Basic questions and discussions about melting and freezing physics

[binntho]

Indeed. But why does the ice freeze much faster when it is thinner (< 50cm) or perhaps it doesn't?

[FredBear]

It is slow to start because air temperature needs to be about -10^oC before mixing, etc., overcome "inertia" before refreeze starts. Once the freeze starts the surface can cool more rapidly because of the damping effect of the ice and the season is likely to be cooling further. More heat is lost because the ice is thin and thickness can grow rapidly.

As the ice thickens the insulation increases (the heat gradient is stretched further) and the rate of thickening will decrease. Once the initial ice cover has formed snow and ice crystals can also accumulate on the surface and start forming even more insulation.

[kassy]

Indeed. But why does the ice freeze much faster when it is thinner (< 50cm) or perhaps it doesn't?

It freezes fine either side of 50 cm. Basically it is just a thermal flux. Cold air sucks energy out of the water until it freezes. Now if the top is frozen the rest of the freeze is going to be on the bottom. Somewhere over 2Ms it gets so thick that this stops and you need collisions to get it thicker.

The slow transition never was about what happens around what happens at 50 cm. It is about the difference between ice covered oceans and oceans that are open and then refreeze.

[uniquorn]

Likely that it will freeze top and bottom till it has enough freeboard or area to prevent waves and spray washing over it.

[binntho]

Kassy, that was exactly what FredBear said did not happen - it is not the cold air that sucks out the heat, but radiatitive loss from the surface, that is the main cause of cooling.

In fact, from FredBear's description, the transition from fast-pre-50 to slow-post-50 freeze is more contingent than inbuilt.

[binntho]

Likely that it will freeze top and bottom till it has enough freeboard or area to prevent waves and spray washing over it.

Top freeze can hardly count for more than a few mms if it is based on putative splashes from nearby open water.

[Jim Hunt]

In fact, from FredBear's description, the transition from fast-pre-50 to slow-post-50 freeze is more contingent than inbuilt.

How do you like the sound of Alan Thorndike's "Sea ice thickness as a stochastic process"?

The thickness h of sea ice varies in a complicated, and probably unpredictable way as a function of space and time.

See also the final reference.

[binntho]

In fact, from FredBear's description, the transition from fast-pre-50 to slow-post-50 freeze is more contingent than inbuilt.

How do you like the sound of Alan Thorndike's "Sea ice thickness as a stochastic process"?

The thickness h of sea ice varies in a complicated, and probably unpredictable way as a function of space and time.

See also the final reference.

So what happens to the "slow transition" theory if rates of thickening (and melting?) behave stochastically and may even be (the horror ... the horror ... ) random? This feels like something straight from the heart of darkness - if it wasn't so damn hot here I'm sure I would be shivering!

[kassy]

Kassy, that was exactly what FredBear said did not happen - it is not the cold air that sucks out the heat, but radiatitive loss from the surface, that is the main cause of cooling.

In fact, from FredBear's description, the transition from fast-pre-50 to slow-post-50 freeze is more contingent than inbuilt.

Let me try this the other way around. The old regime had ice all over the ocean. Bits melted but overall much more of the water was covered by thick ice. If there is already ice this isolates the amount of energy coming out of the water.

If it is well over 50 CM you can skip this step every year:
It is slow to start because air temperature needs to be about -10oC before mixing, etc., overcome "inertia" before refreeze starts. Once the freeze starts the surface can cool more rapidly because of the damping effect of the ice and the season is likely to be cooling further. More heat is lost because the ice is thin and thickness can grow rapidly.

If it is somewhere between 150-200 CM much of this is already done:
As the ice thickens the insulation increases (the heat gradient is stretched further) and the rate of thickening will decrease.

The theory is simply that a lot of energy that went into melting the ice now just radiates out to space when it is open water or when it is refreezing and this change will slow melt down compared to when the thick multiyear ice died.

And yes what matters is the energy transfer through the whole system so forgive my oversimplification above.

[binntho]

Kassy, the assumption that thick ice isolates the energy coming out is exactly what we are debating. Ice is not necessarily an insulator, particularly when it comes to radiative forcing.

And if ice is not an insulator, then the rate of refreeze is not related to the thickness of the ice. It becomes a contingent rather than a necessary result of a lot of different circumstances.

