Basic questions and discussions about melting physics

[johnm33]

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.

[interstitial]

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]

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.

[Phil.]

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]

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.

[The Walrus]

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,

[interstitial]

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 


 


























 

[binntho]

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.

[binntho]

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.

[The Walrus]

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.

[binntho]

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?

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!

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.

[binntho]

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.

[oren]

Maybe it would be better to read some scientific literature about it?

[P-maker]

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]

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.

[binntho]

Thus, size matters!

What about quality? 

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

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.

[oren]

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.

[Tor Bejnar]

What Causes Ice to Turn White?
I don't know the source, but it was at the top of my internet search ...

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

...
 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.

[Bruce Steele]

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

[wdmn]

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]

  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

[Glen Koehler]

....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.

[Glen Koehler]

      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.   

[binntho]

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).