msg226396
Title: Re: Basic questions about melting physics
Post by: binntho on September 03, 2019, 07:58:49 AM
binntho, you have me mixed up with crandles. It was his/her find and posts:
https://forum.arctic-sea-ice.net/index.php/topic,2709.msg226369.html#msg226369
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg226396.html#msg226396

You are quite right nanning - my mistake, I've corrected it in the post above. Thanks!

EDIT: I've moved the post to the "When will the Arctic go Ice Free" thread as suggested by Crandles. Seems like I'm just now waking up, after 2 hours of hectic activity!

https://forum.arctic-sea-ice.net/index.php/topic,2348.msg226465.html#msg226465
Title: Re: Basic questions about melting physics
Post by: Feeltheburn on September 23, 2019, 09:33:23 AM
Felltheburn,

To some extent, you are thinking along the right lines. Alternatively, you are messing up some of the basic physics.

As long as we are in the Tropics, everything is honkydory. Most physical processes take place well above 0C (or 273K). It is when you start using calories and F, your problems begin.

When in the Sub-tropics, some of the precipitation comes down as hail. In recent years, we have seen an increasing hail diameter and more devastating hailstorms spreading north. This may be a sign of the kind of physics you focus on. More evaporative cooling in combination with more humid air should eventually lead to bigger hail, if condensation nuclei are present.

Moving to Mid-latitudes, we begin to have the change-over from freezing rain to warm rain. Apparently, you have forgot to include the temperature of the falling rain. All heat evaporated is not simply sent out to outer space. Some of it will return to Earth as a mild, warm rain, where you would even enjoy getting your underpants wet from time to time.

Now, finally to the physical processes in the Arctic. Your idea that all evaporative cooling will eventually leave the Arctic cold and the World in thermal balance (had it not been for the wicked ocean heat storage), is simply wrong. The moisture advected from southerly latitudes (as well as the minor part of the moisture evaporated from open Arctic waters), will eventually have to come down again as either rain (above 0C), or as snow. In the latter case, we may see the opposite of "sublimation" - that is water vapour going directly into the frozen phase - which of course releases a lot more energy, than just converting water vapour directly into rain.

In the presence of cloud condensation nuclei, we will see hailstorms spreading north, and we will see rain and showers entering the Arctic during winter. What we have not seen yet, is the physical reaction from/to a clean - basically CCN-free - Arctic atmosphere. My guess would be that initially, we will see ice pellets, but eventually we will see drizzle as the Arctic temperatures during winter goes above 0C.

Sitting in Svalbard through the dark "drizzle season" is no great joy I would presume. Maybe it will be a great time to reflect on the basic physics of our time.

Cheers P

Thank you for your thoughtful response. Just trying to understand processes that no doubt affect weather, which is dynamic, but which may not be well accounted for in the climate models.
Title: Re: Basic questions about melting physics
Post by: Glen Koehler on April 21, 2020, 12:18:34 AM
     The Lebedev formula translates cumulative FDD into ice thickness, and yes, through the 0.58 exponential term represents the declining increase in ice thickness as FDD accumulate.  As shown in the Chris Reyolds posts, that formula can be used to estimate the difference in ice thickness additions between two cumulative FDD values.
   
     But what about the reverse process?  Is there a melting DD equivalent?  It seems likely that someone has measured that relationship.  A direct physical approach would be to measure ice thinning effects on blocks of sea ice of different thicknesses kept in a controlled setting and exposed to different temperature regimes. 

     A large scale field-based empirical approach might be possible by correlating Arctic seasonal temperature observations with subsequent reductions in Extent, Thickness, and Volume.  In addition to air and/or sea temperature, I suspect that such a study would need to also account for other factors such as cloud cover/solar radiation and wind, and also for the timing of those melting factor inputs on melt pond formation and surface changes to albedo. 

     This question seems so fundamental to understanding Arctic sea ice behavior that it must have been tackled by multiple research projects.  Most of my exposure to Arctic research is from what shows up in climate blogs, lay press articles, and on ASIF.  Minimal effort literature searching has not found anything to address this question, and that's all the time I have available at present. 

     What I am looking for is research relevant to melting DD vs. ice loss, and in particular to the effect of sea ice thickness on subsequent rate of thickness decline in response to melting DD.  The assumption that thinner ice melts faster than thick ice is often stated, and it makes sense due to salinity, structural weakness, surface/volume ratio, etc.  But how much faster does thin ice lose thickness to the same melting energy than thicker ice exposed to the same melting conditions? 

      The Thorndike 1975 ice thickness vs. thickness growth rate curve addresses that question for the winter ice thickening season.  I've been told that simply reversing that curve to get the response for ice thinning in the melt season is not valid.  So what is the melting season equivalent for the Thorndike 1975 ice thickness - thickness accumulation curve?
Title: Re: Basic questions about melting physics
Post by: interstitial on April 21, 2020, 05:12:18 PM
The reason thickness is important for freezing is heat has to travel through ice to dissipate. The water below the ice freezes. Melting can occur at the surface so thickness isn't important. Younger ice which is thinner melts easier because it has more salt in it. Multiyear ice survives more freeze thaw cycles that allow salty brine pockets to be released from the ice. Albedo, rain and warm water can also play large roles.
Title: Re: Basic questions about melting physics
Post by: interstitial on April 21, 2020, 05:24:40 PM
If you really want to learn more about sea ice formation Tor in post 32 linked to an excellent but long and technical read about ice formation and different types of ice. Physical and dynamic properties of sea ice.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a256303.pdf (https://apps.dtic.mil/dtic/tr/fulltext/u2/a256303.pdf)
Title: Re: Basic questions about melting physics
Post by: kassy on April 21, 2020, 05:45:46 PM
       But what about the reverse process?  Is there a melting DD equivalent?  It seems likely that someone has measured that relationship.  A direct physical approach would be to measure ice thinning effects on blocks of sea ice of different thicknesses kept in a controlled setting and exposed to different temperature regimes.

We know the average Vol lost over a season so you could get an idea from that?

The blocks won´t really cut it. The type of meltponds make a difference, where the thick ice is, where the winds blow from etc.

I would love to see the underside of the sea ice to see how the keels are distributed.
Title: Re: Basic questions about melting physics
Post by: Glen Koehler on April 22, 2020, 03:25:54 AM
If you really want to learn more about sea ice formation Tor in post 32 linked to an excellent but long and technical read about ice formation and different types of ice. Physical and dynamic properties of sea ice.
https://apps.dtic.mil/dtic/tr/fulltext/u2/a256303.pdf (https://apps.dtic.mil/dtic/tr/fulltext/u2/a256303.pdf)
      Thanks interstitial!  Gow and Tucker 1991 is a classic document, the kind of comprehensive review I love.  I have only skimmed it so far, but already see numerous nuggets that address a variety of questions that have recently been discussed on various ASIF threads, including BOE estimates, land-fast ice ridging, FYI vs MYI, Fram export, and my question about the effect of thinning on melt sensitivity.

      Published in 1991 and based on many observations in the 1980s, reading what these scientists saw in their field studies is haunting.  Peter Wadhams' work is cited 14 times for 10 different papers in the review.  On 7 of those papers he was lead author.  Wadhams has been criticized lately for overstating the imminence of Arctic degradation.  Looking through this wonderful review I felt an emotional attachment to him, and understand his perspective better. 

      The Arctic those folks studied is becoming a distant memory.  They describe the characteristics of thick MYI that could hardly be found anymore.  One especially evocative statement is about what kind of change in the system would be required to melt out the Arctic, and that such a thing could only happen if atmospheric CO2 levels went to unprecedented levels.  And 29 years later, their extreme scenario is our current world.  No wonder Wadhams is freaked out.  If we knew as much about it as he does and had his historical perspective, we'd be more freaked out too. 

      That is one of the unique qualities of climate change.  With most of the scientific issues with which I become familiar professionally or personally, the more you learn, the more complexity, gray areas and nuance you discover.   So your opinion becomes less definitive.  That is why scientists so often speak in qualified terms, sometimes to the frustration of people who just want a simple yes/no black/white answer.  With climate change, for me at least, (but I think most other people who dig into it), the more you learn the more alarmed you get.  Sometimes to the point that you look around and wonder how life can go on looking so "normal" (at least until COVID-19 hit) when the planet is on fire. 

     God bless Peter Wadhams  Even if his BOE predictions were a bit early, when you see the depth of knowledge that he, Gow, Tucker and that generation of scientists developed back when the tools were much less powerful than today, you can better understand why seeing what has happened to the Arctic over the past 30 years would cause them to be alarmed.

Title: Re: Basic questions about melting physics
Post by: uniquorn on April 22, 2020, 12:01:26 PM
Quote
The Arctic those folks studied is becoming a distant memory.

There are 10 active thermistor buoys (https://data.meereisportal.de/gallery/index_new.php?active-tab1=method&buoytype=TB&region=all&buoystate=active&expedition=MOSAiC&buoynode=all&submit3=display&lang=en_US&active-tab2=buoy) in the arctic today in ice that is just about to start melting. What an opportunity to look at near real time data yourself (https://forum.arctic-sea-ice.net/index.php/topic,3013.0.html).
Title: Re: Basic questions about melting physics
Post by: interstitial on April 22, 2020, 06:57:51 PM
      Thanks interstitial!  Gow and Tucker 1991 is a classic document, the kind of comprehensive review I love.  <snip>
Your welcome. I found it useful as well that is why I remembered it.
Title: Re: Basic questions about melting physics
Post by: oren on June 04, 2020, 02:59:17 PM
This would be a good thread to discuss bottom melt mechanics.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 04, 2020, 03:03:01 PM
One thing I was thinking while reading was that we tend to forget bottom melt, and focus on top melt from all sorts of different causes, insolation and WAA, stormy weather, rain and condensation.

But I seem to remember reading a paper saying that top- and bottom melt follow each other in magnitude, so that e.g. 2012 saw both rapid top melt and unusually strong bottom melt and that the same pattern is repeated in other years - sluggish top melt coinciding with slow bottom melt and vice versa.

I can't remember where i saw this, perhaps it rings a bell with somebody else, but I don't really see where the variation in bottom melt should come from. Is there a causal link between the two, i.e. does increased top melt cause increased bottom melt? Or is there a shared external cause?

I'm sure there are lots of people here who knows a lot more than I do about this, it surely would tickle my knowledgebone to hear from some of them!
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 04, 2020, 03:07:31 PM
In short bottom melt is affected by:
* Core ice temperatures, which go up in partial correlation with top melt. AFAIK significant bottom melt can happen before significant top melt.
* Insolation transmitted through the ice, which goes up in correlation with top melt
* Movement of the ice, due to various processes at the ice-water interface.

Off the top of my layman's head, ice that moves through water, especially when there is a lower ice concentration and open water between the floes, melts faster - because of the increased energy transfer, because the cold fresh water below the ice is replaced, and because of some Ekman pumping.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 04, 2020, 03:15:10 PM
Some of the papers that I looked at through the links in the (somewhat dubious?) paper that Phoenix linked to seems to indicate that insolation through the ice is the major source of bottom melt, although those papers were written in the late noughties when ice movement was much less pronounced than it is now.

Ekman pumping from movin ice may well be a growing factor, a chilling thought when you consider that Polarstern drifted at double the speed expected. I wonder how big the effect is of this increased movement, perhaps the halocline is under severe attack? Or perhaps not?
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 09, 2020, 11:22:59 PM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?
Title: Re: Basic questions and discussions about melting physics
Post by: wili on June 09, 2020, 11:26:51 PM
No expert here, but isn't this what is meant by snow having an insulating value, at least within that narrow range?
Title: Re: Basic questions and discussions about melting physics
Post by: Aluminium on June 09, 2020, 11:45:52 PM
Colder ice probably should prevent melting. Otherwise sea ice will melt under snow. After it, snow will melt in salt water.
Title: Re: Basic questions and discussions about melting physics
Post by: uniquorn on June 10, 2020, 12:38:02 AM
we have some data.. (https://data.meereisportal.de/download/buoys/2020T75_300234068325170_TEMP_proc.csv) at least 10 Tbuoys every day for a while (https://data.meereisportal.de/download/buoys/)
air temps left, ocean temps right, snow/ice in between
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 04:57:29 AM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?

I think the sea ice melting point is actually 0C. The freezing point which is -1.8C at an average salinity. At higher salinity, the freezing point goes down.

My understanding is that sea water has a lower freezing point because extra energy is required to remove the salt ions from the solution. The result is fresh water ice + salty brine.

Going in the other direction, the ice is fresh water and the melting point is the usual 0C.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 07:05:27 AM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?

I think the sea ice melting point is actually 0C. The freezing point which is -1.8C at an average salinity. At higher salinity, the freezing point goes down.

My understanding is that sea water has a lower freezing point because extra energy is required to remove the salt ions from the solution. The result is fresh water ice + salty brine.

Going in the other direction, the ice is fresh water and the melting point is the usual 0C.
Common misconception, or rather simplification. Newly formed sea ice is not fresh but contains quite a lot of small brine pockets which will quickly start to melt the surrounding ice as the temperature approaches the melting point at that level of salinity (which is actually quite high within the brine pockets in fresh ice)

The older the ice, the purer it gets, and multiyear ice is pure enough that it will not taste salty when melted, but new ice is very salty when melted. Snow deposited on fresh ice will probably retard the salt expulsion due to insulation.