EDIT: In other words, the ice should not be a barrier to outgoing thermal radiation from the underlying ocean. The fact that experience tells us it is a barrier is contingent, depending on the presence of snow, bubbles, fractures etc.

[uniquorn]

Likely that it will freeze top and bottom till it has enough freeboard or area to prevent waves and spray washing over it.

Top freeze can hardly count for more than a few mms if it is based on putative splashes from nearby open water.

putative    adjective [ before noun ]   formal
generally thought to be or to exist, even if this may not really be true:

putative in British English    adjective
1. (prenominal)
commonly regarded as being
the putative father
2. (prenominal)
considered to exist or have existed; inferred
3.  grammar
denoting a mood of the verb in some languages used when the speaker does not have direct evidence of what he or she is asserting, but has inferred it on the basis of something else

https://earthobservatory.nasa.gov/features/SeaIce

The Sea Ice Life Cycle

When seawater begins to freeze, it forms tiny crystals just millimeters wide called frazil. How the crystals coalesce into larger masses of ice depends on whether the seas are calm or rough. In calm seas, the crystals form thin sheets of ice, nilas, so smooth that they have an oily or greasy appearance. These wafer-thin sheets of ice slide over each other and form rafts of thicker ice. In rough seas, ice crystals converge into slushy pancakes. These pancakes slide over each other to form smooth rafts, or they collide into each other, creating ridges on the surface and keels on the bottom.

Regarding radiation flux, there is a lot of detail here:

Impacts of snow and surface conditions on radiation fluxes through Arctic sea ice during different seasons
Philipp Anhaus
https://epic.awi.de/id/eprint/55951/1/anhaus_thesis-pdfa_2022.pdf

Abstract
Sea ice and its snow cover play a key role within the climate and ecosystem. Due to global environmental changes which are amplified in the Arctic Ocean, its sea-ice cover will primarily consist of thin and young sea ice with a reduction in extent. In particular, the area where snow accumulates reduces and the fraction of melt-pond covered sea ice and of openings in the sea-ice cover such as leads increase. Those changes of the surface conditions strongly influence the partitioning of solar radiation.
The main objective of this dissertation was to establish relationships between the surface conditions that are observed and expected to dominate in the future Arctic and under-ice radiation. A deeper and broader knowledge of such relationships is especially necessary in spring and autumn during which the under-ice radiation can have significant impacts on the annual energy budget. To achieve that, field measurements collected using a variety of instruments during three campaigns for three different sea-ice types, locations, and seasons were analysed and interpreted.
A main result was to derive a new parametrization for snow depth retrieval from spectral under ice-radiation measurements. This was successfully achieved with an accuracy of approximately 5 cm for two ice types, in two locations, during two seasons.
In contrast to the established theory that melt ponds act as bright windows to the underlying ocean, it was possible to document and analyse cases where a thicker snow cover accumulated on melt ponds compared to on adjacent bare ice. This resulted, surprisingly, in lower levels of under-ice radiation underneath the melt ponds than underneath bare ice.
New analyses of relationships between thermodynamics and optics of a refreezing lead and thin ice suggest that radiative transfer in thin ice is often not accurately accounted for using bulk formulations, as they are applicable for thicker ice. The initial states of the lead’s opening and refreezing need to be treated separately and cannot generally be considered windows into the ocean. This dissertation extended our knowledge of the relationships between snow and surface conditions and under-ice radiation. The results point towards impacts on sea-ice energy balance, ocean heat content, thermodynamic ice growth, and ice-and ocean-associated ecosystem activity

[Phil.]

Kassy, the assumption that thick ice isolates the energy coming out is exactly what we are debating. Ice is not necessarily an insulator, particularly when it comes to radiative forcing.

And if ice is not an insulator, then the rate of refreeze is not related to the thickness of the ice. It becomes a contingent rather than a necessary result of a lot of different circumstances.

EDIT: In other words, the ice should not be a barrier to outgoing thermal radiation from the underlying ocean. The fact that experience tells us it is a barrier is contingent, depending on the presence of snow, bubbles, fractures etc.

Heat loss from the underlying water is via conduction through the ice which is a slower process than the loss from the surface via convection and radiation so it is the rate limiting step.  As the ice gets thicker bottom freeze gets slower and slower.

