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binntho

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Re: Basic questions and discussions about melting physics
« Reply #150 on: June 15, 2020, 04:42:35 AM »
very interesting!
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Tor Bejnar

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Re: Basic questions and discussions about melting physics
« Reply #151 on: June 15, 2020, 06:17:30 PM »
Indeed!  While the graphs are 'above my pay grade', the explanations were fully within my grasp.
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Freegrass

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Re: Basic questions and discussions about melting physics
« Reply #152 on: June 17, 2020, 08:41:15 AM »
It would be great to get an answer from somebody who studies this stuff.
I agree, but it looks like nobody is home today...  :(
Is anyone seeing this?

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Human Habitat Index

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Re: Basic questions and discussions about melting physics
« Reply #153 on: June 17, 2020, 08:59:49 AM »
Anecdotally we have had clear unusually chilly nights in southern Australia, consistent with the effect of less aerosols in the atmosphere.
There is a principle which is a bar against all information, which cannot fail to keep a man in everlasting ignorance. That principle is contempt prior to investigation. - Herbert Spencer

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Re: The 2020 melting season
« Reply #154 on: July 07, 2020, 09:13:36 AM »

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

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

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

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




pleun

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Re: Re: The 2020 melting season
« Reply #155 on: July 07, 2020, 09:18:24 AM »

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

Yet the temperature just above the icecubes will be the same in both cases. You just took down your own argument...

El Cid

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Re: Re: The 2020 melting season
« Reply #156 on: July 07, 2020, 09:24:39 AM »
Take two full and frozen ice cube trays out of your freezer. Put one in your refrigerator which might be cooled to 5C and shut the door so its dark inside.

And now take that ice cube and put it out into the full sun. See what happens. And how fast

oren

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Re: Basic questions and discussions about melting physics
« Reply #157 on: July 07, 2020, 01:33:08 PM »
To whom it may concern, let it be known. A large region of sea ice will keep surface air temperatures pegged near the melting point, due to the energy soaked up by the phase change of ice into water. Thus surface air temperatures are often not very informative during the Arctic summer.

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Re: Basic questions and discussions about melting physics
« Reply #158 on: July 07, 2020, 02:05:09 PM »
To whom it may concern, let it be known. A large region of sea ice will keep surface air temperatures pegged near the melting point, due to the energy soaked up by the phase change of ice into water. Thus surface air temperatures are often not very informative during the Arctic summer.

These anomaly graphs http://ocean.dmi.dk/arctic/meant80n_anomaly.uk.php clearly show how Arctic temps have climbed in autumn, winter and spring but have been flat as a pancake in summer.

Phoenix

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Re: The 2020 melting season
« Reply #159 on: July 07, 2020, 05:24:49 PM »

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics -

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

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

sedziobs

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Re: Re: The 2020 melting season
« Reply #160 on: July 07, 2020, 05:33:29 PM »
Attached is the latest DMI 80N temperature chart.
This chart tells us next to nothing about energy transfer to ice, especially under high pressure.

igs

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Re: Re: The 2020 melting season
« Reply #161 on: July 07, 2020, 06:30:56 PM »

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics -

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

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

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

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

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

Also i think i remember there is a DMI above 80N thread somewhere, just in case you're interested to find info WHY it is as it is  ;)

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Re: Re: The 2020 melting season
« Reply #162 on: July 07, 2020, 06:54:37 PM »

The surface temperature of melting ice is always going to be zero until the ice has melted and turned into water - that's thermodynamics -

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

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

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

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

Stop attempting to derail constructive conversation because you are bored at home during Covid or whatever your affliction is.
« Last Edit: July 07, 2020, 07:00:22 PM by Viggy »

jens

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Re: Basic questions and discussions about melting physics
« Reply #163 on: July 14, 2020, 09:36:20 AM »
I have no idea into which topic to post this, but in some topics (forgot which one) there was discussion about how strongly preceding winter influences the melting season. It looks like it has most influence on the early season melting, with gradually diminishing effect during the year. There was one chart which showed that temperature-wise 2016 had the warmest winter and subsequently 2016 has been duly leading in May and June. However, it lost its advantages, when the effects of summer weather have kicked in.

oren

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Re: Basic questions and discussions about melting physics
« Reply #164 on: July 14, 2020, 01:27:56 PM »
A really good (cold, little export) winter can give extra ice, and of course the opposite is true for a bad winter. OTOH a really bad summer (warm, sunshine, export) can take away extra ice and cause deficit, while a good summer will do the opposite. Which one of these wins over the other depends on the magnitude, so there can be no definitive answer.
What has already been proven is that a very cold or warm winter is no guarantee of the summer minimum - 2012 had high volume in March, while 2017 had the lowest volume ever. But at the end of summer their roles were reversed.

Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #165 on: July 21, 2020, 05:04:22 AM »
     Does anybody care to disabuse me of my conjecture that there is a nonlinear relationship between ice thickness and melt resistance - with decrease in melt resistance curving down faster than the linear % decline in thickness - due to qualitative differences in thinner vs. thicker ice?