Given the size of the arctic and the ongoing freezing process whenever open water appears during winter, as well as the dearth of multiyear ice, it is probably truer to say that the average melting point is somewhere below 0 degrees, but by how much presumably depends on location and circumstances.

The two plateaus in the DMI 80N graph are interesting in thic context. It is tempting to interpret the -3C plateau as being when the temps hit the melting point of the freshest and briniest ice. And the -0.5C second plateaus when it hit the "normal" melting point. I don't remember seeing such plateaus before, an indication perhaps of much earlier melt than usual.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 07:16:07 AM
Speaking of temperature plateaus, since rental cars started having outside temperature displayed in the dashboard, I've noticed that temperatures with snow on the ground will tend to stick at 0C for days on end.
Title: Re: Basic questions and discussions about melting physics
Post by: interstitial on June 10, 2020, 07:17:30 AM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?

I think the sea ice melting point is actually 0C. The freezing point which is -1.8C at an average salinity. At higher salinity, the freezing point goes down.

My understanding is that sea water has a lower freezing point because extra energy is required to remove the salt ions from the solution. The result is fresh water ice + salty brine.

Going in the other direction, the ice is fresh water and the melting point is the usual 0C.
Common misconception, or rather simplification. Newly formed sea ice is not fresh but contains quite a lot of small brine pockets which will quickly start to melt the surrounding ice as the temperature approaches the melting point at that level of salinity (which is actually quite high within the brine pockets in fresh ice)

The older the ice, the purer it gets, and multiyear ice is pure enough that it will not taste salty when melted, but new ice is very salty when melted. Snow deposited on fresh ice will probably retard the salt expulsion due to insulation.

Given the size of the arctic and the ongoing freezing process whenever open water appears during winter, as well as the dearth of multiyear ice, it is probably truer to say that the average melting point is somewhere below 0 degrees, but by how much presumably depends on location and circumstances.

The two plateaus in the DMI 80N graph are interesting in thic context. It is tempting to interpret the -3C plateau as being when the temps hit the melting point of the freshest and briniest ice. And the -0.5C second plateaus when it hit the "normal" melting point. I don't remember seeing such plateaus before, an indication perhaps of much earlier melt than usual.

The salinity of surrounding ocean water can also have an effect. It may be fresher during melt season but it will still lower the liquid solid phase change temperature compared to pure water.
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 08:45:09 AM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?

I think the sea ice melting point is actually 0C. The freezing point which is -1.8C at an average salinity. At higher salinity, the freezing point goes down.

My understanding is that sea water has a lower freezing point because extra energy is required to remove the salt ions from the solution. The result is fresh water ice + salty brine.

Going in the other direction, the ice is fresh water and the melting point is the usual 0C.
Common misconception, or rather simplification. Newly formed sea ice is not fresh but contains quite a lot of small brine pockets which will quickly start to melt the surrounding ice as the temperature approaches the melting point at that level of salinity (which is actually quite high within the brine pockets in fresh ice)


If one were to zoom in with a powerful enough microscope, they would see that the ice and the brine are discrete entities.

In liquid state, sea water is H2O molecules bound by hydrogen bonds (intermolecular bonds) with salt ions (Na+ and Cl-) dissolved in solution.

During the freezing process, the salt ions and some of the H2O molecules are separated from the rest of the H2O molecules. The crystal lattice of ice is composed of only H2O molecules bound together by intermolecular bonds. Consider this lattice to be similar to a house which is held together with wood and screws.

The brine exists in the spaces within the lattice, but is not part of the lattice itself. The brine is like a sofa inside a house. It fits inside the house, but it is not a component of the ice house and does not impact the strength (heat) required to dismantle the ice house.

As you indicate, the brine does exit the ice lattice over time... by escaping through the spaces in the lattice. Most of the brine exits within a year of ice formation.

The lattice portion of the ice house is the same in the Arctic as the ice in your freezer and melts at the same temperature.



Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 10:39:23 AM
A comment on the main thread got me wondering. Sea ice melting point is -1.8C while fresh snow melts at 0C. What happens when air temp is -1C and the ice is covered by a snow layer?

I think the sea ice melting point is actually 0C. The freezing point which is -1.8C at an average salinity. At higher salinity, the freezing point goes down.

My understanding is that sea water has a lower freezing point because extra energy is required to remove the salt ions from the solution. The result is fresh water ice + salty brine.

Going in the other direction, the ice is fresh water and the melting point is the usual 0C.
Common misconception, or rather simplification. Newly formed sea ice is not fresh but contains quite a lot of small brine pockets which will quickly start to melt the surrounding ice as the temperature approaches the melting point at that level of salinity (which is actually quite high within the brine pockets in fresh ice)


If one were to zoom in with a powerful enough microscope, they would see that the ice and the brine are discrete entities.

Absolutely. But the brine pockets start melting the ice as soon as the melting point of the brine/ice interface is reached, well before the melting point of the ice inside the ice crystals is reached.

EDIT: The internal temperature of the ice and the brine pockets is the same. As soon as any melting starts on the interface of the two, the temperature stops rising. So ice with brine pockets will never reach 0 degrees, yet still melt out totally.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 10, 2020, 11:00:43 AM
 I know for certain that the temperature at the ocean-ice interface is -1.8C, not 0C. So for bottom melt I'm quite clear on the answer.
It would appear that top melt when there's some snow or even meltpond cover might begin at 0C. Thus  my hypothetical -1C might melt nothing, at least for a while.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 10, 2020, 11:08:43 AM
And for those who like to look at air temps in the arctic as a sign of warming, here's another thought  (which I hope is true). Temps above wet ice/melted snow are pegged at near 0C. Any lower and the top layer starts freezing and releasing heat. OTOH above open water temps can be cooler, down to -1.8C in extreme cases, unless the water aurface has been heated by the sun.
Thus under certain conditions (cloudy?) summer air temps could be cooler over open water than over the ice.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 11:17:54 AM
I know for certain that the temperature at the ocean-ice interface is -1.8C, not 0C. So for bottom melt I'm quite clear on the answer.
I agree with you on this and should have mentioned it. But the discussion has been, as I understand it, mostly about air temperatures, starting with the hypothetical clean snow on briny ice.
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 11:52:13 AM
I know for certain that the temperature at the ocean-ice interface is -1.8C, not 0C. So for bottom melt I'm quite clear on the answer.
It would appear that top melt when there's some snow or even meltpond cover might begin at 0C. Thus  my hypothetical -1C might melt nothing, at least for a while.

The ocean / ice interface is a dynamic place with respect to freezing temperatures. As the freezing season goes on and the wet side of the interface becomes saltier with brine leaking, the freezing point goes down below -1.8C. The ice side of the interface is irrelevant in terms of freezing temperature (it's already frozen).

The flip side of this occurs during the melting season when only the ice side of the interface is relevant as the water/brine below is already in liquid state. Here, the melting point is 0.0C at normal atmospheric pressure or 760 torr. Small deviations in pressure as the water gets deeper will result in slightly different melting points.

You can see that the NSIDC takes care to mention only the freezing point of sea water is -1.8C. You might try to find a credible reference anywhere on the internet which supports a melting point of the same temperature.

https://nsidc.org/cryosphere/seaice/index.html

To illustrate the impact of salinity on freezing point, here is a study which demonstrates the freezing point of Dead Sea water to be -32C.

https://scialert.net/fulltext/?doi=jas.2005.1334.1339
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 12:48:00 PM
The flip side of this occurs during the melting season when only the ice side of the interface is relevant as the water/brine below is already in liquid state. Here, the melting point is 0.0C at normal atmospheric pressure or 760 torr. Small deviations in pressure as the water gets deeper will result in slightly different melting points.

The brine below the ice controls at what temperatures bottom melt starts.

The brine within the ice controls at what temperatures melting starts within the ice and at the surface of the ice.

As long as bottom melt is active, the temperature is pegged at the melting point of the ice/water interface - which as oren pointed out is at -1.8, since any expelled brine from the freezing process quickly dissipates.

Thermal radiation enters the ice from above and in new and first-year ice, brine pockets within the ice warm up at the same rate as the ice itself. As soon as the ice starts melting at the interfaces of the brine pockets and the surrounding ice, the temperature STOPS RISING. All the extra heat (energy) is used to melt the ice.

Since the brine pockets can quite easily be saltier than the underlying ocean, the resulting starting melting point could quite well be as low as -3 degrees or even lower. As melting progresses, the brine pockets increase in size and their salinity goes down, raising the melting point.

BUT the temperature within the ice never goes above the melting point of the active melting interface. So if the ice contains brine pockets, the temperature of the ice never reaches 0C. Which makes it very obviously wrong to say that the melting point of that ice is 0C.

What about the surface, I hear you ask. We've covered bottom melt and "internal" melt, which is what happens as a result of thermal radiation (i.e. sunlight). Melting caused by conduction from air takes place at the surface, but again, the brine pockets reach all the way to the surface. So the melting ice will always be interacting with brine, and thus melting of the surface will start when air temperatures are at the melting point of the brine-pocket/ice interface.

So all in all, Phoenix, new sea ice has a melting point well below 0, first year ice also has a melting point below 0 but not by much, and multiyear ice has a melting point at 0.

The reason that you will not find any direct information online about the melting point of sea ice is that it is never simple nor obvious (as opposed to the freezing point of sea water).
Title: Re: Basic questions and discussions about melting physics
Post by: SimonF92 on June 10, 2020, 01:15:17 PM
Might explain why we've been having a really tough time pinning down our "ice:ocean" interface recently.

We've been observing very strange fluctuations in temperature at the bottom of the ice in the raw data, which is bugging the code we used to make;

www.mosaic-ice.com:8501



The raw data can be viewed here;

https://data.meereisportal.de/gallery/index_new.php?lang=en_US&active-tab1=method&active-tab2=buoy&singlemap&buoyname=2019T56
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 01:38:30 PM

So all in all, Phoenix, new sea ice has a melting point well below 0, first year ice also has a melting point below 0 but not by much, and multiyear ice has a melting point at 0.

The reason that you will not find any direct information online about the melting point of sea ice is that it is never simple nor obvious (as opposed to the freezing point of sea water).

I agree that multiyear ice has a melting point of 0 at 1 atm pressure. Let's just agree to disagree on the variability of melting point with ice age. If you have links to respected sources which support that version, I'll be happy to look at them.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 01:48:47 PM

So all in all, Phoenix, new sea ice has a melting point well below 0, first year ice also has a melting point below 0 but not by much, and multiyear ice has a melting point at 0.

The reason that you will not find any direct information online about the melting point of sea ice is that it is never simple nor obvious (as opposed to the freezing point of sea water).
I agree that multiyear ice has a melting point of 0 at 1 atm pressure. Let's just agree to disagree on the variability of melting point with ice age. If you have links to respected sources which support that version, I'll be happy to look at them.

This is what we call common sense + a longstanding interest in the physics of ice.

I did a very quick web search at the beginning of this conversation, "melting point of ice",  I just did it again now, here is a quote from the very first page suggested by Google:

Quote from: NSIDC link=https://nsidc.org/cryosphere/seaice/index.html
New ice is usually very salty because it contains concentrated droplets called brine that are trapped in pockets between the ice crystals, and so it would not make good drinking water. As ice ages, the brine eventually drains through the ice, and by the time it becomes multiyear ice, nearly all of the brine is gone. Most multiyear ice is fresh enough that someone could drink its melted water. In fact, multiyear ice often supplies the fresh water needed for polar expeditions. See Salinity and Brine in the Characteristics section for more information.

Pure common sense tells you that ice that tastes salty when melted does not have a 0C degree melting point. There is nothing to disagree about here, it's just the way things are. Ice with salt interlaced can't even reach 0C - it's physically impossible.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 10, 2020, 01:59:54 PM
Thank you for the answers. Obviously FYI melting point is not 0C, I'll take binntho's description.
In any case, no need for further back and forth, unless someone else wants to step in with additional info.
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 02:44:01 PM
Thank you for the answers. Obviously FYI melting point is not 0C, I'll take binntho's description.
In any case, no need for further back and forth, unless someone else wants to step in with additional info.

It would be nice if you didn't use the word "obviously" here. It is a way of saying that you are obviously right and i am obviously wrong which is a form of one upsmanship at the same time you are basically telling me to shut up which is an example of authority silencing dissenting perspectives.

We can agree to disagree politely.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 10, 2020, 02:56:37 PM
Thank you for the answers. Obviously FYI melting point is not 0C, I'll take binntho's description.
In any case, no need for further back and forth, unless someone else wants to step in with additional info.

It would be nice if you didn't use the word "obviously" here. It is a way of saying that you are obviously right and i am obviously wrong which is a form of one upsmanship at the same time you are basically telling me to shut up which is an example of authority silencing dissenting perspectives.