[binntho]

Kassy, the assumption that thick ice isolates the energy coming out is exactly what we are debating. Ice is not necessarily an insulator, particularly when it comes to radiative forcing.

And if ice is not an insulator, then the rate of refreeze is not related to the thickness of the ice. It becomes a contingent rather than a necessary result of a lot of different circumstances.

EDIT: In other words, the ice should not be a barrier to outgoing thermal radiation from the underlying ocean. The fact that experience tells us it is a barrier is contingent, depending on the presence of snow, bubbles, fractures etc.

Heat loss from the underlying water is via conduction through the ice which is a slower process than the loss from the surface via convection and radiation so it is the rate limiting step.  As the ice gets thicker bottom freeze gets slower and slower.

And why not through radiative thermal conduction? Ice has a similar transparency to water, so heat can radiate through it.

Of course there is no convection in ice, but I seem to remember that the underlying sea is highly stratisfied with limited convection so is there really so much of a difference?

[binntho]

uniquorn, yes I know what "putative" means and used it deliberately since I don't think top freeze from sea spray is a real thing except in very limited circumstances.

The rest of your post, on the effect that surface condition have on radiative flux through ice, is along similar lines to what I was thinking earlier while dining on roast goat and drinking local beer - once I have my facculties (hicc!) back in order I'll comment further on this very interesting topic.

[oren]

I think we have seen clearly in charts uniquorn and others have posted in the buoys threads over the years, the gradient of temperatures through the ice and snow, what it appears like in deep winter when air temps are -35C, and how it changes during spring.
In deep winter, the ice is clearly an insulator as the ocean temp is -1.8, with the ice becoming colder and colder the further one goes up. When the snow layer is reached, again we see colder and colder temps, but for each cm of snow there is a much larger gradient than for each cm of ice, showing how snow is a much better insulator.
IMHO, it doesn't matter that much if the air is what gets the top of the ice/snow to be cold, or the dark sky gets both the air and top of the ice/snow to be cold. The result is not very dissimilar. What does matter is that when the ice is thicker (and obviously, when there is snow and when the snow is thicker) the rate of cooling of the bottom of the ice decreases (rate of loss of energy is perhaps more appropriate), and the rate of bottom freezing is slowed. This follows both from the gradient charts and from the empirical formulas for ice thickening.
During spring, the ice top warms, and we get a cold core with two warmer fronts above and below. This continues until the core equilibrates with the top (typically near 0) and the bottom (still at -1.8 ). The core maintains its cold temp longer when it is thicker, again showing the property of ice as an insulator (at least in my layman terms).
Sorry I cannot provide an appropriate sample buoy chart, lacking the time, but it can be found in the buoy threads.

[uniquorn]

Thermodynamic growth from https://epic.awi.de/id/eprint/55951/1/anhaus_thesis-pdfa_2022.pdf for ref.

[Phil.]

And why not through radiative thermal conduction? Ice has a similar transparency to water, so heat can radiate through it.

Of course there is no convection in ice, but I seem to remember that the underlying sea is highly stratisfied with limited convection so is there really so much of a difference?

Because any emission from the seawater below the ice is IR above 5microns at which wavelengths ice is a good absorber whereas seawater is not.

[uniquorn]

Likely that it will freeze top and bottom till it has enough freeboard or area to prevent waves and spray washing over it.

Top freeze can hardly count for more than a few mms if it is based on putative splashes from nearby open water.

A Field and Laboratory Study of Wave Damping by Grease Ice*
Seelye Martin and Peter Kauffman  Journal of Glaciology, Vol. 27, No. 96, 1981
Published online by Cambridge University Press:  20 January 2017
doi:10.3189/S0022143000015392

extract:

In small Arctic leads the grease ice is not herded into Langmuir plumes; rather, as we have observed in many small leads in the Beaufort, Chukchi, and Bering Seas, cold winds cause both the growth of small wind waves and the formation and herding of grease ice to the down-wind end of the lead. Figures 5 and 6 show such a lead near Cape Lisburne on 16 March 1978 at an air temperature of -16 °C and a wind speed of 10 m s^-1. The lead had a wedge shape, about 15 m wide in the cross-wind direction at the boundary between the grease ice and the seawater, and about 50 m long with the apex of the wedge up-wind. Figure 6 shows that the waves which had lengths of 100 mm, abruptly damp out as they enter the grease ice. Also measurements of the grease-ice thickness using the tube technique described earlier showed that the thickness at a distance of 0.1m in in from the leading edge was 80 mm, and in the region behind the wave damping was 50 mm. The photographs also show small pancakes forming on the grease ice similar to those reported in MKW.

my emphasis

Likely that the wave action caused the grease ice to be 30mm thicker before being damped.

