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johnm33

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Re: Basic questions and discussions about melting and freezing physics
« Reply #200 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.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #201 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.

binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #202 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.
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Phil.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #203 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.

binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #204 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.
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Re: Basic questions and discussions about melting and freezing physics
« Reply #205 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,

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Re: Basic questions and discussions about melting and freezing physics
« Reply #206 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-propertiesThe 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 


 


























 
« Last Edit: August 22, 2020, 06:42:48 PM by interstitial »

binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #207 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.
« Last Edit: August 23, 2020, 05:50:01 AM by binntho »
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binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #208 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.
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Re: Basic questions and discussions about melting and freezing physics
« Reply #209 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.
« Last Edit: August 23, 2020, 03:00:56 PM by oren »

binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #210 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.
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binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #211 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.
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oren

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Re: Basic questions and discussions about melting and freezing physics
« Reply #212 on: August 24, 2020, 09:26:11 AM »
Maybe it would be better to read some scientific literature about it?

P-maker

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Re: Basic questions and discussions about melting and freezing physics
« Reply #213 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?

binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #214 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.
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binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #215 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.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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oren

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Re: Basic questions and discussions about melting and freezing physics
« Reply #216 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.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #217 on: August 24, 2020, 04:38:45 PM »
What Causes Ice to Turn 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
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.
Arctic ice is healthy for children and other living things because "we cannot negotiate with the melting point of ice"

Bruce Steele

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Re: Basic questions and discussions about melting and freezing physics
« Reply #218 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
« Last Edit: August 24, 2020, 05:16:11 PM by Bruce Steele »

wdmn

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Re: Basic questions and discussions about melting and freezing physics
« Reply #219 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

Glen Koehler

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Re: Basic questions and discussions about melting and freezing physics
« Reply #220 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

     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.  (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

     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
« Last Edit: October 06, 2020, 08:58:27 PM by Glen Koehler »
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Glen Koehler

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Re: Basic questions and discussions about melting and freezing physics
« Reply #221 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.
« Last Edit: October 06, 2020, 05:34:03 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #222 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.   
« Last Edit: October 06, 2020, 09:00:10 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #223 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).
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Re: Basic questions and discussions about melting and freezing physics
« Reply #224 on: April 30, 2021, 02:47:55 AM »
not sure where to put this, old news, but they have data now ...
I'm not sure either but cross-posting here, more ideas welcome.

Icebreaker's Cyclone Encounter Reveals Faster Sea Ice Decline
https://phys.org/news/2021-04-icebreaker-cyclone-encounter-reveals-faster.html



In August 2016 a massive storm on par with a Category 2 hurricane churned in the Arctic Ocean. The cyclone led to the third-lowest sea ice extent ever recorded. But what made the Great Arctic Cyclone of 2016 particularly appealing to scientists was the proximity of the Korean icebreaker Araon.

For the first time ever, scientists were able to see exactly what happens to the ocean and sea ice when a cyclone hits. University of Alaska Fairbanks researchers and their international colleagues recently published a new study showing that sea ice declined 5.7 times faster than normal during the storm. They were also able to prove that the rapid decline was driven by cyclone-triggered processes within the ocean.

Thanks to the ship's position so close to the storm, Xiangdong and his team were able to explain that cyclone-related sea ice loss is primarily due to two physical ocean processes.

First, strong spinning winds force the surface water to move away from the cyclone. This draws deeper warm water to the surface. Despite this warm water upwelling, a small layer of cool water remains directly beneath the sea ice.

That's where a second process comes into play. The strong cyclone winds act like a blender, mixing the surface water.

Together, the warm water upwelling and the surface turbulence warm the entire upper ocean water column and melt the sea ice from below.

... Although the August storm raged for only 10 days, there were lasting effects.

"It's not just the storm itself," explained Zhang. "It has lingering effects because of the enhanced ice-albedo feedback."

The enlarged patches of open water from the storm absorb more heat, which melts more sea ice, causing even more open water. From Aug. 13-22, the amount of sea ice in the entire Arctic Ocean declined by 230,000 square miles, an area more than twice the size of the state of Arizona.

Liran Peng et al, Role of Intense Arctic Storm in Accelerating Summer Sea Ice Melt: An In Situ Observational Study, Geophysical Research Letters (2021)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092714

... Diagnostic analysis indicates a net energy loss at the ice surface, not supporting the accelerated melting. Although the open water surface gained net heat energy, it was insufficient to increase the mixed‐layer temperature to the observed values. Dynamic analysis suggests that storm‐driven increase in ocean mixing and upward Ekman pumping of the Pacific‐origin warm water tremendously increased oceanic heat flux. The thermal advection by the Ekman pumping led to a warmed mixed layer by 0.05°C–0.12°C and, in consequence, an increased basal sea ice melt rate by 0.1–1.7 cm day−1.



Jim Hunt

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Re: Basic questions and discussions about melting and freezing physics
« Reply #225 on: April 30, 2021, 02:02:24 PM »
I'm not sure either but cross-posting here, more ideas welcome.