We can agree to disagree politely.
Is this an example of what they call microagression? I don't know. But claiming that people can agree to disagree in factual discussions is just rubbish. There are no dissenting perspectives when it comes to physics. And obviously oren is free to use his authority to tell us to shut up. I can even hear him shouting while reading this, so I'm shutting up now with immediate effect!  8)
Title: Re: Basic questions and discussions about melting physics
Post by: oren on June 10, 2020, 03:08:45 PM
After reading the responses, it is obvious - to me. I am fine with agreeing to disagree as long as the back and forth is over.
Title: Re: Basic questions and discussions about melting physics
Post by: Phoenix on June 10, 2020, 03:29:50 PM
After reading the responses, it is obvious - to me. I am fine with agreeing to disagree as long as the back and forth is over.

OK, if you want to stay with the word obvious, I will leave it on the same terms and say that it is obvious to me that you and binntho are wrong.
Title: Re: Basic questions and discussions about melting physics
Post by: Phil. on June 10, 2020, 05:59:11 PM

If one were to zoom in with a powerful enough microscope, they would see that the ice and the brine are discrete entities.

In liquid state, sea water is H2O molecules bound by hydrogen bonds (intermolecular bonds) with salt ions (Na+ and Cl-) dissolved in solution.

During the freezing process, the salt ions and some of the H2O molecules are separated from the rest of the H2O molecules. The crystal lattice of ice is composed of only H2O molecules bound together by intermolecular bonds. Consider this lattice to be similar to a house which is held together with wood and screws.

The brine exists in the spaces within the lattice, but is not part of the lattice itself. The brine is like a sofa inside a house. It fits inside the house, but it is not a component of the ice house and does not impact the strength (heat) required to dismantle the ice house.

As you indicate, the brine does exit the ice lattice over time... by escaping through the spaces in the lattice. Most of the brine exits within a year of ice formation.

The lattice portion of the ice house is the same in the Arctic as the ice in your freezer and melts at the same temperature.

As one who in my chemistry career used salt-ice baths to achieve lower than 0ºC temperatures I wish to correct the physical chemistry referred to in this post.

When water freezes into ice, the hydrogen bonds make a hexagonally shaped network of molecules inherent to the structure of ice.
When a solute is added to water the ordering of the solvent molecules is disrupted. This means that more energy must be removed from the solution in order to freeze it.
When salt is added to water, the resulting ions in the water disrupt the usual network of hydrogen bonds made upon freezing. As a result, the freezing point of the solution is lower than it is for the pure solvent. This is termed freezing point depression.  As the ice warms up the network of hydrogen bonds (referred to above as the lattice) requires less energy to be broken up so the melting point is lower.
Because the solubility of the salt decreases with temperature some of the salt is rejected, forming brine pockets.  These brine pockets get eliminated over time but some salt remains in the ice disrupting the structure. In multiyear ice the salt content will ultimately reach the solubility of the lowest temperature the ice has reached so in thick MYI you'd expect lower salinity at the top vs. the bottom.

Here's an amusing video illustrating the difference in melting between saline and pure water ice.

https://www.youtube.com/watch?v=PRxpWArwavk
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on June 11, 2020, 03:47:45 AM
     Inside Climate News article on aerosol drop impact on Arctic sea ice
https://insideclimatenews.org/news/08062020/sulfate-emissions-coronavirus-arctic-heatwaves (https://insideclimatenews.org/news/08062020/sulfate-emissions-coronavirus-arctic-heatwaves)

     "Overall, this winter wasn't particularly warm, but now that's flipped around in the last month and we're really seeing the effects," says Mark Serreze, director of the National Snow and Ice Data Center (NSIDC). "Big holes are opening up along the Siberian coast where it's been the warmest."

     "This Central Arctic heatwave may not be a one-off event only occurring in spring 2020, researchers suggest. Rather, if levels of global industrial air pollutants continue to fall due to the Covid-19 pandemic, the current Arctic warmth could be a bellwether of what's to come later this summer when sea ice melt annually kicks into high gear."

     "Indeed, in a 2017 study, scientists posited that the sulfate aerosols released due to human activity masked the decline in Arctic sea ice in the mid-20th century, before the Clean Air Act went into effect, and actually led to periods of ice growth."

     "Using earth system computer modeling, his simulations showed that sulfate aerosol reductions in Europe since 1980 could potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic received approximately 0.3 watts per meter squared of energy, warming by 0.9 degrees Fahrenheit on average as Europe's sulfur emissions declined."

     " "We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and the Arctic climate are inherently linked," his 2016 Nature Geoscience study stated. "
Title: Re: Basic questions and discussions about melting physics
Post by: Freegrass on June 11, 2020, 04:59:37 AM
Great article Glen. It has already been discussed here that aerosol reduction has a warming effect in summer, but a cooling effect in winter. Is that why the antarctic sea ice extent is close to normal this season?


(https://nsidc.org/data/seaice_index/images/daily_images/S_iqr_timeseries.png)
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on June 11, 2020, 03:37:31 PM
Hi FG - My guess (and that is all it is) is that aerosol reduction could also cause increased radiation losses out to space during the winter as the aerosols can also add to the insulating effect of the atmosphere, thus fewer particles = less insulation = more winter heat loss. 

      During the 24 hour nights of polar winter there is no counteracting cooling effect of aerosol particles reflecting incoming shortwave radiation.  So the cooling effect, which dominates during summer is not active during winter.

      But I don't pretend to understand the details of these interactions, just thought I'd take a shot it since you asked.  It would be great to get an answer from somebody who studies this stuff.
 
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on June 11, 2020, 03:51:46 PM
I think it more of the vast expanse of cold that makes the difference.  What little effect the aerosols have is meaningless, when temperatures are consistently below freezing.  Even the coastal areas average daily below freezing temperatures year round.
Title: Re: Basic questions and discussions about melting physics
Post by: Freegrass on June 11, 2020, 08:44:09 PM
It would be great to get an answer from somebody who studies this stuff.
I agree, but it looks like nobody is home today...  :(
Title: Re: Basic questions and discussions about melting physics
Post by: uniquorn on June 13, 2020, 10:00:15 PM
Some Mosaic Tbuoy (https://data.meereisportal.de/gallery/index_new.php?active-tab1=method&buoytype=TB&region=all&buoystate=active&expedition=MOSAiC&buoynode=all&submit3=display&lang=en_US&active-tab2=buoy) charts showing overlays of temperature profiles through the ice from jun1-13
click to run ~1.5MB

Air where the lines diverge on the left.
Then snow or melt ponds?  T56, T68 and T75 reach +3C close to ice surface.
Ice is the thickening band in the middle but that is the temperature profile changing as it slowly warms. The thickness is calculated from the number of thermistors along the x-axis. Multiply by 2 as they are 2cm apart.
ocean on the right.

images where you can read the dates are here (https://forum.arctic-sea-ice.net/index.php/topic,2906.msg268474.html#msg268474)

static image of T56 (https://data.meereisportal.de/download/buoys/2019T56_300234065176750_TEMP_proc.csv) with close look at the ice/ocean interface
Title: Re: Basic questions and discussions about melting physics
Post by: uniquorn on June 14, 2020, 09:57:26 PM
I'm struggling to interpret the charts above. Thought this may be helpful here

On the thermodynamics of melting sea ice versus melting freshwater ice (https://www.cambridge.org/core/journals/annals-of-glaciology/article/on-the-thermodynamics-of-melting-sea-ice-versus-melting-freshwater-ice/B88EBD53A0209295EA0662825C48EBAE)
Wiese, M., Griewank, P., & Notz, D. (2015). On the thermodynamics of melting sea ice versus melting freshwater ice. Annals of Glaciology, 56(69), 191-199. doi:10.3189/2015AoG69A874
Quote
The timespan needed to warm freshwater ice is much shorter than for sea ice, because we actually completely transform the sea ice into water by heating the ice to its liquidus temperature. This is also the reason why the calculation gives a longer time for the warming of the ice with a lowerbulk salinity: the ice has a higher solid fraction, which needs more energy to be completely changed into liquid.
Becausethe typical timescale for the heating of the sea ice is much longer than the diffusive timescale of ~3 hours, the temperature profile during the heating will no longer be linear(seeFig.3). Instead, we expect a temperature minimum in the interior of the ice, which indeed we find both in the experiments and in the simulations. This implies that we can no longer roughly separate an initial period of warming of the ice from a consecutive period of thinning of the ice, as was the case for freshwater ice. For sea ice, the ice still keeps warming significantly in its interior as the surface is already at its liquidus temperature (cf. blue lines in Fig. 1).
This slow heating of the ice’s interior explains the initial shape of the observed and modelled evolution of the melt rates that is shownin Figure2c and d: as the ice’s interior gets warmer during the heating,the heat flux into the ice’s interior becomes smaller. Therefore, more energy remains available to thin the ice at the bottom and at the surface, which explains the initial increase in melt rate. Compared to freshwater ice, the initial melting is slower because more energy is used to warm the interior of the sea ice and to decrease its solid fraction. At later stages, however, this initial investment of energy pays off, and the by then much less solid sea ice thins faster than freshwater ice. To understand why the thinning of the sea ice eventually slows down again, we need to consider the vertical inhomogeneity of the bulk salinity within the ice. Since we do not have direct measurements of bulk salinity available, we use for our analysis the simulated bulk salinity evolution shown in Figure4.
The simulations show clearly that after the onset of surface warming, flushing sets in, which transports cold and salty brine from higher up in the ice to the region close to the ice–ocean interface. Heat diffusion from the ice–ocean interface into the ice and the negative heat advection of the cold flushing brine cools the lower layers for a short time after the onset of melting. This cooling keeps the highly saline lowest layers with a low solid fraction from being melted away by the oceanic heat flux.In the 12 gkg^-1 simulation the sum of the diffusive heat flux from the ice–ocean interface and the negative heat advection of the cold brine is stronger than the oceanic heat flux, which causes some ice to grow at the ice–ocean interface(Fig.4).
However, once the heat flux from the interior ice is depleted, a relatively rapid bottom ablation occurs, since only ice with a comparably low solid fraction needs to be completely dissolved to thin the bottom ice. This initially slow melt followed by a rapid thinning is visible in all sea-ice experiments and simulations(Fig. 2).
Quote
Once the salty layer at the bottom is fully eroded, bottom ablation slows down significantly, since then ice with a much higher solid fraction is present at the ice-ocean interface. For example, ice grown in water with an initial water salinity of 28 gkg-1 has a very low bulk salinity close to 0gkg-1 about 95 hours after the start of the experiment and the bottom ablation decreases from this moment on (Fig. 4). It is primarily this decrease in bottom ablation that causes the observed and modelled slowdown of the thinning after the initial acceleration. This process is amplified by the fact that flushing continues to very effectively desalinate the ice, which is seen in the almost complete loss of bulk salinity in the simulations as time progresses. Hence, the solid fraction of the remaining ice becomes higher and higher, making it more and more difficult to thin that remaining ice. The melt rates of the sea ice therefore approach those of freshwater ice towards the end of the experiment, both in the laboratory and in the numerical model. In line with expectations, we always find that sea ice is fully melted faster than freshwater ice, because sea ice has a lower overall solid content and hence requires less time to melt for any given heat flux than the fully solid freshwater ice.
Quote
For all experiments, ice was grown to a thickness of 0.1 m at a temperature of -20°C. Once that thickness was reached, the air temperature was either increased directly to +10°C or increased stepwise to simulate a slower transition from freezing to melting conditions.
So perhaps not entirely relevant to 1.5m sea ice but should cover two bottles of ice in a cooler.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on June 15, 2020, 04:42:35 AM
very interesting!
Title: Re: Basic questions and discussions about melting physics
Post by: Tor Bejnar on June 15, 2020, 06:17:30 PM
Indeed!  While the graphs are 'above my pay grade', the explanations were fully within my grasp.
Title: Re: Basic questions and discussions about melting physics
Post by: Freegrass on June 17, 2020, 08:41:15 AM
It would be great to get an answer from somebody who studies this stuff.
I agree, but it looks like nobody is home today...  :(
Is anyone seeing this?

(https://nsidc.org/data/seaice_index/images/daily_images/S_iqr_timeseries.png)
Title: Re: Basic questions and discussions about melting physics
Post by: Human Habitat Index on June 17, 2020, 08:59:49 AM
Anecdotally we have had clear unusually chilly nights in southern Australia, consistent with the effect of less aerosols in the atmosphere.
Title: Re: The 2020 melting season
Post by: Phoenix on July 07, 2020, 09:13:36 AM

I can feel freezing in winter when standing in the shadows, and then walk out into the sunshine and start feeling warmer after just a few seconds.  The air has not got any warmer (and BTW I doubt I would be able to tell the difference between .5C or 2C).  But I do know that the sunlight hitting my jacket and pants and skin and hat is being converted to heat and the effect is considerable, despite the uniform coldness of the air around me..

Take two full and frozen ice cube trays out of your freezer. Put one in your refrigerator which might be cooled to 5C and shut the door so its dark inside. Take the other tray and put it a dark space like a closet which is at room temperature, say 23C or so. Check on them both after an hour.

Light (or lack thereof) is constant. Both are above 0C and will melt. Will they melt at the same rate ? No. The tray in your closet will melt faster.

Your personal example of stepping out of the shade is not reliable because your body sensors can't easily differentiate between the simultaneous experience of direct solar radiation and thermal radiation emitted from the sun baked earth you are now moving over.