     The fact that ice accumulation is radically nonlinear with increasing thickness is accepted as established fact, e.g. the curve published by Thorndike 1975
.

     Earlier this year I pitched the idea that the reverse is true for melting, with 1 meter thick ice melting at twice the rate of 2 meter ice (0.8 cm/day vs. 0.4 in the example shown):  .

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

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

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

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

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

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

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

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

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

    One more conjecture.  I think that as the average thickness in the High Arctic Seas, as shown in gerontocrat's graph, is approaching 1 meter in September, the accelerated thin ice melt effect, which might have been relatively inconsequential until now, will become an increasingly important influence.  As a result, there will be "Extent goes poof" events of increasing scale and frequency over the next 10 years, resulting in a BOE by the early 2030s if not before.
« Last Edit: July 21, 2020, 07:40:08 AM by Glen Koehler »

Steven

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Re: Basic questions and discussions about melting physics
« Reply #166 on: July 21, 2020, 12:09:24 PM »
average thickness chart posted by gerontocrat at https://forum.arctic-sea-ice.net/index.php/topic,119.msg275579.html#msg275579  (A chart which I nominate for the ASI Graphical Hall of Fame).

Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.

gerontocrat

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Re: Basic questions and discussions about melting physics
« Reply #167 on: July 21, 2020, 01:59:18 PM »
Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.
I have understood that area data was badly affected by melt ponds when insolation was high in early to mid-summer, and that produced the underestimates. But I also thought I had read that this effect diminished in the late Arctic summer, (starting around now) by which time melt ponds had drained, and as insolation quickly reduced in the high Arctic, melt ponds would no longer form to any great extent. So I always thought that by the minimum, the area data was less out of wack.

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

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

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

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

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Re: Basic questions and discussions about melting physics
« Reply #168 on: July 21, 2020, 07:01:26 PM »
Glen,
Sea ice in the early part of the melting season melts more slowly than in the late part of the melting season because the ice is colder to start with, and it takes time for the ice in the middle (core) - between sea water and air - to warm.  Even after the ice surfaces start melting, 'heat' applied to the ice is partially directed to the core.  I've seen charts showing this phenomenon on these threads, but I don't recall where.

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

Anyway, this is a little part of the answer.
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Steven

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Re: Basic questions and discussions about melting physics
« Reply #169 on: July 21, 2020, 08:34:55 PM »
Take that graph with a grain of salt.  Thickness should not be calculated by dividing volume by NSIDC area.  It is known that NSIDC area substantially underestimates the real sea ice area, by about 10 to 25% in September.  So the "thickness" in that graph is an overestimate.

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

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

If you had bothered to compare your thickness graph with the official PIOMAS thickness graph, you would have noticed that your numbers are systematically too high during Summer and Autumn, by about the percentages I posted.  Even as late as November there is still a discrepancy.

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

NSIDC area is useful for making predictions about the minimum (Slater, Dekker, Tealight etc).  But if you want to know the real sea ice area, you're better off using the Hamburg AMSR2 sea ice area.  It's available on Wipneus' site.

NSIDC area underestimates the real sea ice area, not only in Summer but also in Autumn.  This was discussed several times in the Home Brew thread.  Last year I posted some graphs about this: see here.  Below is a similar graph, showing the ratio of NSIDC and AMSR2 area, averaged over the past 7 years.  Looking at individual years, the daily ratio in September ranges between 0.76 and 0.91.



grixm

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Re: Basic questions and discussions about melting physics
« Reply #170 on: July 21, 2020, 08:53:41 PM »
Has anyone combined the PIMOAS thickness data with AMSR2 area to create a better volume measurement then?

oren

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Re: Basic questions and discussions about melting physics
« Reply #171 on: July 21, 2020, 09:25:00 PM »
Grixm - I have done it for the CAB and the ESS and posted some charts in the past in the PIOMAS thread. The data is somewhat problematic. I will make a similar chart for the whole Arctic and post it later tonight.

Steven - thanks for the very informative post.

gerontocrat

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Re: Basic questions and discussions about melting physics
« Reply #172 on: July 21, 2020, 09:48:25 PM »
Re Steven's critique...

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

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

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

Do I accept that going back to 1979 for thickness graphs is just not possible? Oren has got since 2013 sorted, so if the answer is yes, time to dump my thickness graphs into the gigo bucket 
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oren

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Re: Basic questions and discussions about melting physics
« Reply #173 on: July 21, 2020, 10:27:16 PM »
Don't dump them Gero. Maybe they don't represent actual accurate thickness, but they are still informative and enable a sort of comparison between years going back much longer.

ajouis

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Re: Basic questions and discussions about melting physics
« Reply #174 on: July 21, 2020, 10:47:05 PM »
Gerontocrat I wholly agree with Oren, even if it is not perfect, more data is better than less data, especially as it helps with longterm trends, plus who knows maybe your modelisation is good enough to be picked up by the (rest of the) scientific community and will become a new standard, who knows.
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Re: Basic questions and discussions about melting physics
« Reply #175 on: July 23, 2020, 12:14:31 AM »
This data from 21st of July 2019 from gerontocrat was within 20,000 km^2 off the September minimum very accurate.