In which case I'll cross post my reply!

Icebreaker's Cyclone Encounter Reveals Faster Sea Ice Decline

The Great Arctic Cyclone of 2016? Somebody's been reading "Snow White's" blog!

https://GreatWhiteCon.info/2016/08/the-great-arctic-cyclone-of-2016/

Araon wasn't the only vessel in the path of the storm:

Quote
The crew of the yacht Northabout are currently sailing along the western shore of the Laptev Sea and reported earlier today that:

The sea is calm. Tomorrow a gale 8. But this moment is perfect.

That perfect moment will not last long.

I interviewed David Hempleman-Adams about the succeeding moments once Northabout had returned to the UK. It seems riding out the cyclone was the most frightening experience he had ever had.

Whilst the storm raged Ben Edwards did his homework:

"The most revolutionary thing one can do always is to proclaim loudly what is happening" - Rosa Luxemburg

Glen Koehler

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Re: Basic questions and discussions about melting and freezing physics
« Reply #226 on: May 22, 2021, 10:00:37 PM »
     This commentary on the 2019 melt season is a good reminder/tutorial about the effects of a Dipole weather pattern on ASI Extent, a topic which has already received attention in 2021 and likely even more so in the coming weeks. (bolding added)
-----------------------------------------------------------------------------------------
     "The summer of 2019 was “characterised by an Arctic dipole anomaly pattern of sea level pressure”, explains Zack Labe, a University of California PhD student studying sea ice. He tells Carbon Brief:

     “This essentially means that an area of higher pressure was found on the Canadian side of the Arctic, while a lower pressure was found on the Siberian side of the Arctic.”

     This “dipole” weather pattern has a tendency to accelerate sea ice melting and increase the movement of sea ice out into the Atlantic Ocean, says Labe. The sea ice is pushed out of the Fram Strait – the passage between Greenland and Svalbard – and, hence, is called “Fram export”.

     So, while sea ice extent was at or close to a record low until mid-August (edit - in 2019), a “weakening of the dipole pattern” saw a “switch to stormier/colder conditions over the Arctic”, says Labe. “This allowed 2012 to take the lead,” he adds.

     Such a slowdown in sea ice retreat during this time suggests that “the thinner sea ice cover is now increasingly sensitive to changes in synoptic weather conditions”, notes Labe."
---------------------------------------------------------------------------------------------------
From: Robert Mcsweeney, Sept. 25, 2019. Arctic sea ice summer minimum in 2019 is ‘joint-second lowest’ on record.  Carbon Brief. 
https://www.carbonbrief.org/arctic-sea-ice-minimum-in-2019-is-joint-second-lowest-on-record

« Last Edit: May 23, 2021, 10:35:34 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #227 on: May 22, 2021, 10:12:21 PM »
     Background on another topic that is already important in 2021: Fram Export. (bolding added)
-----------------------------------------------
     "The simulated monthly area export has a significant positive trend of + 10% per decade, explained by wind forcing. The major contribution to the robust trend in area export (is) between June and September.
       Fram Strait ice volume export variability is mainly controlled by ice drift with a dominant role of the Transpolar Drift and, to a lesser extent thickness variability.
       The area export increase reflects increasing ice-drift speed, but is balanced with a reduced thickness over time when it comes to volume export, giving no significant trend in volume export.
       The spatial variability of ice drift indicates that the export influences a large area upstream in the TransPolar Drift stream, and that high volume export events lead to a thinner thickness there.
       The central Arctic is well connected drift-wise to the Fram Strait via the Transpolar Drift while for thickness, the region north of Greenland is dominated and controlled by the Fram Strait ice export."
-----------------------------------------------
Comment - But a stable volume export from a shrinking total ASI volume would be a gradually increasing % of volume lost to Fram Export.

From:  Zamani, B., Krumpen, T., Smedsrud, L.H. et al. Fram Strait sea ice export affected by thinning: comparing high-resolution simulations and observations. Clim Dyn 53, 3257–3270 (2019). https://doi.org/10.1007/s00382-019-04699-z
« Last Edit: May 23, 2021, 10:39:52 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #228 on: May 22, 2021, 10:43:02 PM »
yep, thinner ice requires a larger Fram export area for the same volume, faster drift leaves more open water for an icebreaker to steam without trouble from the Fram to the north pole (in summer).

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Re: Basic questions and discussions about melting and freezing physics
« Reply #229 on: May 22, 2021, 10:49:51 PM »
     Third and final history lesson for context on upcoming 2021 observations.  These excerpts are from an analysis of the impact of the 2012 Great Arctic Cyclone. (bolding added)
---------------------------------------------------------------
     "According to the NCEP/NCAR daily reanalysis sea level pressure, the center of the low-pressure system was well within the sea ice pack, with a minimum central pressure of 974.5 hPa on 7 August.  Simmonds and Rudeva [2012] report a lower minimum central pressure of 966 hPa on 6 August based on the higher resolution Climate Forecast System 6-hourly reanalysis.  During the cyclone's passage, surface winds exceeded 14 m s–1 in some locations, which is within the 99th percentile for August winds in the Pacific sector."