Title: Re: Re: The 2020 melting season
Post by: pleun on July 07, 2020, 09:18:24 AM

Light (or lack thereof) is constant. Both are above 0C and will melt. Will they melt at the same rate ? No. The tray in your closet will melt faster.

Yet the temperature just above the icecubes will be the same in both cases. You just took down your own argument...
Title: Re: Re: The 2020 melting season
Post by: El Cid on July 07, 2020, 09:24:39 AM
Take two full and frozen ice cube trays out of your freezer. Put one in your refrigerator which might be cooled to 5C and shut the door so its dark inside.

And now take that ice cube and put it out into the full sun. See what happens. And how fast
Title: Re: Basic questions and discussions about melting physics
Post by: oren on July 07, 2020, 01:33:08 PM
To whom it may concern, let it be known. A large region of sea ice will keep surface air temperatures pegged near the melting point, due to the energy soaked up by the phase change of ice into water. Thus surface air temperatures are often not very informative during the Arctic summer.
Title: Re: Basic questions and discussions about melting physics
Post by: Tony Mcleod on July 07, 2020, 02:05:09 PM
To whom it may concern, let it be known. A large region of sea ice will keep surface air temperatures pegged near the melting point, due to the energy soaked up by the phase change of ice into water. Thus surface air temperatures are often not very informative during the Arctic summer.

These anomaly graphs http://ocean.dmi.dk/arctic/meant80n_anomaly.uk.php (http://ocean.dmi.dk/arctic/meant80n_anomaly.uk.php) clearly show how Arctic temps have climbed in autumn, winter and spring but have been flat as a pancake in summer.
Title: Re: The 2020 melting season
Post by: Phoenix on July 07, 2020, 05:24:49 PM

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics (https://en.wikipedia.org/wiki/Melting_point#Thermodynamics) -

Attached is the latest DMI 80N temperature chart. It shows the 2m temps coming down from an above normal peak. The forecast calls for a further decline in a few days. If it's not clear, I'm referring to temps at 2m, not at 0m.

http://ocean.dmi.dk/arctic/meant80n.uk.php
Title: Re: Re: The 2020 melting season
Post by: sedziobs on July 07, 2020, 05:33:29 PM
Attached is the latest DMI 80N temperature chart.
This chart tells us next to nothing about energy transfer to ice, especially under high pressure.
Title: Re: Re: The 2020 melting season
Post by: igs on July 07, 2020, 06:30:56 PM

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics (https://en.wikipedia.org/wiki/Melting_point#Thermodynamics) -

Attached is the latest DMI 80N temperature chart. It shows the 2m temps coming down from an above normal peak. The forecast calls for a further decline in a few days. If it's not clear, I'm referring to temps at 2m, not at 0m.

http://ocean.dmi.dk/arctic/meant80n.uk.php (http://ocean.dmi.dk/arctic/meant80n.uk.php)

It's not relevant at this time of the year and current conditions. More info would be too long to read but you can find it if you search for DMI and for DMI above 80N especially.

DMI is special in itself somehow and DMI above 80N in Summer has been discussed and explained dozens if not hundreds of times.

On of the best chances to find such entries other than using a search tool ist in the melting season threads of each year in posts ranging from 15. of June to the end of July.

Also i think i remember there is a DMI above 80N thread somewhere, just in case you're interested to find info WHY it is as it is  ;)
Title: Re: Re: The 2020 melting season
Post by: Viggy on July 07, 2020, 06:54:37 PM

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics (https://en.wikipedia.org/wiki/Melting_point#Thermodynamics) -

Attached is the latest DMI 80N temperature chart. It shows the 2m temps coming down from an above normal peak. The forecast calls for a further decline in a few days. If it's not clear, I'm referring to temps at 2m, not at 0m.

http://ocean.dmi.dk/arctic/meant80n.uk.php

What exactly is the value of this insanity? Temperature at 0m is the around 0C (in the summer) because there is ice at 0m.

Temperature at 2m is close enough to the ice to be anchored around a very tight range around 0C during the summer months. You clearly know and understand this based on previous posts. Yea, there may be tiny fluctuations but there is absolutely zero analytical value in looking at a snapshot of 1 week and calling peaks and declines.

Stop attempting to derail constructive conversation because you are bored at home during Covid or whatever your affliction is.
Title: Re: Basic questions and discussions about melting physics
Post by: jens on July 14, 2020, 09:36:20 AM
I have no idea into which topic to post this, but in some topics (forgot which one) there was discussion about how strongly preceding winter influences the melting season. It looks like it has most influence on the early season melting, with gradually diminishing effect during the year. There was one chart which showed that temperature-wise 2016 had the warmest winter and subsequently 2016 has been duly leading in May and June. However, it lost its advantages, when the effects of summer weather have kicked in.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on July 14, 2020, 01:27:56 PM
A really good (cold, little export) winter can give extra ice, and of course the opposite is true for a bad winter. OTOH a really bad summer (warm, sunshine, export) can take away extra ice and cause deficit, while a good summer will do the opposite. Which one of these wins over the other depends on the magnitude, so there can be no definitive answer.
What has already been proven is that a very cold or warm winter is no guarantee of the summer minimum - 2012 had high volume in March, while 2017 had the lowest volume ever. But at the end of summer their roles were reversed.
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on July 21, 2020, 05:04:22 AM
     Does anybody care to disabuse me of my conjecture that there is a nonlinear relationship between ice thickness and melt resistance - with decrease in melt resistance curving down faster than the linear % decline in thickness - due to qualitative differences in thinner vs. thicker ice?

     The fact that ice accumulation is radically nonlinear with increasing thickness is accepted as established fact, e.g. the curve published by Thorndike 1975
(https://ag-radar2.umaine.edu/memodel/Thorndike-ice-thickness-freeze-rate-chart.png).

     Earlier this year I pitched the idea that the reverse is true for melting, with 1 meter thick ice melting at twice the rate of 2 meter ice (0.8 cm/day vs. 0.4 in the example shown):  (https://ag-radar2.umaine.edu/memodel/Reversed-Thorndike-thin-ice-chart.png).

     Those who actually understand the physics of ice melt shot down that theory, explaining that the energy flows involved in summer melt are not simply the reverse of winter freeze.  Correction which I gratefully accept, .... but

     ....even if a straight reversal of the thickness-freeze rate curve to estimate thickness-melt rate curve is too simplistic to be valid, that still leaves open the possibility, and (in my mind at least) the near certainty that the melt rate vs. thickness ratio is not a stricltly linear 1:1 ratio.  I have no idea what it would be, but it I'm almost certain that the melt rate for 1 meter vs. 2 meter thick ice has to be greater than 1:1.  And that ratio has to be even greater for 0.9, 0.8, 0.7 etc. meter thick ice vs 2 meter ice. 

      It is well documented and accepted that the chemical and structural characteristics of Arctic sea ice varies with thickness.  Those qualitative differences have to make some difference to the melt rate. 

      This is not merely an academic question.  An accelerating melt rate with declining thickness would have major consequence for acceleration of Extent and Volume losses as average thickness continues to decline as shown on the chart posted by gerontocrat at https://forum.arctic-sea-ice.net/index.php/topic,119.msg275579.html#msg275579 (https://forum.arctic-sea-ice.net/index.php/topic,119.msg275579.html#msg275579)  (A chart which I nominate for the ASI Graphical Hall of Fame).

      Which leads to a vision of the near future of the ASI showing accelerated melt to the same weather conditions and energy inputs of previous years, and even more so as continued cumulative global warming, exacerbated by Arctic amplification, increases energy inputs into melt seasons and reduces winter refreeze potential (and greater potential for Arctic cyclones, and jet stream weakening to allow warm air mass incursions, etc.). 

      If so, the drop from 4 million km2 September Extent to 3 million could occur in a shorter time frame than the observed trend for the drop from 5 million to 4 million.  And with average ice thickness in late summer approaching 1 meter, a nonlinear melt response for thinner ice would  accelerate even more for the drop from 3 million to 2 million km2, and even more than that for the drop from 2 million to 1 million km2. 

    (I suspect that dropping below 1 million km2 would complicate things because that final ice has resistance due to protection within bays etc. that would compensate for a thin ice melting effect).

      By extrapolation, the linear Extent decline trend reaches zero decades later than the Volume trend.  But of course that is impossible, because when there is no Volume, there is no ice left to create Exent.  So the Extent trend has to eventually start accelerating to curve downward to catch up with Volume by the date when they both reach zero.  I think that thin ice melt acceleration will be a major contributing factor (along with mobiillty for export, fracturing, surface area and possible others), that will cause that to happen.

     Is there a fallacy in this line of thinking?  What alternative mechanism accounts for the  required unification of Extent and Volume as they approach zero.  Binntho I'm talking to you!  This is right up your alley and I haven't seen you post for a while.

    One more conjecture.  I think that as the average thickness in the High Arctic Seas, as shown in gerontocrat's graph, is approaching 1 meter in September, the accelerated thin ice melt effect, which might have been relatively inconsequential until now, will become an increasingly important influence.  As a result, there will be "Extent goes poof" events of increasing scale and frequency over the next 10 years, resulting in a BOE by the early 2030s if not before.
Title: Re: Basic questions and discussions about melting physics
Post by: Steven on July 21, 2020, 12:09:24 PM
average thickness chart posted by gerontocrat at https://forum.arctic-sea-ice.net/index.php/topic,119.msg275579.html#msg275579 (https://forum.arctic-sea-ice.net/index.php/topic,119.msg275579.html#msg275579)  (A chart which I nominate for the ASI Graphical Hall of Fame).

Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.
Title: Re: Basic questions and discussions about melting physics
Post by: gerontocrat on July 21, 2020, 01:59:18 PM
Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.
I have understood that area data was badly affected by melt ponds when insolation was high in early to mid-summer, and that produced the underestimates. But I also thought I had read that this effect diminished in the late Arctic summer, (starting around now) by which time melt ponds had drained, and as insolation quickly reduced in the high Arctic, melt ponds would no longer form to any great extent. So I always thought that by the minimum, the area data was less out of wack.

And surely dividing volume by extent for thickness has the opposite problem, as it includes extent at 100% for cells that have 15% or more of ice, i.e. over-estimates actual ice area?

I have looked at some reports and they seem to say that melt ponds is one problem, and in one study I found (for Hudson Bay & East Coast of America) quotes an underestimate of 23% in June. Others refer to difficulties of the sensors to detect thin ice. 

But I cannot find a study / science paper with the 10% to 25% figure. Can you point me to it?

So, as **Wipneus stated that the PIOMAS uses NSIDC Area data as input, for the time being for me  it's "Thickness = PIOMAS Volume divided by NSIDC Area".
________________________________________________________-
** https://forum.arctic-sea-ice.net/index.php/topic,119.msg275246.html#msg275246
Title: Re: Basic questions and discussions about melting physics
Post by: Tor Bejnar on July 21, 2020, 07:01:26 PM
Glen,
Sea ice in the early part of the melting season melts more slowly than in the late part of the melting season because the ice is colder to start with, and it takes time for the ice in the middle (core) - between sea water and air - to warm.  Even after the ice surfaces start melting, 'heat' applied to the ice is partially directed to the core.  I've seen charts showing this phenomenon on these threads, but I don't recall where.

There will be other differences due to salt brine extrusion and its timing - I recall reading that sea ice (especially first year ice) has more brine before it first thaws a little, but these dynamics are too complicated for me!

Anyway, this is a little part of the answer.
Title: Re: Basic questions and discussions about melting physics
Post by: Steven on July 21, 2020, 08:34:55 PM
Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.

I have understood that area data was badly affected by melt ponds when insolation was high in early to mid-summer, and that produced the underestimates. But I also thought I had read that this effect diminished in the late Arctic summer, (starting around now) by which time melt ponds had drained, and as insolation quickly reduced in the high Arctic, melt ponds would no longer form to any great extent. So I always thought that by the minimum, the area data was less out of wack.
...
But I cannot find a study / science paper with the 10% to 25% figure. Can you point me to it?

So, as **Wipneus stated that the PIOMAS uses NSIDC Area data as input, for the time being for me  it's "Thickness = PIOMAS Volume divided by NSIDC Area".

If you had bothered to compare your thickness graph with the official PIOMAS thickness graph (http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/Bpiomas_plot_daily_heff.2sst.png), you would have noticed that your numbers are systematically too high during Summer and Autumn, by about the percentages I posted.  Even as late as November there is still a discrepancy.

PIOMAS uses NSIDC concentration as some kind of replacement for melt ponds: PIOMAS doesn't model melt ponds explicitly, but only implicitly by assimilating the NSIDC concentration data.  But that does not mean that you can divide the volume by NSIDC area to get the average thickness.

NSIDC area is useful for making predictions about the minimum (Slater, Dekker, Tealight etc).  But if you want to know the real sea ice area, you're better off using the Hamburg AMSR2 sea ice area.  It's available on Wipneus' site (https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/data).