[uniquorn]

This may also be of interest:

Frost flowers on young Arctic sea ice: The climatic, chemical, and microbial significance of an emerging ice type
D. G. Barber, J. K. Ehn, M. Pućko, S. Rysgaard, J. W. Deming, J. S. Bowman, T. Papakyriakou, R. J. Galley, D. H. Søgaard
First published: 15 August 2014
https://doi.org/10.1002/2014JD021736

4 Conclusions

The greater presence of young sea ice formations in the Arctic increases both the spatial coverage and the temporal range within which frost flowers occur. At our field site, frost flowers formed when open water became available to a very cold atmosphere and surface wind conditions were low, allowing for the supersaturation of the near-surface boundary layer. The formation of the young ice and its frost flower-covered surface dramatically changed the PAR and the thermal environment of this young OSA interface. A large and contiguous area of frost flowers reduced PAR transmission until it closely resembled a thin snow cover on the sea ice.

Thermally, frost flowers also affected energy exchange across this interface. The frost flowers themselves were 5°C colder than the brine surface, with a temperature gradient that was approximately linear from the base to the upper tip of the frost flowers. Larger (older) flowers, which protruded further into the atmospheric boundary layer, were both colder and lower in brine volume—reaching maximum temperatures that were about 7°C colder than at the base. Our results suggest that expansive frost flower coverage will raise both net longwave and net all-wave radiation. Net radiation and the heat budget will also depend however on associated changes to surface albedo and air-ice sensible heating in the presence of frost flowers. Regarding net radiation, frost flowers will only affect the shortwave budget during a small part of the annual cycle (i.e., when solar insolation is a factor in the surface radiation budget). As sensible heating responds to the air-surface temperature difference, a greater loss of heat is expected for surfaces free of frost flowers during the cold season. A more detailed assessment (beyond the scope of this contribution) of the response of the surface heat budget to frost flowers is underway using these and other data.

my emphasis

[binntho]

Just to make one thing clear: I do no dispute that sea ice in the arctic works as an insulator - that seems to be clear from experience, although the presence of a temperature gradient does NOT prove that ice is a better insulator than the sea water below it.

The question here is whether this insulation property is intrinsic or contingent. And this brings us to the "slow transition" theory which is all about how ice freezes faster when it is thinner. But the start of the discussion was about how there didn't seem to be any evidence for this!

Some interesting theoretical work and other lines of reasoning that others have posted since my original posting seem to indicate that ice does not (necessarily?) freeze faster when thinner. A lot of this discussion was about the insulating effect of ice, and the interesting thing was that many lines of reasoning seem to point to the insulation of sea ice being contingent, not intrinsic.

Now perhaps many people do not understand the words contingent and intrinsic and do not understand what they implicate - so let me try to explain: If ice insulation is contingent on more-or-less random factors such as snow cover and air bubbles, then there is no reason to think that thin ice should freeze faster than thick ice - it all depends.

If, however, ice insulation is intrinsic to the physical properties of ice itself, then insulation very clearly grows with thicker ice IRREGARDLESS of any contingent factors.

Phil above states as fact (without support) that the radiative thermal flux from sea water is blocked by ice. But that is not what I have found in any of the literature I have looked at.

[John_the_Younger]

I recall from way way back (Is there a machine for that, yet?) that igloos use (packed) snow, not "ice" as the snow insulates while ice functionally wouldn't.  A coating of ice would minimize infiltration, but would functionally not add insulation.

I'm appreciating this discussion on ice (from here in Florida).  From the building trade, mass walls and flours can be used to hold heat.  Is this what ice in an ice floe does?

[binntho]

I'm still trying to find time to read the excellent paper that uniquorn posted above, Impacts of snow and surface conditions on radiation fluxes through Arctic sea ice during different seasons

There is a lot of good information there, but my immediate takeaway from page 18 is that rate of increase of albedo of thickening ice doesn't really change after the first 0.8 m, and secondly, that albedo is very heavily dependent on ice cover.