     "Model results indicate that the early August 2012 cyclone did affect the September minimum Arctic sea ice extent but only by a relatively small amount. Nonetheless, the simulated impact of the cyclone on sea ice is strong during and in the immediate aftermath of the cyclone. When the cyclone reached the ice-covered areas of the Pacific sector during 6–8 August, ice melt was enhanced and ice thickness decreased rapidly in much of the Canada Basin. The enhanced ice melt is attributed mainly to an increase in bottom melt due to stronger upward ocean heat transport. "

     "There are some key differences between the conditions leading to the new record set in 2012 and those leading to the previous record set in 2007.  In summer 2012, the simulated ice cover is much thinner and thus more vulnerable to changes in atmospheric and oceanic forcing and easier to shrink. The cyclone was intense enough to cause stronger upward heat transport in a normally well-stratified summer ocean, leading to enhanced bottom ice melt.  Because of the short duration of the storm, ice mass advection is not a significant factor; cyclone-enhanced ice motion only advances ice by additional 9 km d–1 on average.  In the summer of 2007, sustained southerly wind anomalies drove ice away from much of the Pacific sector toward Fram Strait during much of the melting season from July to September, leaving behind a large area of open water and thin ice where ice-albedo feedback caused amplified ice melt."

     "The impact of cyclones on Arctic sea ice is likely to grow if the ice cover continues to thin, given that the largest storm-associated ice volume losses occurred in the most recent years. Summer ice extent will continue to fluctuate from year to year because of natural variability. However, because of the thin ice cover, any year in the future has the potential to set a new record in low ice extent.  Strong summer cyclones or persistent wind anomalies are likely to affect the timing and magnitude of any future record."
------------------------------------------------------------
From:  Zhang, J., Lindsay, R., Schweiger, A., & Steele, M. (2013). The impact of an intense summer cyclone on 2012 Arctic sea ice retreat. Geophysical Research Letters, 40(4), 720–726.  https://doi.org/10.1002/grl.50190.

 
« Last Edit: May 23, 2021, 06:25:26 AM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #230 on: May 23, 2021, 12:24:32 AM »
Thanks for these reminders Glen.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #231 on: May 25, 2021, 02:12:09 AM »

The ice is warmer than the melting point of seawater - when the ice heats up in the summer, the heat conducts down to the base where it melts - the fresher water in the ice mixing with the saltier water below and melting. The simplified thermodynamics are described below. In the real world, the dynamics of melting at the base of the ice are really complicated, particularly as the fresher warmer melt insulates the base of the ice from the higher salinity water below

Consider the surface of the ice is at 0 °C during the summer, and the base of the ice at -1.8°C. The ice has a temperature gradient; the middle of the ice is at -0.9°C. The heat conducts down from the surface. The rate of bottom melt depends on the conductivity of the ice, the thickness, and the transfer of heat to the seawater (assuming it's held at a constant salinity and temp). Thin ice has more bottom melt as it has to conduct heat less far. If the surface of the ice has no surface melting and is held at 0°C, all the ice would still melt out from the bottom melt.

When the temperature at the surface falls to, say, -5°C, the heat from the ice middle at -0.9°C transfers upwards and downwards and cools until it reaches -3.4°C.
     Ditto thanks for that explanation Rox.  Describing the fact that as the ASI (on average) gets thinner, the required temperature to melt ASI (on average) shifts to a lower threshold illuminates a new perspective in my dim mind.
     A 0.5C (pick any number you like) lowering of the average melt temperature threshold (e.g. from ice melting at -1.8C instead of having to reach -1.3C to cause melting) would have the same effect as a +0.5C rise in Arctic Ocean water/surface air temperatures would have had if the ASI had remained the same. 
     With the combination of a warming Arctic AND thinning sea ice, the two trends combine to cause melt at a rate greater than either effect (thinning, temperature rise) would have alone.
     Is this logic correct? 
     Nothing new in saying that as the ASI thins it is less resistant to melt.  But your explanation of  the energy transfer change for thinner ice highlights this double whammy concept. 
      I guess there's nothing new in that either, except to my brain it highlights how the ASI is in peril from essentially getting hit from two forcings at once as both trends continue on their respective trajectories.

      This perspective also brings insight into Peter Wadham's "Just goes Poof" description of the end-game scenario.  It seems that the effect of thinning on the melt temperature threshold is relatively minor and very slowly incremental as the ice transitions from 2.0 meter to 1.5 to 1.0 to 0.5 M.  As as the ice is >0.5 M thickness it is the continuation and gradual increase of elevated Arctic temperatures that drive the change in the ASI statistics (Extent, Area, Thickness, Volume).  While extremely rapid in a geo-paleoclimatic frame of reference, from the perspective of an ASIF fan watching from the cheap seats, it progresses relatively slowly from year to year.