NSIDC area underestimates the real sea ice area, not only in Summer but also in Autumn.  This was discussed several times in the Home Brew thread.  Last year I posted some graphs about this: see here (https://forum.arctic-sea-ice.net/index.php/topic,2591.msg217032.html#msg217032).  Below is a similar graph, showing the ratio of NSIDC and AMSR2 area, averaged over the past 7 years.  Looking at individual years, the daily ratio in September ranges between 0.76 and 0.91.


(https://i.imgur.com/EvMpNeu.png)
Title: Re: Basic questions and discussions about melting physics
Post by: grixm on July 21, 2020, 08:53:41 PM
Has anyone combined the PIMOAS thickness data with AMSR2 area to create a better volume measurement then?
Title: Re: Basic questions and discussions about melting physics
Post by: oren on July 21, 2020, 09:25:00 PM
Grixm - I have done it for the CAB and the ESS and posted some charts in the past in the PIOMAS thread. The data is somewhat problematic. I will make a similar chart for the whole Arctic and post it later tonight.

Steven - thanks for the very informative post.
Title: Re: Basic questions and discussions about melting physics
Post by: gerontocrat on July 21, 2020, 09:48:25 PM
Re Steven's critique...

The brick wall is that AMSR2 data starts in 2013? mid-2012?

I started looking at thickness from oversimple arithmetic, namely 75% loss of volume and 50% loss of extent since 1979 means on average thickness today half of thickness 1979.

I also wanted to separate the High Arctic from the peripheral seas, and track the reduction in thickness over decades. Data available is NSIDC extent and area back to 1979, daily volume by each sea back to 2000, and monthly average volume by each sea back to 1979 (provided by Wipneus). Hence the graphs.

Do I accept that going back to 1979 for thickness graphs is just not possible? Oren has got since 2013 sorted, so if the answer is yes, time to dump my thickness graphs into the gigo bucket 
Title: Re: Basic questions and discussions about melting physics
Post by: oren on July 21, 2020, 10:27:16 PM
Don't dump them Gero. Maybe they don't represent actual accurate thickness, but they are still informative and enable a sort of comparison between years going back much longer.
Title: Re: Basic questions and discussions about melting physics
Post by: ajouis on July 21, 2020, 10:47:05 PM
Gerontocrat I wholly agree with Oren, even if it is not perfect, more data is better than less data, especially as it helps with longterm trends, plus who knows maybe your modelisation is good enough to be picked up by the (rest of the) scientific community and will become a new standard, who knows.
Title: Re: Basic questions and discussions about melting physics
Post by: glennbuck on July 23, 2020, 12:14:31 AM
This data from 21st of July 2019 from gerontocrat was within 20,000 km^2 off the September minimum very accurate.

Title: Re: Basic questions and discussions about melting physics
Post by: Tor Bejnar on July 23, 2020, 01:44:07 AM
There has been a great deal of discussion recently about discerning/calculating ice thickness and very little discussion about melting physics.  There must be a relation between the two topics, but don't ask me to explain it!  :-\
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on July 23, 2020, 07:24:55 AM
I think we all agree, as Glen points out (https://forum.arctic-sea-ice.net/index.php/topic,2709.msg275734.html#msg275734), that the decline in extent must at some point catch up with the decline in volume. Hence the decline in extent cannot continue at its current linear rate. But will the rate of change be incremental or sudden? I.e. will the curve bend or break?

And is it somehow linked to the thickness of the ice, i.e. does the rate of melt increase with falling average thickness? The physics are not reversible, but still, the following holds true:

      It is well documented and accepted that the chemical and structural characteristics of Arctic sea ice varies with thickness.  Those qualitative differences have to make some difference to the melt rate. 

One of the important differences is to do with the core temperature of the ice. The sooner the core warms up, the faster the ice melts. And thinner ice warms up faster than thicker ice. Other differences between various thicknesses are based more on the age of the ice than the thickness per se. Brine channels, brittleness, structural strength etc. change with age rather than thickness, but then thickness also increases with age so again there is a link albeit not a direct causal link.

All in all I agree with Glen that ice melt should accelerate with decreasing thickness, but how large is this effect, and more importantly, could it be used as an explanation for the current rapid decline in ice extent?

     Is there a fallacy in this line of thinking?  What alternative mechanism accounts for the  required unification of Extent and Volume as they approach zero.  Binntho I'm talking to you!  This is right up your alley and I haven't seen you post for a while.

The Internet for the entire country was blocked for over 2 weeks, and then only activated in the capital. So I took the first plane and here I am in a hotel room, hoping to catch up on some work and instead indulging in my preferred pastime of writing on the ASI forum!

Coming back after 3 weeks and seeing the incredibly rapid melting that has taken place in July has been fairly stunning. As of today the difference between the current year and the second lowest is almost 630.000 km2 - an incredible difference.

My own view as developed over the seasons is that it is rather the amount of open water along the perifery of the ice that will be the largest contributor to accelerated fall in extent, rather than the average thickness of the ice.

Large areas of open water during maximum insolation means that a lot of extra energy enters the system, but of course only where the ice is not. A delay to refreeze rather than an accelerated melt. The second factor needed is storminess - which has been missing for all of July as far as I can gather, but which might well be picking up now. Storms move the warm waters around, bringing them to where the ice is, storms cause waves that break up the ice (and the longer the fetch, the bigger the waves), and storms late in the season probably have a positive impact on the radiative balance.

So the current situation is exactly what I would predict would accelerate melt as soon as the storms kick in. But that does not explain why we have so much open water to begin with!

Perhaps a simplification of the current situation would be to reduce it to three or four factors that combine to cause increased melt at different times - the first of course being the steadily increasing global temperature, the second being the unusually warm spring followed by a very sunny July this year, the third being the increasingly thin and fragile ice that undoubtedly melts faster than the older and thicker ice, and the final (and to my mind, increasingly important as time goes), is the amount of open water.

But for the future, in my opininon the main factor in increasing the rate of melt will be the amount of open water in the second (post max insolation) part of the melting season. A steady linear decline overall will secure the increased amount of open water up to that point, and a non-linear effect of open water + storminess will take care of the rest.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on July 23, 2020, 08:20:08 AM
Welcome back binntho. Excellent post.
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on July 23, 2020, 06:53:18 PM
Welcome back binntho. Excellent post.
+1 :)
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on July 23, 2020, 07:30:54 PM
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 

Also, the physics is reversible.  If the ice were to thicken, it would return to its previous state.
Title: Re: Basic questions and discussions about melting physics
Post by: mdoliner on July 23, 2020, 07:57:54 PM
Question about draining of melt ponds.

Floating ice is 9/10 under water. If a melt pond was deep enough to make a hole in the bottom of the flo the pond wouldn't drain any further than until the surface of the pond was at sea level. So 9/10 of it would remain. Are melt ponds shallow ponds whose bottom is above sea level that drain from the side? I find that hard to believe since the extra heat from the sun should warm the water uniformly and the only ice to melt in the center of the pond would be at the bottom.
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on July 23, 2020, 08:00:25 PM
     The only way for Volume loss trend to decline relative to Extent is for Thickness to increase.  With the net energy balance of the Arctic system already above equilibrium to maintain the current seasonal ice levels, compounded by increasing energy inputs from GHG emissions that not only continue to load the system, but still doing so at any increasing rate, I see virtually no chance for Thickness levels to increase, or for the Volume rate of decline to lessen.
Title: Re: Basic questions and discussions about melting physics
Post by: BeeKnees on July 23, 2020, 08:23:51 PM
Maybe the wrong place but I'm sure it will be moved or deleted .

Interesting little scripps video simulating how icebergs melt

https://www.youtube.com/watch?v=8YC779XMvgk&feature=youtu.be
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on July 23, 2020, 08:39:03 PM
     The only way for Volume loss trend to decline relative to Extent is for Thickness to increase.  With the net energy balance of the Arctic system already above equilibrium to maintain the current seasonal ice levels, compounded by increasing energy inputs from GHG emissions that not only continue to load the system, but still doing so at any increasing rate, I see virtually no chance for Thickness levels to increase, or for the Volume rate of decline to lessen.

Not at all.  We are talking about a trend line, not an absolute value.  The volume trend line has already lessened over the past several years.

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
Title: Re: Basic questions and discussions about melting physics
Post by: sedziobs on July 23, 2020, 10:00:39 PM
Question about draining of melt ponds.

Floating ice is 9/10 under water. If a melt pond was deep enough to make a hole in the bottom of the flo the pond wouldn't drain any further than until the surface of the pond was at sea level. So 9/10 of it would remain. Are melt ponds shallow ponds whose bottom is above sea level that drain from the side? I find that hard to believe since the extra heat from the sun should warm the water uniformly and the only ice to melt in the center of the pond would be at the bottom.

My understanding is that melt ponds form when fresh meltwater enters the pores of an ice floe and then freezes within it, thereby making it non-porous. The bottom of the pond can then deepen to below sea level without draining. The volume of the pond grows from the bottom as the ice melts. Eventually enough heat is added that the fresh meltwater drains through the ice, and sits just below the ice but above the salty seawater.

Below is Jim Hunt's chart of the temperature profile for a buoy (the x-axis is vertical position from the top in 2cm increments).
 
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=327.0;attach=276082;image)

My interpretation: the purple line shows conditions on June 1, as air temperatures are above 2C and surface melt is starting. Temperatures abruptly drop beginning 1m from the top sensor (position 50) to -3.5 C in the center of the ice, and then slowly rise to the -1.8C temperature of the seawater about 3m from the top sensor (2m ice/snow thickness).

By June 18, the navy line shows that despite cooler air temps, the ice/snow surface has dropped about 30cm with a shallow 10cm or so melt pond at 0C sitting on top, and the ice core has warmed to the same temperature as the seawater. Fresh melt water (possibly a drained melt pond) is indicated by the temperature spike at 2.7m from the top, so the ice is now about 1.5m thick.

On June 27, air temperatures have risen again, and a 30cm deep melt pond with 0.5C water sits on the ice surface which has dropped another 30cm. The 0C meltwater under the ice has been mixed away. 

On July 1, conditions are relatively similar but air temps have spiked to 5C and 0C fresh meltwater is sitting at 2.5m. The ice is now about 1m thick.

On July 15, there is a 60cm deep melt pond sitting on the surface of ice that is just over 0.5m thick.

By July 18, the bouy is no longer lodged in the ice and has dropped about 50cm. A 40cm deep melt pond at 1.5C sits on top of the ice, and a pool of water that is warmer than the seawater but below 0C sits under the ice. That may indicate that the meltpond is slowly draining and mixing with the seawater.   

My interpretation of the buoy charts may be flawed in some ways, but I think the general process is meltponds form, possibly warm to above 0C, and drain to below the ice but above the seawater. 

More information can be found in the buoys thread (https://forum.arctic-sea-ice.net/index.php/topic,327.1900.html)
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on July 23, 2020, 10:11:52 PM
Not at all.  We are talking about a trend line, not an absolute value.  The volume trend line has already lessened over the past several years.
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
    I see nothing in the link to PIOMAS update about the trend line slope for Volume becoming less negative.  What it does say is "Sea ice volume is an important climate indicator. It depends on both ice thickness and extent."  In order for Volume trend to change, antecedent values in Thickness and/or Extent must change in the same direction.

    I don't understand the relevance of your distinction between trend and absolute value.

    You are free to consider the Extent linear trend estimate (2072) instead of the Volume linear trend estimate (2032) as the better estimator for when September ASI for both measures will approach zero  (see https://forum.arctic-sea-ice.net/index.php/topic,2348.msg273488.html#msg273488 (https://forum.arctic-sea-ice.net/index.php/topic,2348.msg273488.html#msg273488)).  But you won't have much company in thinking that.
 
     As much as I can guarantee anything, I guarantee you that the date for Extent going below 1M km2 is better predicted by the Volume trend line on Wipneus chart as 2030 =+/- 6 years,
(https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd7.png?attachauth=ANoY7cqAUQcI0rwnHAQAzT_E9QNRrPfclk16ukajLq807f1rbnia0T46ZodfJCSV84_Xvzza7fxr4xVrHWsNjDP_YX9mAhFv-AhJkivEDT9wSJnsVJuVKH_gECZVA_xBmV7pvfwjMquCSxUftJ6w4T7KI51hpoo_auysuvdpkWG2-4svLOsROtn5S3tPWDYSqjWmHz-OviARufq16Dfs7oDONgBxGmm0-9cWiCAr9OyOEGoBaqR8FbDAhjsp3v6AsiSQoQQ429Kz&attredirects=0]https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd7.png?attachauth=ANoY7cqAUQcI0rwnHAQAzT_E9QNRrPfclk16ukajLq807f1rbnia0T46ZodfJCSV84_Xvzza7fxr4xVrHWsNjDP_YX9mAhFv-AhJkivEDT9wSJnsVJuVKH_gECZVA_xBmV7pvfwjMquCSxUftJ6w4T7KI51hpoo_auysuvdpkWG2-4svLOsROtn5S3tPWDYSqjWmHz-OviARufq16Dfs7oDONgBxGmm0-9cWiCAr9OyOEGoBaqR8FbDAhjsp3v6AsiSQoQQ429Kz&attredirects=0)
Title: Re: Basic questions and discussions about melting physics
Post by: mdoliner on July 23, 2020, 11:22:23 PM
sedziobs

But why would it drain if the bottom is below sea level? Even if there is different density between the water in the pond and the water in the surrounding ocean, there would still be water left in the pond.
Title: Re: Basic questions and discussions about melting physics
Post by: sedziobs on July 23, 2020, 11:58:36 PM
sedziobs

But why would it drain if the bottom is below sea level? Even if there is different density between the water in the pond and the water in the surrounding ocean, there would still be water left in the pond.