Anyway, uniquorn seems to be somewhat miffed at my claim that freezing from the top due to sea spray is at best minimal and could be described as putative - thought to exist but doesn't really, at least not in any sens of being measurable or of having any impact.

My line of reasoning is the following:

1) Almost all sea ice is so far from open water that there is absolutely no change of spray ever reaching it. The area of ice in contact with open water capable of being sprayed at is at the very maximum around 0.00001% of total area (and yes I did calculate that! - 4 milion square km, half a meter spraying area from the edge).

2) Wind speeds in the artic are generally way below the speed needed to create whitecaps and the consequent wind driven spray on impact, even where ice actually does meet water.

3) Wind- and wave driven compression of slush ice does not mean that it is being covered by spray from above.

[Jim Hunt]

Just to make one thing clear:

But the start of the discussion was about how there didn't seem to be any evidence for this.

There's lots of evidence for that! At the risk of repeating myself:

https://forum.arctic-sea-ice.net/index.php/topic,2709.msg368296.html#msg368296

[binntho]

Just to make one thing clear:

But the start of the discussion was about how there didn't seem to be any evidence for this.

There's lots of evidence for that! At the risk of repeating myself:

https://forum.arctic-sea-ice.net/index.php/topic,2709.msg368296.html#msg368296

I remember that post and thinking "this is another example of the speed of light" - i.e. everything I read went straight through my frontal cortext at 300.000.000 m/s without leaving the slightest trace. I really need some explanation here! And Jim, your style of cryptically understated minimalism, although elegant and amusing, is not good at explaining!

[FredBear]

Thermal radiation is emitted from the surface of a body, any energy below is conducted to the surface layer by conduction or convection. In the polar system ice is fixed and layers of warmer water are usually stratified to reduce mixing. Therefore any thermal radiation is absorbed by the material next to it - a very slow process when tiny temperatures differences try to drive it forward.
Thus conductivity moves the energy in bulk situations towards a cooler state at the surface - where the transparency of the atmosphere allows most of the radiation to escape.
The shorter wavelength energy from the sun can penetrate more ice and water but then heats things up from the inside as well as being absorbed at the surface. The sun represents a small high energy source but the whole sky is a low energy heat sink (with proviso that clouds, etc., can diffuse some energy around, or bounce radiation around.).

[Jim Hunt]

And Jim, your style of cryptically understated minimalism, although elegant and amusing, is not good at explaining!

Sorry for that binntho, but Lady White and I are rather busy at the moment.

Amongst other things we are the proud recipients of a once Great British "no fault" eviction order:

https://www.gov.uk/evicting-tenants/section-21-and-section-8-notices

[Gray-Wolf]

And Jim, your style of cryptically understated minimalism, although elegant and amusing, is not good at explaining!

Sorry for that binntho, but Lady White and I are rather busy at the moment.

Amongst other things we are the proud recipients of a once Great British "no fault" eviction order:

https://www.gov.uk/evicting-tenants/section-21-and-section-8-notices

Bugger!

Best of British with dealing with all that Jim!

[Jim Hunt]

Thanks for your kind words Ian.

Looking on the bright side, at least the new residence is bigger than our current home/office/lab

[uniquorn]

Likely that it will freeze top and bottom till it has enough freeboard or area to prevent waves and spray washing over it.

Top freeze can hardly count for more than a few mms if it is based on putative splashes from nearby open water.

<>
Anyway, uniquorn seems to be somewhat miffed at my claim that freezing from the top due to sea spray is at best minimal and could be described as putative - thought to exist but doesn't really, at least not in any sens of being measurable or of having any impact.
<>

My mistake, I thought we were discussing formation of thin ice.

[P-maker]

Details, details, details...

It comes down to a simple question: If Arctic sea water freezes at -11C, will the increasing cloud cover due to Atlantification prohibit this?

All bids are open. Please don't hesitate to comment. Ice is for everyone to enjoy, as long as it stays solid.

[The Walrus]

Details, details, details...

It comes down to a simple question: If Arctic sea water freezes at -11C, will the increasing cloud cover due to Atlantification prohibit this?

All bids are open. Please don't hesitate to comment. Ice is for everyone to enjoy, as long as it stays solid.