      But another force emerges to accelerate the pace as thickness gets below about 0.5 M.  At that late stage the formerly rather insignificant cumulative effects from the decline in melt temperature threshold, the distance heat has to travel through the ice, and in the amount of energy required to melt the remaining thickness (from a combination of the amount of ice in that thickness and its temperature dynamics per unit) will become increasingly more important in determining the ice melt response within a single melt season.
      Because of the acceleration provided by those late-stage additional melt rate drivers, the time to go from 2.0 to 1.5 to 1.0 to 0.5M will be on one trajectory, but that final 0.5M, and especially the last 0.25 M, would be on a much steeper and faster trajectory.  As a result, removing the final 0.5M will take a lot less time than it took to go from 2.0 to 1.5M average thickness. 

      Ice scientists have probably shown this in a chart somewhere, but all I could find in a superficial search was one chart that was really about a broader question and just happened to include a few data points showing increased melt rate as ice thinned down to about 0.5M. 

      Note that in the 1st chart shown below, which is the data source for the 2nd chart, the negative "Growth Rate" in summer  = summer Melt rate.  The X-axis on the chart is meters of ASI thickness.  --- Yes, Virginia, there is a Santa Claus.  And at one time he and Mrs. Claus relaxed during the summer on 15 Meter thick ASI.  Now they have to live on a houseboat.

     Chew on the fact that not that long ago there was 15M  thick summer sea ice in the Arctic.  And the chart in the Zhang and Rothrock source article has this annotation: "The ice growth rates for ice thicker than 15 m are not plotted."  So they had observations for SUMMER Arctic sea ice THICKER than 15 meters!  Now there is precious little ASI thicker than 4M.
 
     The 2nd chart just highlights the melt rate for a few of the thinnest ice data points from the 1st chart.  The data points in the 2nd chart are from the upper solid line of the 1st chart, the lower dotted and dashed lines in the 1st chart are irrelevant for this discussion.
« Last Edit: May 26, 2021, 01:13:19 AM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #232 on: May 25, 2021, 04:21:43 AM »
     At risk of beating this to death, here is a counter-argument to the previous post.  If there is a great acceleration of ice loss as Thickness, and therefore Volume, approach zero, we should see that in the Volume records for the individual seas as they previously reached the stage of melting out entirely.  One way to see if that is the case is to look at Gerontocrat's Volume charts for individual seas (posted about this time in 2020).  If they hit a "Poof" phase near melting out, I would expect to see a gradual Volume decline, then an accelerated decline as they approached and reached zero Volume.

    But I do not see that pattern in any of the individual sea Volume charts below.  This is a crude way to evaluate the "Poof" hypothesis.  Crunching the Volume numbers for those individual seas might reveal evidence for an acceleration of ASI loss as a sea approaches zero. 

     Maybe the Gero charts do not demonstrate an accelerated final drop-off as a sea nears zero summer ice Volume because year-to-year variability is still the larger and controlling factor.  Thus, when a sea has a strong melt year, it reaches zero, and the noisiness of year-to-year variability obscures a final stage acceleration effect.  If so, perhaps decadal average Volume charts ofr the 1980s, 1990s, 2000s, and 2010s with less year-to-year variation masking the trend and covering a longer span of years than just 2005-2019 would show an end-game acceleration.

     But also true that "Poof" loss does seem to occur at the scale of large floes, for example this vintage ASIF post from 2014 https://neven1.typepad.com/blog/2014/08/poof-its-gone.html
And finally this film noir Nick Danger meets ASI future post mortem by Gero https://forum.arctic-sea-ice.net/index.php/topic,2348.msg284450.html#msg284450
« Last Edit: May 26, 2021, 01:09:23 AM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #233 on: May 25, 2021, 02:30:19 PM »

The ice is warmer than the melting point of seawater - when the ice heats up in the summer, the heat conducts down to the base where it melts - the fresher water in the ice mixing with the saltier water below and melting. The simplified thermodynamics are described below. In the real world, the dynamics of melting at the base of the ice are really complicated, particularly as the fresher warmer melt insulates the base of the ice from the higher salinity water below

Consider the surface of the ice is at 0 °C during the summer, and the base of the ice at -1.8°C. The ice has a temperature gradient; the middle of the ice is at -0.9°C. The heat conducts down from the surface. The rate of bottom melt depends on the conductivity of the ice, the thickness, and the transfer of heat to the seawater (assuming it's held at a constant salinity and temp). Thin ice has more bottom melt as it has to conduct heat less far. If the surface of the ice has no surface melting and is held at 0°C, all the ice would still melt out from the bottom melt.

When the temperature at the surface falls to, say, -5°C, the heat from the ice middle at -0.9°C transfers upwards and downwards and cools until it reaches -3.4°C.
Thanks for this Rox! This helped a lot making me understand the melting process a little better. I should know by now that I shouldn't simplify things too much.  :-\

Let me see if I understand it correctly now...

Basically you have a mix of MYI and FYI, and FYI contains more salt, so it has a lower melting temperature, thus making it the first ice to melt ice out while the whole thing heats up in summer, leaving behind the MYI to melt out last?