Right, I don't think there will be a dry ice surface below sea level or freeboard. Below that level, the water doesn't necessarily "drain," but rather mixes with brine. Also consider that as the water above the freeboard drains, the floe will lose mass and therefore the melt pond bottom will rise relative to freeboard. From a 2D perspective, the coverage area of a melt pond on a mostly flat but irregular ice floe can be significantly reduced when its surface elevation drops to the freeboard.

This is just what I have learned reading the forum over the years. I'm no expert by any means.
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on July 24, 2020, 02:24:43 AM
     Summary of the Thin ice accleration hypothesis -- Absent some qualitative effect that makes thinner ice HARDER to melt (which does not seem to be the case at all), even without any effect of qualitative differences for thinner ice that reduce melt resistance, it seems irrefutable that 1M km2 of 1-meter thick ice (thus 1M CUBIC meters of ice) will melt out faster than 1M km2 of 2-meter thick ice (2M cubic meters) simply because there is only half as much ice to melt. 

    As Thickness declines and approaches 1 meter in late summer (and as average albedo declines with Extent losses) the rate of Extent losses will likely increase between now and 2030.  I don't even want to be right about this, because it is kind of sickening to think about the consequences.  But my rational mind also wanted an explanation for how the Extent and Volume trends will, as they arithmetically must, meet by the time September ice approaches extinction.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on July 24, 2020, 06:09:44 AM
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 
Overreach indeed, you should never say never (or "everyone agrees" because there is always someone ...)

However, I do not think it is plausible that volume will slow down to match extent. What we are specifically talking about here is the volume and extent at minimum. Volume has been dropping much faster than extent, and at some point the two must meet (at the latest, when the ice disappers completely). A faster decrease in extent is much more likely than a slower decrease in volume at minimum. The latter would require that thinner ice somehow melts slower than thicker, or is more resilient against the other forces bent towards melt, not really very plausible.

Quote
Also, the physics is reversible.  If the ice were to thicken, it would return to its previous state.
That is not what is meant by reversible physics. I was specifically referring to Glen's idea of the rate of melt at different thickness being similar to the rate of freeze at different thickness. But generally speaking, real world physics are not reversible ever (because of quantum as Terry would say).
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on July 24, 2020, 02:47:22 PM
Not at all.  We are talking about a trend line, not an absolute value.  The volume trend line has already lessened over the past several years.
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
    I see nothing in the link to PIOMAS update about the trend line slope for Volume becoming less negative.  What it does say is "Sea ice volume is an important climate indicator. It depends on both ice thickness and extent."  In order for Volume trend to change, antecedent values in Thickness and/or Extent must change in the same direction.

    I don't understand the relevance of your distinction between trend and absolute value.

    You are free to consider the Extent linear trend estimate (2072) instead of the Volume linear trend estimate (2032) as the better estimator for when September ASI for both measures will approach zero  (see https://forum.arctic-sea-ice.net/index.php/topic,2348.msg273488.html#msg273488 (https://forum.arctic-sea-ice.net/index.php/topic,2348.msg273488.html#msg273488)).  But you won't have much company in thinking that.
 
     As much as I can guarantee anything, I guarantee you that the date for Extent going below 1M km2 is better predicted by the Volume trend line on Wipneus chart as 2030 =+/- 6 years, (see https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd7.png?attachauth=ANoY7cqAUQcI0rwnHAQAzT_E9QNRrPfclk16ukajLq807f1rbnia0T46ZodfJCSV84_Xvzza7fxr4xVrHWsNjDP_YX9mAhFv-AhJkivEDT9wSJnsVJuVKH_gECZVA_xBmV7pvfwjMquCSxUftJ6w4T7KI51hpoo_auysuvdpkWG2-4svLOsROtn5S3tPWDYSqjWmHz-OviARufq16Dfs7oDONgBxGmm0-9cWiCAr9OyOEGoBaqR8FbDAhjsp3v6AsiSQoQQ429Kz&attredirects=0 (https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd7.png?attachauth=ANoY7cqAUQcI0rwnHAQAzT_E9QNRrPfclk16ukajLq807f1rbnia0T46ZodfJCSV84_Xvzza7fxr4xVrHWsNjDP_YX9mAhFv-AhJkivEDT9wSJnsVJuVKH_gECZVA_xBmV7pvfwjMquCSxUftJ6w4T7KI51hpoo_auysuvdpkWG2-4svLOsROtn5S3tPWDYSqjWmHz-OviARufq16Dfs7oDONgBxGmm0-9cWiCAr9OyOEGoBaqR8FbDAhjsp3v6AsiSQoQQ429Kz&attredirects=0))
   
 

It was the change in slope of the volume anomaly in Fig. 1.  Perhaps this post by Stephan would help, stating that the long term trend for volume increased by one year, while the long term trend for extent decreased by two years.  I do not see how volume is a predictor for extent any more than extent is a predictor for volume.  They must converge, but likely somewhere in the middle.  Perhaps in 2052 as indicated by the thickness extrapolation.

https://forum.arctic-sea-ice.net/index.php/topic,2348.msg276462.html#msg276462
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on July 24, 2020, 03:23:32 PM
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 
Overreach indeed, you should never say never (or "everyone agrees" because there is always someone ...)

However, I do not think it is plausible that volume will slow down to match extent. What we are specifically talking about here is the volume and extent at minimum. Volume has been dropping much faster than extent, and at some point the two must meet (at the latest, when the ice disappers completely). A faster decrease in extent is much more likely than a slower decrease in volume at minimum. The latter would require that thinner ice somehow melts slower than thicker, or is more resilient against the other forces bent towards melt, not really very plausible.

Quote
Also, the physics is reversible.  If the ice were to thicken, it would return to its previous state.
That is not what is meant by reversible physics. I was specifically referring to Glen's idea of the rate of melt at different thickness being similar to the rate of freeze at different thickness. But generally speaking, real world physics are not reversible ever (because of quantum as Terry would say).

I think it is less of either/or than both converging together.  In that case, extent would decrease faster, while volume decreases slower, merging when the ice disappears.  Note that thickness is decreasing at a rate in between volume and extent (roughly halfway according to Stephan's table).  Mathematically, this ensures that volume would decrease faster (initially) than extent as the added dimension (thickness) is decreasing also.  If thickness were held constant, volume and extent would decrease at the same rate.  As I pointed out to Glen, the slope of the volume decrease has lessened over the past decade, indicating that volume is decreasing at a slower rate.

It is not a matter of thinner ice melting at a different rate, which it does (we agree on that point).  Rather it is the location of the ice (further poleward) that matters more greatly.  The angle of the sun means that less incoming solar radiation is available for melt.  Granted, this point can be argued, and has been to a great deal. 
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on July 25, 2020, 08:05:55 AM
I think it is less of either/or than both converging together.  In that case, extent would decrease faster, while volume decreases slower, merging when the ice disappears.  Note that thickness is decreasing at a rate in between volume and extent (roughly halfway according to Stephan's table).  Mathematically, this ensures that volume would decrease faster (initially) than extent as the added dimension (thickness) is decreasing also.  If thickness were held constant, volume and extent would decrease at the same rate.  As I pointed out to Glen, the slope of the volume decrease has lessened over the past decade, indicating that volume is decreasing at a slower rate.

Be careful not to fall into the circular argument trap. Average thickness is calculated from volume vs. extent and changes in a derived value tell us nothing extra.

Besides, the mathematics of the case are not important. This is a physical system, highly complex and variable. And I disagree that there is any indication of the slope of the volume decrease slowing down over the last decade. The variability is too great to allow any such conclusion. The image below, from Stephen's post (https://forum.arctic-sea-ice.net/index.php/topic,2348.msg276763.html#msg276763) gives me absolutely no indication of a slowdown.

Quote
It is not a matter of thinner ice melting at a different rate, which it does (we agree on that point).  Rather it is the location of the ice (further poleward) that matters more greatly.  The angle of the sun means that less incoming solar radiation is available for melt.  Granted, this point can be argued, and has been to a great deal.

This is an extremely simplified view of the physics of the system. I have argued for the opposite effect, i.e. the smaller the polar ice cap, the easier it is to melt because of the amount of open water surrounding it.

I'll perhaps expound on that further in another post, but here is the graph I promised. Just from eyeballing the graph and doing some quick calculations, the annual volume loss ticks in at 300 km3 over a 45 year period (1975-2020).

The apparent "slowdown" that you think you see in the last decade is not statistically valid - but the large fluctuation is interesting, and could perhaps be indicative of a stalled acceleration. In other words, the system could be trying to accelerate melt after 2010 but a temporary stall in the middle of the decade confuses the picture.
Title: Re: Basic questions and discussions about melting physics
Post by: wdmn on August 12, 2020, 06:07:20 PM
I'm trying to conceptualize a seemingly simple problem about freezing physics. My goal is to determine air temperatures at which ice forms rapidly on the surface (assuming no waves/little wind). After some thought I have decided I have to first think in terms of melting physics.

If we have the enthalpy of fusion for ice at:

333.55 J/g (heat of fusion of ice) = 333.55 kJ/kg = 333.55 kJ for 1 kg of ice to melt

If we want to simplify this and understand melting potential just from the watts/m2 from insolation + air temperature (assuming the latter is possible), we could calculate roughly 1 kg of ice into m2 (for a given thickness). This then becomes a question of thermal conductivity between air/insolation in W/m2 and ice in m2.

In order to think about freezing, I reverse and further simplifying this problem, by first eliminating insolation as a factor (ice often forms at night in lower latitudes and in the arctic insolation is not a factor for most of freezing season), and just getting a watts/m2 value from water at 4, 3, 2 and 1 degree celsius (how, I don't know), and imagining this as an energy source trying to heat the surrounding air, and then calculating at what air temperature ice rapidly forms due to the heat source in the water no longer being able to keep air temperature at the surface of the water above freezing.

I'm wondering if I am even approaching it right in wanting to think about W/m2 between two surfaces (the surface of the water, and the surface of the adjacent air, where both temperatures could be known), treating it as the water heating the air, rather than the air cooling the water. Obviously it would be better to have a W/m3 measure, but maybe m2 is simpler for now...

Any general advice to sort out my thinking would be much appreciated.
Title: Re: Basic questions and discussions about melting physics
Post by: blumenkraft on August 12, 2020, 06:11:15 PM
Wdmn, the phase change itself needs energy.

Have you considered this?

Link >> http://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/thermo/phase.html

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fhydrogen.physik.uni-wuppertal.de%2Fhyperphysics%2Fhyperphysics%2Fhbase%2Fthermo%2Fimgheat%2Fpha1.gif&hash=f87098b5bbc0399aff5547c579a6d1e3)
Title: Re: Basic questions and discussions about melting physics
Post by: wdmn on August 12, 2020, 06:14:18 PM
Thanks Blumenkraft,

I have seen that graph. I'm just wondering how to start thinking about kJ/kg in terms of temperature that is not instantaneous (I assume all of those kJ need not be available at the same instant in order for melt to occur, since it occurs over time)...
Title: Re: Basic questions and discussions about melting physics
Post by: Tor Bejnar on August 12, 2020, 07:55:08 PM
The 'rule of thumb' is that Arctic sea water generally starts actually freezing when the air temperature gets down to -10C.  The reasoning behind this, I recall (I'm not a physicist) is that sea water cooled at the surface sinks and is replaced by the warmer water from just below.  Actual freezing starts when the rate of heat exchange at the surface overtakes the rate of vertical water circulation.

In very calm seas (e.g., protected bays), the -10C rule doesn't apply: sea water freezes under less-cold air temperatures.  I presume a pre-chilled water column and less salty water also freeze more easily under less-than-extreme cold air.  Strong winds will speed up vertical water circulation.

But I cannot help with the equations to express this!
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on August 19, 2020, 08:07:28 PM
From https://nsidc.org/arcticseaicenews/2020/8/ (https://nsidc.org/arcticseaicenews/2020/8/)
  NSIDC update August 18 2020

     "Note how the projections have seesawed up and down from June through mid-August. This is a result of the changes in the extent loss rates from one period to the next; it highlights how strongly weather conditions affect the ice loss through the summer, as well as the influence of thickness on how fast ice is melted away."   (emphasis added)

      I suspect that relationship will be a key factor resulting in accelerated melt rates in coming years.  It would be very interesting to see a chart that helps quantify the influence of thickness on ice melt rate.  Surely such a chart must exist somewhere, but I have not seen it.  If anyone has an image or link please post it.  Thanks in advance for anyone who can do so.
Title: Re: Basic questions and discussions about melting physics
Post by: interstitial on August 19, 2020, 09:16:01 PM
The 'rule of thumb' is that Arctic sea water generally starts actually freezing when the air temperature gets down to -10C.  The reasoning behind this, I recall (I'm not a physicist) is that sea water cooled at the surface sinks and is replaced by the warmer water from just below.  Actual freezing starts when the rate of heat exchange at the surface overtakes the rate of vertical water circulation.