My guess is that it will not prohibit freezing, but slow the process as the cloud cover will moderate temperatures.   On the other hand, it will slow melting as it inhibits solar radiation.  The question is which process will dominate, or will they cancel out.

[Glen Koehler]

Just to make one thing clear: I do no dispute that sea ice in the arctic works as an insulator - that seems to be clear from experience, although the presence of a temperature gradient does NOT prove that ice is a better insulator than the sea water below it.

The question here is whether this insulation property is intrinsic or contingent. And this brings us to the "slow transition" theory which is all about how ice freezes faster when it is thinner. But the start of the discussion was about how there didn't seem to be any evidence for this!

Some interesting theoretical work and other lines of reasoning that others have posted since my original posting seem to indicate that ice does not (necessarily?) freeze faster when thinner. A lot of this discussion was about the insulating effect of ice, and the interesting thing was that many lines of reasoning seem to point to the insulation of sea ice being contingent, not intrinsic.

Now perhaps many people do not understand the words contingent and intrinsic and do not understand what they implicate - so let me try to explain: If ice insulation is contingent on more-or-less random factors such as snow cover and air bubbles, then there is no reason to think that thin ice should freeze faster than thick ice - it all depends.

If, however, ice insulation is intrinsic to the physical properties of ice itself, then insulation very clearly grows with thicker ice IRREGARDLESS of any contingent factors.

Phil above states as fact (without support) that the radiative thermal flux from sea water is blocked by ice. But that is not what I have found in any of the literature I have looked at.

      FWIW from agriculture world.  To protect fruit crops from freezing temperatures growers use the heat of fusion from freezing water applied via irrigation to keep buds from getting below a critical temperature.  But... (here is the relevance to Binntos' quest) ... you have to keep adding new water to freeze, because if you stop too early, ice is a terrible insulator and will do more harm than good by conducting more heat out of buds than if you had not encased them in ice.  (Though heat loss by evaporation from the ice surface has a lot to do with that.)

     In the realm of plant freeze protection, ice being highly conductive of heat energy refers to a thin layer of fresh water around buds, so this example may not be relevant to ASI freeze dynamics.  But in the realm of crop freeze protection, the thermal conductivity of freshwater ice makes it an inherently poor insulator. 

[P-maker]

Walrus,

We are talking physics here. Please come up with one example, where surface temperatures are around -11C when (where) you have a 100% cloud cover (8/8). I doubt you will find many instances, but lets look at the cases to see, if they lend some hope for the future.

[Glen Koehler]

Details, details, details...

It comes down to a simple question: If Arctic sea water freezes at -11C, will the increasing cloud cover due to Atlantification prohibit this?

All bids are open. Please don't hesitate to comment. Ice is for everyone to enjoy, as long as it stays solid.

     

My guess is that it will not prohibit freezing, but slow the process as the cloud cover will moderate temperatures.   On the other hand, it will slow melting as it inhibits solar radiation.  The question is which process will dominate, or will they cancel out.

     Not sure if this is pertinent to Walrus's comment, but for global warming overall, more extensive and/or thicker low cloud cover causes more warming by reflecting back long wavelength radiation at night.  This effect is stronger than the blocking of incoming short-wave radiation during the day.

     But high cirrus clouds composed of ice crystals create net cooling by blocking more incoming solar radiation than any blocking of outgoing long-wave radiation. 

     That is what I understand from work done by Steven Sherwood who seems to be a leading guru for understanding the role of increased cloud cover on the global energy budget.  Cloud responses to warming and cloud effects on warming are areas of active research because they are still poorly quantified in climate models and are thought to have a large influence on Earth system sensitivity to increasing levels of greenhouse gases in the atmosphere.

     James Hansen mentions the need for better understanding of cloud dynamics in his May 18 update (from which the intro and conclusion sections are recommended if you want a quick update on what is happening to your planet, you can skip the gnarly math in the middle). 

     One problem with modeling clouds is that they operate at much finer spatial resolution than global climate models can efficiently process, so clouds are represented as set parameters instead of generated within the model.  As computing resources get better, finer resolution modeling will allow better representation of clouds in both long-term climate models and short-term weather forecast models.

[Glen Koehler]

Walrus,

We are talking physics here. Please come up with one example, where surface temperatures are around -11C when (where) you have a 100% cloud cover (8/8). I doubt you will find many instances, but lets look at the cases to see, if they lend some hope for the future.