During freezing season the MYI gets all mixed up with the FYI ice again, and the whole thing repeats...

But I assume the process is a little different when the ice is covered with melt ponds? When they heat up above 0°C, they will melt the MYI on top?

And how is the conductivity between MYI and FYI? In water a difference in salinity creates a boundary. Does that boundary exist in ice as well? Does a difference in salt content impede conductivity?
« Last Edit: May 25, 2021, 02:43:45 PM by Freegrass »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #234 on: May 25, 2021, 04:17:03 PM »
As far as I know, the definition of MYI vs. FYI is in 2D, not 3D, meaning a piece of ice can only be FYI or MYI, regardless of the various layers making it up and their history of freezing.

Also a comment on Rox's post - I thought that when the ice is briny (esp. FYI) and the snow on top has melted and drained, the temp on top of the ice can be lower than 0C. I could be wrong though, maybe during the melting and draining of the top snow the salt in the ice is also drained away?

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Re: Basic questions and discussions about melting and freezing physics
« Reply #235 on: May 25, 2021, 06:00:17 PM »
Thanks for moving my post here Oren. Probably better...

As far as I know, the definition of MYI vs. FYI is in 2D, not 3D, meaning a piece of ice can only be FYI or MYI, regardless of the various layers making it up and their history of freezing.

That would seem weird to me. When MYI thickens again in winter, it collect FYI, right? And then when the ice moves around and gets pilled up, the MYI will get mixed in with FYI, no? But you are saying that even when it's mixed up like that, you still call it MYI? Because it contains ice of multiple years?

Regarding my question; When this mix of MYI heats up like Rox explained, I presume the youngest ice - with the highest salt content and lowest melting temperature - would melt out first? Leaving the oldest ice behind to melt out last?
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Re: Basic questions and discussions about melting and freezing physics
« Reply #236 on: June 03, 2021, 06:18:10 AM »
     This reply is to a discussion about a latitude effect on Arctic solar radiance that emerged on the Freeform thread, but seems to fit better with the melting physics thread.  If not, Oren can do his moderating magic.

From JAXA Extent report for June 29 2020
<snip> On average 50.3% of melting from maximum to minimum done
     The Arctic insolation graph below was posted by A-Team last summer.  It is solar energy at surface, not top of the atmosphere, so incorporates atmospheric absorption from lower sun angle at higher latitudes as discussed recently in the Freeform thread.

     Comparing Gero's June 29 JAXA 50% Extent loss date to the solar insolation curve shows that it is less than 10 days past the date of peak insolation.  I expected a much longer lag.  For example, the date of the annual terrestrial surface temperature peak varies around the world, but is around July 20 for many, if not most, locations.  Thus a 30-day lag.  The date for peak ocean surface temperature is even later.  For example, it is around August 8 - 15 for the coastal waters of Northeastern U.S., thus a 50-60 day lag. (I don't know about elsewhere.  I suspect it is even later for the Caribbean/Gulf of Mexico given that the peak period of southeast U.S. hurricane season, driven by ocean surface heat, doesn't begin until August 15).

     At first I thought that the short lag between peak insolation and Extent loss has more to do with the vagaries of Extent as a rather flukey (no disrespect, and it is our most direct and frequent monitor!) measurement of ASI than the energetics of solar radiance.  But I may be incorrect in assuming that the maximum loss rate coincides with the 50% loss date.

    June 4 SECOND Corrections/Edits since original post: I did a quick look at some PIOMAS CAB Volume data.  It shows a maximum loss RATE (using 15-day average losses to avoid anomalous short term blips from a storm etc.) on July 7, 2016, June 29, July 7, 2017;  June 26 July 4, 2018; and ~(very broad peak) June 25 June 30, 2019.  Revision needed because the original dates were based on the 15-day leading ** not date-centered** average of day to day volume reduction. I added 2016 just to have one more replicate.

     The lesson seems to be that immediate solar radiation controls the rate of ASI Volume loss, with about a 15 day lag from peak insolation to date of peak day to day volume reduction.  Thus the Volume less trajectory does not show a long lag expected if cumulative warming of the ocean water was the driving factor behind Volume reduction, i.e. melt.  That interpretation for the prominence of solar radiation as the direct driving factor controlling the rate of ice melt also gives more credence to melt pond momentum and albedo reduction during the period of peak insolation as an important influence.
« Last Edit: June 05, 2021, 06:07:43 AM by Glen Koehler »
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Glen Koehler

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Re: Basic questions and discussions about melting and freezing physics
« Reply #237 on: June 03, 2021, 07:50:55 AM »
     Another carryover from the Freeform thread:
gero : 'I wonder if there is much difference in the effectiveness of insolation on sea ice melt between a nice flat ice sheet and a broken up ridged ice landscape?'

I'think I've asked the same question here every year , so far without reply .. may you have greater success .. b.c.
 