In very calm seas (e.g., protected bays), the -10C rule doesn't apply: sea water freezes under less-cold air temperatures.  I presume a pre-chilled water column and less salty water also freeze more easily under less-than-extreme cold air.  Strong winds will speed up vertical water circulation.

But I cannot help with the equations to express this!
After an extended discussion in one of the previous melt years I think the consensus was this rule of thumb was true for a specific region. If a region still has ice at the start of the melt season it can freeze at higher temperatures.
Title: Re: Basic questions and discussions about melting physics
Post by: johnm33 on August 19, 2020, 10:10:45 PM
The rule of thumb came from http://eh2r.blogspot.com/2016/10/new-sea-ice-starts-from-3-important.html
The strangeness of the physics of water continues to surprise me.
Title: Re: Basic questions and discussions about melting physics
Post by: interstitial on August 19, 2020, 10:22:47 PM
The rule of thumb came from http://eh2r.blogspot.com/2016/10/new-sea-ice-starts-from-3-important.html
The strangeness of the physics of water continues to surprise me.
I am not sure who the blogger is so no way to asses them. Perhaps you are correct. IDK
I am amazed they are still making discoveries about water.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 20, 2020, 07:00:38 AM
The 'rule of thumb' is that Arctic sea water generally starts actually freezing when the air temperature gets down to -10C.  The reasoning behind this, I recall (I'm not a physicist) is that sea water cooled at the surface sinks and is replaced by the warmer water from just below.  Actual freezing starts when the rate of heat exchange at the surface overtakes the rate of vertical water circulation.

In very calm seas (e.g., protected bays), the -10C rule doesn't apply: sea water freezes under less-cold air temperatures.  I presume a pre-chilled water column and less salty water also freeze more easily under less-than-extreme cold air.  Strong winds will speed up vertical water circulation.

But I cannot help with the equations to express this!
After an extended discussion in one of the previous melt years I think the consensus was this rule of thumb was true for a specific region. If a region still has ice at the start of the melt season it can freeze at higher temperatures.
I think that was the agreement, yes. New ice would grow out from existing ice much sooner than open water would start freezing.
Title: Re: Basic questions and discussions about melting physics
Post by: Phil. on August 22, 2020, 03:30:06 PM
The rule of thumb came from http://eh2r.blogspot.com/2016/10/new-sea-ice-starts-from-3-important.html
The strangeness of the physics of water continues to surprise me.
I am not sure who the blogger is so no way to asses them. Perhaps you are correct. IDK
I am amazed they are still making discoveries about water.

That's Wayne, he makes measurements in the CAA so has personal knowledge of the ice formation there.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 22, 2020, 04:12:51 PM
Following some discussion on albedo of ice, water and meltponds, I've decided to post these musings here rather than in the Mosaic forum:

The whole albedo thing has me confused. Albedo basically means "whiteness" and is a measure of diffuse reflection of solar radiation from the surface. So a white surface reflects lots, a black surface reflects very little.

Absolutely pure water is essentially transparent to light, and the same goes for pure ice, since visible light does not react to H2O molecules. But the angle of the incoming light plays a role here as well, the lower the angle of incident, the higher the amount of reflection and I'm guessin that if the angle of incident is lower than the angle of refraction, all the light will be reflected.

In the real world, ice has an uneven surface and lots of air bubbles, so almost all of the incoming radiation will quickly find an air/ice interface with a lesser angle of incident than the refracting angle, and bounce off. Hence the white appearance of ice, and the fact that the whiteness diminishes with fewer air pockets and bigger crystals (something a lot of us have experienced directly).

Real-world water is still mostly transparent to light, and if the water is pure enough or shallow enough, the light is reflected by the bottom (as is the case with the melt ponds).

But albedo says nothing about whether the material absorbs energy from the incoming radiation. And as A-Team pointed out, neither water molecules nor salt ions absorb energy from visible light.

Which basically means that the only way the sun can melt ice or warm water is by being absorbed by impurites in the ice or the water. And since water is so much more transparent, the incoming light has a much bigger change of hitting impurities in water than in ice given same level of purity. In the oceans, the amount of impurities is such that sunlight rarely reaches more than a few meters before being absorbed.
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on August 22, 2020, 04:51:19 PM
Binntho,
You are correct in that water absorbs almost all incoming solar radiation (~94%).  However, ice reflects between 50 and 70% of incoming radiation, with the remainder being absorbed.  Snow is even higher, >90% reflected.  Air bubbles have little effect on albedo.  Contrary to what A-team claims, water does absorb energy, otherwise there would be no heat gradients in the seas.  The angle of radiation is an indication of the intensity of the incoming radiation,
Title: Re: Basic questions and discussions about melting physics
Post by: interstitial on August 22, 2020, 06:32:44 PM
The entire light spectrum includes ultraviolet, visible and infrared. The simple answer is seawater is opaque in UV and IR. The mid-level answer for visible is shown in the following table.
   
 Loss of light (percent) in one metre of seawater*
       

violet   blue-green  yellow   orange   red
*According to Jerlov.
wavelength (micrometre)

   0.30   0.400.46   0.50   0.54   0.58   0.64   0.70
     oceanic water, most transparent   
16%   4%   2%   3%   5%   9%   29%   42%   
    oceanic water, least transparent   
57%   16%   11%   10%   13%   19%   36%   55%     
coastal water, average   
63%   37%   29%   28%   30%   45%   74%   https://www.britannica.com/science/seawater/Optical-properties (https://www.britannica.com/science/seawater/Optical-properties)The PHD level answer is in the following paper.https://www.osapublishing.org/DirectPDFAccess/E5ACAF41-E42F-0EF7-70D5D62785190BF5_301984/oe-22-21-25093.pdf?da=1&id=301984&seq=0&mobile=no (https://www.osapublishing.org/DirectPDFAccess/E5ACAF41-E42F-0EF7-70D5D62785190BF5_301984/oe-22-21-25093.pdf?da=1&id=301984&seq=0&mobile=no) 


 


























 
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 23, 2020, 05:42:20 AM
Binntho,
You are correct in that water absorbs almost all incoming solar radiation (~94%).  However, ice reflects between 50 and 70% of incoming radiation, with the remainder being absorbed.  Snow is even higher, >90% reflected.  Air bubbles have little effect on albedo.  Contrary to what A-team claims, water does absorb energy, otherwise there would be no heat gradients in the seas.  The angle of radiation is an indication of the intensity of the incoming radiation,
This sounds llke you are assuming that albedo and absorbtion are the same thing, and I note that A-team seems to confusing the two also over on the Mosaic thread )on second reading I see no confusion). What I'm saying is that they are not - although they will normally follow each other. But to take an example, window glass has a very low albedo and yet abosrbs very little energy.

And the obvious reason for why the oceans absorb solar energy in the well-known heat gradient is that the ocean is full of impuirities that block the solar light and absorb the heat. These impurities begin with the diatom and the foraminifera that populate the top centimeters of ocean, precisely because they are trying to catch the incoming sunlight!

And when you think about it, this is exactly what the whole thing is about - diatoms produce up to half the planetary oxygen and constitute a signifcant proportion of it's biomass. And all through catching sunlight in the top layers of ocean.

And how can you claim that air bubbles have little effect on albedo? Have you ever seen clear glacier ice, ice that has been compressd under hundreds of meters for thousands of years? I have, and I can tell you that it is transparent as window glass. And in still weather, newly formed lake ice is transparent as window glass. What makes snow and normal ice white to the eye is precisely the number of ice - to -air interfaces, both on the surface of snow flakes and wherever there is trapped air in ice.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 23, 2020, 05:43:59 AM
The entire light spectrum includes ultraviolet, visible and infrared. The simple answer is seawater is opaque in UV and IR. The mid-level answer for visible is shown in the following table.
The ultraviolet and infrared portions are very small. Window glass blocks UV light, and yet there is no discernible drop in incoming radiation.

So no this is not an explanation.
Title: Re: Basic questions and discussions about melting physics
Post by: The Walrus on August 23, 2020, 02:39:34 PM

And how can you claim that air bubbles have little effect on albedo? Have you ever seen clear glacier ice, ice that has been compressd under hundreds of meters for thousands of years? I have, and I can tell you that it is transparent as window glass. And in still weather, newly formed lake ice is transparent as window glass. What makes snow and normal ice white to the eye is precisely the number of ice - to -air interfaces, both on the surface of snow flakes and wherever there is trapped air in ice.

Yes, I have.  It is also bluish in color.  Newly formed ice is newly transparent because it is razor-thin.  As water freezes, the dissolved air becomes trapped in the ice, forced out under pressure after years of compression.  Yes, it does have a measurable effect, but it is small compared to the difference between ice and water.

To add to your comment about UV and IR, the incoming heat radiation is mainly from the IR portion of the spectrum.  When discussing energy used to heat the water or ice, that is the important region.  UV is largely irrelevant.  The longer wavelengths of the visible spectrum contribute just like the near IR.

No, albedo and absorption are not the same.  However, albedo greatly influences the amount of energy absorbed.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 23, 2020, 03:35:00 PM

And how can you claim that air bubbles have little effect on albedo? Have you ever seen clear glacier ice, ice that has been compressd under hundreds of meters for thousands of years? I have, and I can tell you that it is transparent as window glass. And in still weather, newly formed lake ice is transparent as window glass. What makes snow and normal ice white to the eye is precisely the number of ice - to -air interfaces, both on the surface of snow flakes and wherever there is trapped air in ice.
Yes, I have.  It is also bluish in color.  Newly formed ice is newly transparent because it is razor-thin. 

Water and ice is bluish because of what A-Team said about quantum. And new ice is not transparent because it is razor thin. I have walked on ice as transparent as windowglass. Compressed glacier ice is also as transparent as window glass. So thickness has nothing to do with it, while the absence of trapped air pockets is the obvious explanation.

Both water and ice are made of H2O and this molecule is near-transparent to visible light. And both water and ice is near transparent when absolutely pure, and in the case of ice, without airpockets.

So it is obvious that it is the air pocktets in ice that cause it's high albedo. Or how else wil you explain it?

Quote
As water freezes, the dissolved air becomes trapped in the ice, forced out under pressure after years of compression.  Yes, it does have a measurable effect, but it is small compared to the difference between ice and water.

What difference between air and water are you referring to, what is this "difference" that makes the obvious effects of air pockets totally insignificant? If air pockets are not the explanation for the high albedo of ice, please supply another explanation!

Quote
To add to your comment about UV and IR, the incoming heat radiation is mainly from the IR portion of the spectrum. 

Well, not really. It's closer to 50/50 at the surface. But it is still more than I expected, I thought the majority of incoming energy at the surface was in the visible spectrum.

Which essentially answers my original question to A-Team. The solar energy that hits the surface is only half visible light, the other half is infrared. Albedo only applies to visible light, while energy absorbtion applies to all wavelengths.

So a totally pure water column will be transparent to visible light while still absorbing the infrared part of the spectrum. But any impurities in the water will absorb the visible light, and ocean water is far from being free of impurities.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 24, 2020, 07:24:04 AM
My contention is that when it comes to water and ice, albedo is directly linked to the number and variability of water/air or ice/air interfaces. Clear and pure water / ice, with one smooth interfce with air. will be transparent with very low albedo, but once you have air bubbles / air pockets / fractal surface then albedo shoots up.

With ice, this is very easily demonstrable. Pure ice without any air bubbles is transparent with very low albedo. Normal ice, with lots of air pockets and bubbles, and a rough surface, is practically opaque with a high albedo, while fresh snow, with an almost fractal surface to air interface, is pure white with close to 100% albedo.

(The higher albedo of ice covered with water rather than air is linked to the difference in refraction between the two interfaces. My hypothesis is that if the angle of incident is lower than the angle of refraction, then all light is reflected. The higher the angle of refraction, the more likely it is that the angle of incident is lower in any given part of a rought surface - which reminds me that even when covered with water, transparent ice becomes no less transparent).

As for water, anybody can turn on the faucet and observe how a smooth flow is transparent, but once the water breaks up into droplets it quickly becomes opaque and tends towards white.

But yesterday I remembered an observation I made last month but didn't tie in with the albedo discussion until now. Having lived for a couple of years in central Europe, I'd noticed that during a good thunderstorm, visibility would fall to a few tens of meters. In fact, I used the visibillity factor to gauge the intensitity of thunder storms: The most intense would make the houses on the other side of the yard invisible.

But here in the Tropics, thunderstorms that seem to be delivering quite a lot more water than the Europan ones, still have much less effect on visibility. And the difference became apparent when I thought about it: Tropical thunderstorms have much bigger raindrops than the European ones. And bigger raindrops with same amount of rain lowers the number of air/water interfaces, hence lowers albedo and increases visibility.

So my conviction that albedo in ice and water is all about air pockets and bubbles, or rather, number and variability of air/water and air/ice interfaces, is even stronger than before. But I've not idea if it is the correct, or scientifically accepted, explanation.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on August 24, 2020, 09:26:11 AM
Maybe it would be better to read some scientific literature about it?
Title: Re: Basic questions and discussions about melting physics
Post by: P-maker on August 24, 2020, 12:32:11 PM
Binntho,

I do agree with your general observations that - large glacier ice crystals, large and slowly formed lake ice crystals and large Tropical raindrops from great altitudes - are basically transparent.