     Completely out of my wheelhouse, so I should not say anything, but where is the fun in that?  It seems to me that Arctic temperatures are routinely far below -11C with 100% cloud cover.  It's cold up there!  And frequently overcast.  Instead of -11C with 100% cloud cover being unusually cold, that would be a warm day in the Artic for most of the year.  But if the scope of the question is narrowed to immediately above the surface of open water during melt season, the DMI 80N temperature record indicates -11C is rare to impossible with or without cloud cover.

[The Walrus]

Walrus,

We are talking physics here. Please come up with one example, where surface temperatures are around -11C when (where) you have a 100% cloud cover (8/8). I doubt you will find many instances, but lets look at the cases to see, if they lend some hope for the future.

In Avannaata, Greenland on January 23, 2023 at 10 p.m. it was -22 F (-30 C) and cloudy.

https://www.wunderground.com/history/daily/gl/qaanaaq/BGQQ/date/2023-1-23

On the same day it was snowing in Utqiagvik (Barrow), Alaska while being a rather balmy -7 F (-22 C)

[Phil.]

If, however, ice insulation is intrinsic to the physical properties of ice itself, then insulation very clearly grows with thicker ice IRREGARDLESS of any contingent factors.

Phil above states as fact (without support) that the radiative thermal flux from sea water is blocked by ice. But that is not what I have found in any of the literature I have looked at.

Since you're explaining your use of english you should be aware that it should be REGARDLESS.  :-)

Regarding the different absorption of IR by ice and water try the Introduction to this paper for example: https://royalsocietypublishing.org/doi/10.1098/rsta.2018.0161

[P-maker]

Walrus,

I was not looking at a particular coastal station near the Greenland Ice-sheet. I was hoping for a remote island/floating station in the proper Arctic Ocean. Some borderline cases may appear, but in reality, if you wish to get surface temperatures down to - or close to -11C - you will need clear skies for a number of days over open ocean. I am sorry to say that we are approaching an equitable climate with some speed. Not the best of prospects, but as long as we are ready for it - who cares?

[HapHazard]

Not sure if this is pertinent to Walrus's comment, but for global warming overall, more extensive and/or thicker low cloud cover causes more warming by reflecting back long wavelength radiation at night.  This effect is stronger than the blocking of incoming short-wave radiation during the day.

planet Venus

[kassy]

The question here is whether this insulation property is intrinsic or contingent. And this brings us to the "slow transition" theory which is all about how ice freezes faster when it is thinner. But the start of the discussion was about how there didn't seem to be any evidence for this!

No the transition is slow because before you had a more or less solid thick ice cap everywhere and when you lose that it slows down melt because there is none where this is open water. Then you get the usual refreeze cycle. It produces about the same amount of ice every year in area and extent so far so that is nice as long as it works. Chris expected this to last to about 2025 as quoted above.

If you want to find out why thin ice freezes faster get yourself two earths, on number one we have the old MYI which is much thicker and on number two we have the modern open water version. Now which arctic would freeze more in cms over winter?

Hint: It is the one with open water.

[The Walrus]

Not sure if this is pertinent to Walrus's comment, but for global warming overall, more extensive and/or thicker low cloud cover causes more warming by reflecting back long wavelength radiation at night.  This effect is stronger than the blocking of incoming short-wave radiation during the day.

The warming is occurring predominantly when the sun is not shining; nighttime and winter in the Arctic. The cooler occurs when the sun is shining.  Hence, warmer winters and cooler summers would be expected, with warming in winter being stronger than cooling in summer.

[oren]

Walrus, don't even start this line of argument unless you can show specific global data that shows summers are getting cooler. I will snip otherwise.

[binntho]

The question here is whether this insulation property is intrinsic or contingent. And this brings us to the "slow transition" theory which is all about how ice freezes faster when it is thinner. But the start of the discussion was about how there didn't seem to be any evidence for this!

No the transition is slow because before you had a more or less solid thick ice cap everywhere and when you lose that it slows down melt because there is none where this is open water. Then you get the usual refreeze cycle. It produces about the same amount of ice every year in area and extent so far so that is nice as long as it works. Chris expected this to last to about 2025 as quoted above.