In fact ..
Hi F. Tnioli .. I have been raising a similar hypothesis here for some years .. low angle sun melting near vertical ice faces .. my thoughts were mostly relating to the exposed fracture surfaces as they seemed to increase in number over the years , Last year I was remarking on the obvious 360' melt and run-off on the steep slopes around an mini island ice sheet N of russia while the horizontal surface was unaffected . b.c.
     
So jun6 to jul1 is practically the same surface radiation from 70N-90N. Interesting.
and may13 to jul29 fro 80N to 90N
So all those statements about the pole being the hardest to melt out may need to be revisited?

Perhaps it's more like the centre of inaccessibility is hardest to melt out but that tends to drift towards the pole every year.

Reminds me of this thread I started nearly 2 years ago.

https://forum.arctic-sea-ice.net/index.php/topic,2814.msg215539.html#msg215539

I found a useful website (URL below) which makes use of an interactive slider to change latitude and illustrate :

1) the intensity of direct radiation in W/m² throughout the day 0 to 24 hrs. It is the amount of power that would be received by a tracking concentrator in the absence of cloud.
 
and

2) the average daily solar insolation as a function of latitude. kWh/m2/day.

Regarding sea ice it is the second chart which is most useful. The chart shows 3 curves - the incident solar insolation, the horizontal solar insolation and the solar insolation on a titled surface

I have attached a couple of stills for this second chart. I have set the tilted surface at 30° (which could be taken as representative of a ridged surface at 30 degree angle to the horizontal).

The first still is with slider set to 67 N. At summer solstice this gives a total of 9 kWh/m2 on a horizontal surface

Curiously this actually increases as you go a little further north, up to about 71.5 N. At summer solstice it is now circa 9.5 kWh/m2

But thereafter it falls back. Third image is at 80 N and now it is 8 kWh/m2

Lastly at 90N it is down to only 6.5 kWh/m2

These charts substantiate what in practice we have seen i.e. that it is hard to melt the ice inside 85 N.

Try out the sliders here :

https://www.pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation
     At risk of blundering into a topic I know almost nothing about and thus uninhibited from knowledge-based self-constraint (like Repugnican politicians here in the U.S. for whom facts and objective reality are left-wing constructs and mere impediments to self-service disguised as ideology, but I digress....), I think the slider link shared by Niall addresses your question.

     The charts below give values from the sliders for surface solar radiation at 80N with tilts of 15, 30 and 45 degrees, as indicated by the green line.  The blue line shows incident radiation for a flat surface.  The tilted surface is assumed to face the equator, i.e. due South from 80N.

     With latitude set at 80N, the green line maxed at a tilt of 57 degrees then started getting lower again.  At 80N at noon on June 20/21, the sun is 33.5 degrees above the horizon in the south, so adding 56.5 more degrees gives you 90 and thus perpendicular to the sun's rays.  Thus, the degree of tilt for max solar radiation varies with latitude. 

     Bottom line is that relative to a flat surface, at 80N a 15 degree tilt to the south increases incident solar radiation at the June peak (not all year) by about 50% (because you have increased the incident angle at noon by about 50% from 33.5 degrees for a flat surface to 33.5 +15 = 48).  But a 33.5 degree tilt does not double the incident radiation so there's more to it than the incident angle at noon on June 20.

     Setting the slider at full 90N shows the max incident radiation on June 20 with a tilt of 66.5 degrees.  Which makes sense because with the Earth's tilt at 23.5 degrees, on June 20 at 90N, a surface tilt to add 66.5 more degrees makes the surface at 90 degrees and perpendicular to the sun's rays at noon.

     Adjusting the latitude for different tilts shows that the higher the latitude, the bigger the gain at Peak solar radiation (i.e. June 20) from increasing the tilt above 0 degrees (flat).
« Last Edit: June 03, 2021, 04:22:50 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #238 on: June 18, 2021, 08:40:21 AM »
https://tc.copernicus.org/articles/15/2575/2021/
Interannual variability in Transpolar Drift summer sea ice thickness and potential impact of Atlantification
Belter, H. J., Krumpen, T., von Albedyll, L., Alekseeva, T. A., Birnbaum, G., Frolov, S. V., Hendricks, S., Herber, A., Polyakov, I., Raphael, I., Ricker, R., Serovetnikov, S. S., Webster, M., and Haas, C.:  The Cryosphere, 15, 2575–2591, https://doi.org/10.5194/tc-15-2575-2021, 2021