However, small ice crystals in snow, tiny air bubbles in lake ice and droplets in typical drizzle gives a whiter impression.

Thus, size matters!

Comparing a clear blue sky over Iceland with a "clear" sky over Italy gives you a clear impression of the difference between a blue sky and a white sky.

The latter is full of moisture, impurities and what have you. The former is totally devoid of impurities.

Thus, maybe the content of the bubbles in the ice may be of importance. It is not just the physical aspects af refraction/ reflection that matters, but also the content of the air in bubbles trapped in the ice which makes a difference?
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 24, 2020, 02:06:43 PM
Maybe it would be better to read some scientific literature about it?

Why on earth would you say that? I see all sorts of people making all sorts of claims off the top of their hats without having the faintest clue about what they are saying, and that's fine by you, the less science the better at times it seems.

I then make a fairly good case for my view, with evidence and reasoning and try to avoid presumptions and wild unsubstantiated claims, hoping to start a balanced and evidence-driven discussion.

But instead of taking part, or keeping quiet, you feel driven to make a comment like this? Perhaps you are suggesting that we all stop posting on subjects in which we do not have degrees, or without extensive footnotes and references to scientific publications?

It is the opinion of this said poster that condescension is all too common in this forum. Please try to avoid it.
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on August 24, 2020, 02:10:25 PM
Thus, size matters!
What about quality?  ;D

Comparing skies over Iceland and Italy has no bearing on what I am saying.

Quote
It is not just the physical aspects af refraction/ reflection that matters, but also the content of the air in bubbles trapped in the ice which makes a difference?

Not really. The only thing that matter in my opinion is the number and variation of interfaces between transparent mediums (air, water and ice). I've thought about this, it seems obvous, and nobody is putting forth any evidedence to the contrary.
Title: Re: Basic questions and discussions about melting physics
Post by: oren on August 24, 2020, 04:16:55 PM
I did not mean to condescend, but this is a well researched subject. Trying to figure out albedo and absorption of melt ponds from first physics principles and intuition could lead one astray. Best to consult the scientific literature. which I would myself if I had the time.
Title: Re: Basic questions and discussions about melting physics
Post by: Tor Bejnar on August 24, 2020, 04:38:45 PM
What Causes Ice to Turn White?  (https://generalparts.com/help-my-ice-is-white/)
I don't know the source, but it was at the top of my internet search ...
Quote
Ice appears white when it contains trapped air bubbles and minerals. Some of the more common impurities found in water are minerals like calcium and magnesium, as well as sediment. As these things freeze, gases are released, creating air bubbles and causing ice to shrink on occasion. If you have noticed that your ice maker appears to be producing ice of a smaller size, this is likely the issue.

2nd internet link:  I've heard of these folks ...
Why Ice Usually Freezes Cloudy, Not Clear (https://science.howstuffworks.com/nature/climate-weather/atmospheric/why-ice-usually-freezes-cloudy-and-not-clear.htm)
Quote
...
 along with suspended sediments, dust particles or flecks of minerals like calcium and lime. It may also harbor lots of dissolved gases, such as oxygen. (Without said oxygen, fish wouldn't be able to breathe.) Gases and physical impurities are the key to understanding why those ice cubes in your lemonade pitcher are so darn cloudy.
Title: Re: Basic questions and discussions about melting physics
Post by: Bruce Steele on August 24, 2020, 04:59:26 PM
https://www.frontiersin.org/articles/10.3389/fmars.2020.00183/full
From post #621 “Arctic Ocean Salinity temp and waves”

So melt ponds do allow more light and heat through the ice than the white ice that results from melt ponds draining. Documented.

From other reading I can’t immediately source. When saltwater freezes the salt remaining in the ice forms little tubes as it drains down through the ice. Those little tubes allow bubbles to form when melt ponds drain and the water inside the tubes is allowed to drain out . So the ice becomes “white ice” after melt ponds drain and albedo increases.

Not the same article I was talking about but shows tubes in the ice and says they result in bubbles inside the ice.

https://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html
Title: Re: Basic questions and discussions about melting physics
Post by: wdmn on August 31, 2020, 05:52:13 PM
This may have been posted before, but thought it would be of interest (in spite of its age).

The image compares multiple records of ice break in rivers, bays and lakes, and plots them in terms of rate of melt based on ice thickness (y axis) and duration of melt (in days; x axis). It then plots hypothesied minimum and maximum melt rates, where the maximum rate has lots of movement in the water (wind, waves, currents), and the minimum is based solely on increasing air temperatures.

The image comes from the paper:

CORRELATING FREEZE-UP AND BREAK-UP WITH WEATHER CONDITIONS by G. P. Williams, 1965.

https://www.nrcresearchpress.com/doi/pdfplus/10.1139/t65-047
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on October 06, 2020, 02:51:01 AM
  From the "When will the Arctic Go Ice Free?" thread.  But my reply is more about ice physics so put it here.
Not sure that thinking about volume as being decreased is the right approach. 

To first order, so ignoring pesky complicating factors like winds and currents moving ice around, isn't maximum ice area a measure of how much space gets cold enough, and maximum ice thickness a measure of the amount of heat loss in that area? The slow decline in area says that it still gets cold enough to create ice in much the same area, but the relatively rapid decline in ice thickness says that nonetheless there is a lot more heat in the system so less ice can be made. Both are likely to keep heading as they are and volume just is the result of combining the two.

     I agree that Volume is a function of Area and Thickness, so your logic makes sense to me.  But what I think gerontocrat was getting at was that as the ice thins, qualitative changes occur to increase the melt rate for the same degree of melting energy.

     I also began promoting that argument last year.  While I still think it is true, I have to partially recant my previous contention that once Arctic sea ice gets below 2 meters the melt rate should increase rapidly due qualitative changes in the ice.  The door shut on that when I read Maycut and Rothrock 2004: "While summer melting of undeformed ice is nearly independent of thickness, winter ice growth rates depend inversely on thickness." 
     Changes in the thickness distribution of Arctic sea ice between 1958–1970 and 1993–1997
     Y. Yu  G. A. Maykut  D. A. Rothrock. 2004
https://doi-org.wv-o-ursus-proxy02.ursus.maine.edu/10.1029/2003JC00198 (https://doi-org.wv-o-ursus-proxy02.ursus.maine.edu/10.1029/2003JC00198)

     The winter ice growth part of that conclusion is demonstrated in the first chart below from
Thorndike, A. S., D. A. Rothrock, G. A. Maykut, and R. Colony.  1975.  The thickness distribution of sea ice. J. Geophys. Res., 80, 4501–4513.  Abstract at:  https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JC080i033p04501 (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JC080i033p04501).  (Good luck finding the PDF.  I gave up.  You'd think that a seminal paper like that would be easy to find.)

     Zhang and Rothrock 2001 provide some data on the effect of ASI thickness on summer melt rate.  That rate increase is much smaller than I had expected.  It does not have an appreciable impact until thickness is below 1 meter, and even at 0.5 meter the rate is only about 25% faster than the rate for 2 meter thick ice.
     Jinlun Zhang and Drew Rothrock.  2001. A Thickness and Enthalpy Distribution Sea-Ice Model.  J. Phys. Oceanogr. 31 (10): 2986–3001.
https://doi.org/10.1175/1520-0485(2001)031<2986:ATAEDS>2.0.CO;2 (https://doi.org/10.1175/1520-0485(2001)031<2986:ATAEDS>2.0.CO;2)

     The second chart below shows the source of the data for my derivative 3rd chart, which shows the degree of melt acceleration due to thinning ice.  Along the X axis are different average ice thicknesses (thicker on the left) from the PIOMAS data.  The melt rate is from polynomial regression of data points from the solid line in the Zhang and Rothrock chart.  The vertical axis is the estimate cm of melt per day in June-August. 

     But what really shifted my view was reading Goosse et al. 2009.  It is a wonderful article that explains a lot about ice melting behavior.  Paradoxically (to me at least) they explain why thick ice loses more from year to year than thin ice.
     Increased variability of the Arctic summer ice extent in a warmer climate
     H. Goosse  O. Arzel  C. M. Bitz  A. de Montety  M. Vancoppenolle.  2009
     https://doi.org/10.1029/2009GL040546 (https://doi.org/10.1029/2009GL040546)
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on October 06, 2020, 03:10:51 AM
....but, the plot thickens even if the ice won't.

     There is more to the situation than thickness alone.  Structural integrity, decreasing albedo etc. seem very likely to provide reinforcing feedbacks as ASI declines.  Here's a list of potential positive and negative feedbacks not accounted for in a simple regression trend extrapolation.

Acceleration factors NOT accounted for:
     Higher salinity and lower melt resistance of thinner and thus generally younger ice.
     Increased open water leads to longer wind fetch and increased wave height.
     Reduction of mechanical strength and structural integrity of thinner ice leads to fracturing of contiguous ice into smaller pieces.
     Ice fractured into small floes is more vulnerable to wind and current transport into melting zones of the lower latitude CAA and Beaufort Seas following the typical ice movement, and by export via the Fram Strait into Greenland Sea, and also into the lower latitude peripheral ESS, Laptev, Kara and Barents Seas.  As those seas progressively melt out earlier in the summer, that reduces their physical blockage against ice exports out of the CAB.
     Increased proportion of Arctic Ocean as open water results in albedo decrease and increased solar energy absorption during summer, warming surface water.
     Combination of increased wind and open water increases water column turbulence, increases Ekman pumping, weakens halocline thermal isolation, and warms surface water.
     Fractured ice has higher proportional exposure of lateral surface area to ocean water melting energy.
     Greater portion of open water in fall and winter increases atmospheric humidity and cloud cover,  thus increasing reflection of long wave energy emitted from open water back down resulting in (relatively) warmer Arctic night.
     Warmer Arctic Ocean water in summer is likely to generate more cyclone activity leading to more wind damage and Ekman pumping.
     Warmer Arctic air temperatures decrease gradient with lower latitude air, reduces jet stream strength, and thus reduces Arctic isolation from warm southerly air masses.
     Earlier seasonal melt of snow cover on land surfaces surrounding Arctic Ocean increases terrestrial warming that then warms overlying air masses that carry some of that energy into the Arctic Ocean.
     Warmer Arctic air holds more moisture potentially resulting in more rainfall onto sea ice thus increases energy transfer from atmosphere to ice.  The latent energy per gram in liquid rain is large relative to the energy required to melt a gram of ice.
     Progressively stronger Atlantification and Pacification of Arctic Ocean waters are huge influences promoting loss of Arctic seas ice.

Deceleration factors not accounted for:
     The remaining ice more likely to be located in protected bays and other locations less exposed to melting energy.
     With loss of multiyear ice, Volume losses due to Farm export has declined and may continue to decline.
     Rapid freeze and thickening of thin ice allows rate of winter ice formation to quickly recover from summer losses, thus restoring Extent and Area coverage to maintain albedo for following summer.
      Warming surface water and increased melt strengthens the gradient protecting surface fresh water lens from subsurface heat?
     Greater area of open water in fall and winter accelerates greater ocean water energy loss to atmosphere (but rapid thin ice recovery provides insulation to work against this).
     Greater area of open water in summer increases cloudiness to block incoming solar energy.
     Warmer Arctic air holds more moisture potentially resulting more snow deposition to increase albedo on ice and surrounding land masses.
Title: Re: Basic questions and discussions about melting physics
Post by: Glen Koehler on October 06, 2020, 03:22:08 AM
      Third and final chapter...
       Looking at those lists makes me wonder if it I wasn't right the first time.  (I used to tell my kids "I've never made mistake.  I thought I did one time, but it turned out later I was wrong about that.").

       Here's what I think will happen.  Some August in the next 10-12 years, that pile of heat buried just below the surface in the Beaufort Sea, and/or a similar heat bomb in the Laptev, ESS or Kara, will break through the halocline/thermocline and melt the ice so fast that even Friv won't see it coming.  That will lead to the first September BOE. 

       Subsequent years will show some rebound, but just as the system changed in 2007, the Arctic will never be the same.  A year or two or three later will be another September BOE, and from then on September BOE will be a regular thing.  And August BOE (which matters a LOT more in terms of albedo) will only be a couple of years behind September.  July BOE will take 10-15 years longer than August, but as August declines toward 1M km2, July is accumulating increasing open water exposed solar energy absorption.  There is nothing magic about 1M km2.  The earlier in the summer each km2 of reflective ice becomes dark open water means that km2 of water is exposed to more direct sunlight for a longer time, thus allowing more energy to enter the system.   
Title: Re: Basic questions and discussions about melting physics
Post by: binntho on October 06, 2020, 06:56:21 AM
Excellent summary, thanks Glen.

       Here's what I think will happen.  Some August in the next 10-12 years,

The next decade is certainly going to be interesting. Either the BOE2032 forecast that's been bouncing around for some years now is shown to have been correct (give or take a year or two) or some hitherto unknown forces will have taken over and turned all our expectations upside down  (wouldn't be the first time either).