If you want to find out why thin ice freezes faster get yourself two earths, on number one we have the old MYI which is much thicker and on number two we have the modern open water version. Now which arctic would freeze more in cms over winter?

Hint: It is the one with open water.

Can't say I understand much of this. Which is interesting, it sems that the "slow transition" people are not very good at explaining their theory. Hint: perhaps because they don't understand it themselves?

If there is open water, ice forms very quickly until it has capped the water in a few cms - but at that point, if I am understanding FredBear correctly, radiative cooling of the underlying water basically stops. If the ice is solid (clear) it has a very low insulation effect, so conduction of thermal energy from the underlying water will continue, and the ice will thicken from below. Given the low insulation effect, the difference in thickness will probably not create a parabolic change in rate of refreeze after the very first cms.

What really changes the situation is the first snow fall. Now we have insulation - but totally irregardless of thickness! (Yes, Phil, I am one of those irrational and irresponsible abusers of the word irregardless).

This to me sounds contingent. A world with open water at the beginning of  refreeze will see two step changes - the first step change is formation of ice itself, capping the water; the second step is the first snowfall, providing insulation. Nothing here about thickness.

This is as opposed to claims about intrinsic quaility of ice that enables significantly faster refreeze up to a certain thickness (the numbers 0.5m or 0.8m have been bandied about) followed by a much slower rate of freeze.

But what we are most likely seeing is a steady refreeze until the first snowfall. Which implies that it is not "thinner ice freezes faster" but "ice before the first snow freezes faster". Which will appear to be the same thing to a casual observer.

[binntho]

uniquorn, sorry, wee seem to have been talking past each other - not the first time that happens in this forum!

[binntho]

Interesting fact from the SHEBA research: Low clouds increased radiative forcing AT ALL TIMES, also during max insolation. Came as a surprise to me.

Also, maximum radiative forcing occurs at mid-July, some 3-4 weeks after max insolation.

EDIT: Where I live is close to maximum insolation at this time of year (the actual max was a month ago and again after 3 months), but the weather is increasingly cloudy. And the office temperature is markedly higher in cloudy weather than when the skies are clear, which is anectodal evidence that low clouds increase radiative forcing.

[Jim Hunt]

Hint: perhaps because they don't understand it themselves?

Hint: Alternatively?

[binntho]

Hint: perhaps because they don't understand it themselves?

Hint: Alternatively?

Well, that's a given!

[binntho]

Jim Hunt posted in The 2023 melting season thread earlier with a link to a paper that I have been trying my very best to read and understand (linked below).

I have just received a note from Don Perovich (AKA DKP for short):

I agree with your assessment that it does look like the onset of melt. This is a little early, but not incredibly early. Usually bottom melt starts at the very beginning of June. I attached a paper that you might find interesting. The lead author is Cameron Planck, who is now the head of Cryosphere Innovation. ...

From reading this paper, it seems that bottom melt is also to a large degree contingent on nearby open water, rather than on thickness. Bottom melt is strongly related to dispersion, but weakly related to thickness?

If refreeze and melt are both contingent on external factors (snow cover, dispersion), then the whole "slow transition" theory crumbles. Or what?

[oren]

Given the low insulation effect, the difference in thickness will probably not create a parabolic change in rate of refreeze after the very first cms.

It seems this is where we disagree. I believe the rate of thickening does depend on thickness itself -  the thicker the ice, the slower the rate of further thickening, given the same weather.

Also look for the terms Lebedev formula and Stefan formula, I know this was discussed in some threads in the past.

Note: this is indeed the very basis of the "Slow Transition" postulation. If ice grows at the same rate regardless of thickness, there is no compensating factor for the loss of thicker ice, and the Arctic extent/area/volume will crash (should have crashed) by 2016 or whatever.
As it stands, thinner ice and/or open water at the end of the melting season results in a higher growth of ice volume, compared to the past. Therefore, despite the low volume at the end of the melting season, the end of the freezing season sees a lower decline in volume, preventing or delaying the inevitable crash.

Some images off the web, and a hastily produced chart of volume behavior over time:

[The Walrus]

Walrus, don't even start this line of argument unless you can show specific global data that shows summers are getting cooler. I will snip otherwise.

Sorry, I thought the cloud effect in the summer was common knowledge.

https://acp.copernicus.org/articles/23/2579/2023/