Abstract
Changes in Arctic sea ice thickness are the result of complex interactions of the dynamic and variable ice cover with atmosphere and ocean. Most of the sea ice exiting the Arctic Ocean does so through Fram Strait, which is why long-term measurements of ice thickness at the end of the Transpolar Drift provide insight into the integrated signals of thermodynamic and dynamic influences along the pathways of Arctic sea ice. We present an updated summer (July–August) time series of extensive ice thickness surveys carried out at the end of the Transpolar Drift between 2001 and 2020. Overall, we see a more than 20 % thinning of modal ice thickness since 2001. A comparison of this time series with first preliminary results from the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) shows that the modal summer thickness of the MOSAiC floe and its wider vicinity are consistent with measurements from previous years at the end of the Transpolar Drift. By combining this unique time series with the Lagrangian sea ice tracking tool, ICETrack, and a simple thermodynamic sea ice growth model, we link the observed interannual ice thickness variability north of Fram Strait to increased drift speeds along the Transpolar Drift and the consequential variations in sea ice age. We also show that the increased influence of upward-directed ocean heat flux in the eastern marginal ice zones, termed Atlantification, is not only responsible for sea ice thinning in and around the Laptev Sea but also that the induced thickness anomalies persist beyond the Russian shelves and are potentially still measurable at the end of the Transpolar Drift after more than a year. With a tendency towards an even faster Transpolar Drift, winter sea ice growth will have less time to compensate for the impact processes, such as Atlantification, have on sea ice thickness in the eastern marginal ice zone, which will increasingly be felt in other parts of the sea-ice-covered Arctic.

.
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gerontocrat

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Re: Basic questions and discussions about melting and freezing physics
« Reply #239 on: June 18, 2021, 12:49:06 PM »
Hullo Glen,

The extract in your post above makes me wonder if the PIOMAS model is picking up this reduction in ice thickness for the volume measurements.

It also makes me wonder about consequences of increased ice mobility and reduced thickness, e.g. the disintegration of the ice sheet into separated floes seen this year twixt 80 and 85 North on the Atlantic Front.

and (speculation) collapse vs. slow transition.
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Re: Basic questions and discussions about melting and freezing physics
« Reply #240 on: June 18, 2021, 01:55:38 PM »
Very important paper, thank you Glen.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #241 on: June 20, 2021, 05:29:19 PM »
Uniquorn, Just to make sure I know what I got wrong. I still contend that white is is more reflective than meltponds and that when meltponds drain the ice becomes whiter.
The part where I am wrong is that what light does get through only heats the ice but not the water below it ?
Could someone tell me more about IR and if IR can penetrate the ice like PAR or UVR.

     Water vapor in the atmosphere is largely transparent to and does not interact with or block downstream shortwave solar radiation like PAR and UVR.  But that atmospheric water vapor does resonate with and absorbs the energy when it is reflected back up as longwave IR.  Unless being frozen changes the interaction of water molecules with radiation wavelengths, that implies that IR would not penetrate ice, but would instead be absorbed by it.  Just my guess by extrapolating from the interaction of water vapor as a potent GHG with radiation wavelengths to ithe interaction of ice to those wavelengths.  But the vapor vs. frozen condition may invalidate that extrapolation. 
« Last Edit: June 20, 2021, 07:36:51 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #242 on: June 20, 2021, 05:54:18 PM »
Glen, So IR wouldn’t penetrate seawater either ? It must heat the surface of ice or seawater to some depth . From my personal experience sunlight heats seawater but largest effect is first foot or two of depth. From thousands of hours under the water or swimming on the surface back to the boat.
 Excuse my ignorance on how sunlight interacts with the ice or seawater, seems pretty basic. I have a feeling I am not the only one with some misconceptions.

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Re: Basic questions and discussions about melting and freezing physics
« Reply #243 on: June 20, 2021, 07:09:05 PM »
Water has the transparency of a brick at almost every wavelength except visible.

That, which is not transparent, absorbs (energy) - if it doesn't reflect it. Water has high absorption and virtually no reflectance in near infrared wavelengths range and beyond.



Note: The lowest part of the water absorption spectrum is in the visible portion of the spectrum. UV light can penetrate water fairly well.
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Re: Basic questions and discussions about melting and freezing physics
« Reply #244 on: June 20, 2021, 07:27:40 PM »
Vox - So being frozen vs.liquid vs vapor has no effect on water reflection/absorbance of different wavelengths?  The only basis I have is water vapor, so wondering if that basis applies to water molecules in liquid or frozen state.

bruce - My guess is that seawater absorbs the IR at the surface and that warming farther down is from heat diffusion.  But somebody who actually knows what they are talking about might correct that.
« Last Edit: June 20, 2021, 07:39:08 PM by Glen Koehler »
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Re: Basic questions and discussions about melting and freezing physics
« Reply #245 on: June 20, 2021, 08:06:38 PM »
Ice and liquid water have nearly identical absorption spectra (red, blue) water vapor (green) is different. But they all absorb in IR



Ice will reflect in visible, absorb in IR
Water is transparent in visible, absorbs in IR
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Re: Basic questions and discussions about melting and freezing physics
« Reply #246 on: June 20, 2021, 08:31:13 PM »
     Спасибо Vox!
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Re: Basic questions and discussions about melting and freezing physics
« Reply #247 on: June 21, 2021, 08:07:15 AM »
I posted in the 2021 Melting season thread about a possibly pertinent article I stumbled across in Physics Today about a satellite based cloud effects measuring project, "The impact of polar clouds (2015)", I don't remember seeing this mentioned here in the Forum, but that may be due to senility. Anyway, the article is very interesting and the following image (Figure 2) was something of an eye opener for me. It is based on average measurements for the years 2007-2010 and shows the net effect of clouds during four representative months.

Unfortunately, the pole hole is very prominent, but note that in the July picture, the net effect over ice (Greenland as well as the sea ice in CAA and the Beaufort/CAB) is definitely positive, i.e. clouds cause net warming over ice even in july. A bit of a surprise for me and perhaps for some others.

The cooling effet of clouds is clear during summer over ice-free areas, but remember that these images do not show the energy being transmitted to the Arctic by the oceans, only the net effec of clouds on insolation. Also, the cooling effect of clouds over ice-free areas is strongest around the solstice (as should be expected), but gets less and less prominent as we enter the main melting season, being close to neutral in September over the ocean but strongly positive over the remaining ice.

Quote
In May ... it is clear that overall clouds warm the ice sheets, but to a lesser magnitude than earlier months. They also begin to slightly cool the Eurasian continent and Alaska. By July ..., clouds strongly cool the entire Arctic region, save for Greenland and the remaining Arctic sea ice. September ... shows that the clouds have an approximately neutral effect (neither heating nor cooling the surface) over much of the Arctic, but with strong warming over Greenland and the remaining ice sheet. During Arctic winter months, as previously mentioned, there is no incoming solar radiation, and thus no CSWF. Clouds serve only to warm the surface in these months.
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binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #248 on: June 27, 2021, 09:44:46 AM »
To my mind, the discussions here tend to extend too much value to the effects of insolation on ice, while forgetting the effects of oceanic heat transfer and wind heat transfer.

This is not to ignore the fact that the melt season happens following maximum insolation, during the Northern Summer, but that is because the entire hemisphere recieves a lot more energy, much of which tends to be transported north, particularly over the Atlantic.

So what has the biggest efffect on melting - insolation, ocean heat transport or air heat transport? If the latter two are sizeable enough, the net effect of any cyclone would always be negative to the ice, seeing as how stronger winds bring more air transport, and turbulence enhances release of ocean heat.

A recent paper termed An Improved Estimate of the Coupled Artic Energy Budget (Mayer et al 2019) is very interesting in this context.

The image below seems to indicate that air transport seems to be the largest contributor to the energy balance which is a surprise to me, I would have thought the ocean was more important.

Surprisingly, air heat transport is greatest during winter, perhaps due to increased storminess. The overall heat loss in winter from the Arctic is overwhelmingly from the atmosphere, since the ocean is hidden beneath the ice.

But looking at the figures and trying to understand them leaves me with more questions than answers. What is the biggest contributor to ice melt in this context? Is it direct insolation, is it ocean heat transfer or is it atmospheric heat transfer?

I do not pretend to understand all the terms in the following image, "Energy storage and flux terms (in W/m2) for the Arctic Ocean domain. ... The arrows are scaled by the square root of their magnitude"

Rad/TOA = Radiaton Top Of Atmosphere
AET = Atmospheric (total) Energy Tendency
Fs = Net Surface Energy Flux
MET = Melt Energy Tendency (latent heat of fusion released or required)
OHCT = Ocean Heat Content Transfer
2ry = Secondary, snow and land
Fa = Atmospheric Energy Transport
Fo = Ocean Heat Transport
Fi = Latent Heat Transport, Ice (e.g. through Fram export)
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binntho

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Re: Basic questions and discussions about melting and freezing physics
« Reply #249 on: June 27, 2021, 10:25:07 AM »
Another interesting paper that seems to support both views - insolation is the biggest contributor, but occasional wind events cause significant heat transport from ocean.

Energy budget of first-year Arctic sea ice in advanced stages of melt (Hudson et al 2013)

From the abstract:

Quote
During an 8 day drift in July–August 2012 in the Nansen Basin, all components of the energy budget of melting first-year sea ice were observed. Absorption of solar radiation by the ice and ponds was the largest source of energy to the ice at almost all times during the drift. However, oceanic heat flux also provided significant heating and dominated during one wind event. Longwave fluxes provided a relatively small cooling effect, and atmospheric heat fluxes were negligible.

Open ocean accounted for 5% of the general area, but even so, a strong wind event seems to have caused enough turbulence and upwelling to release a lot of oceanic heat:

Quote
In the data set presented here, oceanic turbulent heat flux provided, on average, 13 W  m−2 of energy to the ice, 20% of the total, and at times, it became the most significant heat source, climbing to over 70 W  m−2. The largest heat fluxes were measured during a relatively long period (about 30 h on 30–31 July) with strong winds (8–12 m  s−1

In other words, 20% average from ocean, 80% from the sun, on a FYI floe with extensive melt ponding. But during a strong wind event (i.e. a possible cyclone), ocean heat flux rose more than five fold above average, to 70 W/m2, more than the average shortwave insolation at 60 W/m2.

Which tells me that direct melt is probably very similar under clear skies and during a cyclone. Ocean heat transport increases sufficiently due to increased winds to outweigh the loss of insolation.
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