« Last Edit: July 23, 2020, 12:19:34 AM by glennbuck »

Tor Bejnar

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Re: Basic questions and discussions about melting physics
« Reply #176 on: July 23, 2020, 01:44:07 AM »
There has been a great deal of discussion recently about discerning/calculating ice thickness and very little discussion about melting physics.  There must be a relation between the two topics, but don't ask me to explain it!  :-\
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binntho

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Re: Basic questions and discussions about melting physics
« Reply #177 on: July 23, 2020, 07:24:55 AM »
I think we all agree, as Glen points out, that the decline in extent must at some point catch up with the decline in volume. Hence the decline in extent cannot continue at its current linear rate. But will the rate of change be incremental or sudden? I.e. will the curve bend or break?

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

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

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

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

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

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

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

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

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

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

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

But for the future, in my opininon the main factor in increasing the rate of melt will be the amount of open water in the second (post max insolation) part of the melting season. A steady linear decline overall will secure the increased amount of open water up to that point, and a non-linear effect of open water + storminess will take care of the rest.
« Last Edit: July 23, 2020, 08:23:15 AM by binntho »
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oren

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Re: Basic questions and discussions about melting physics
« Reply #178 on: July 23, 2020, 08:20:08 AM »
Welcome back binntho. Excellent post.

Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #179 on: July 23, 2020, 06:53:18 PM »
Welcome back binntho. Excellent post.
+1 :)

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Re: Basic questions and discussions about melting physics
« Reply #180 on: July 23, 2020, 07:30:54 PM »
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 

Also, the physics is reversible.  If the ice were to thicken, it would return to its previous state.

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Re: Basic questions and discussions about melting physics
« Reply #181 on: July 23, 2020, 07:57:54 PM »
Question about draining of melt ponds.

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

Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #182 on: July 23, 2020, 08:00:25 PM »
     The only way for Volume loss trend to decline relative to Extent is for Thickness to increase.  With the net energy balance of the Arctic system already above equilibrium to maintain the current seasonal ice levels, compounded by increasing energy inputs from GHG emissions that not only continue to load the system, but still doing so at any increasing rate, I see virtually no chance for Thickness levels to increase, or for the Volume rate of decline to lessen.

BeeKnees

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Re: Basic questions and discussions about melting physics
« Reply #183 on: July 23, 2020, 08:23:51 PM »
Maybe the wrong place but I'm sure it will be moved or deleted .

Interesting little scripps video simulating how icebergs melt

https://www.youtube.com/watch?v=8YC779XMvgk&feature=youtu.be

The Walrus

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Re: Basic questions and discussions about melting physics
« Reply #184 on: July 23, 2020, 08:39:03 PM »
     The only way for Volume loss trend to decline relative to Extent is for Thickness to increase.  With the net energy balance of the Arctic system already above equilibrium to maintain the current seasonal ice levels, compounded by increasing energy inputs from GHG emissions that not only continue to load the system, but still doing so at any increasing rate, I see virtually no chance for Thickness levels to increase, or for the Volume rate of decline to lessen.

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

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/

sedziobs

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Re: Basic questions and discussions about melting physics
« Reply #185 on: July 23, 2020, 10:00:39 PM »
Question about draining of melt ponds.

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

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

Below is Jim Hunt's chart of the temperature profile for a buoy (the x-axis is vertical position from the top in 2cm increments).
 


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

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

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

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

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

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

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

More information can be found in the buoys thread

Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #186 on: July 23, 2020, 10:11:52 PM »
Not at all.  We are talking about a trend line, not an absolute value.  The volume trend line has already lessened over the past several years.
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
    I see nothing in the link to PIOMAS update about the trend line slope for Volume becoming less negative.  What it does say is "Sea ice volume is an important climate indicator. It depends on both ice thickness and extent."  In order for Volume trend to change, antecedent values in Thickness and/or Extent must change in the same direction.

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

    You are free to consider the Extent linear trend estimate (2072) instead of the Volume linear trend estimate (2032) as the better estimator for when September ASI for both measures will approach zero  (see https://forum.arctic-sea-ice.net/index.php/topic,2348.msg273488.html#msg273488).  But you won't have much company in thinking that.
 
     As much as I can guarantee anything, I guarantee you that the date for Extent going below 1M km2 is better predicted by the Volume trend line on Wipneus chart as 2030 =+/- 6 years,
« Last Edit: July 24, 2020, 04:41:01 PM by Glen Koehler »

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Re: Basic questions and discussions about melting physics
« Reply #187 on: July 23, 2020, 11:22:23 PM »
sedziobs

But why would it drain if the bottom is below sea level? Even if there is different density between the water in the pond and the water in the surrounding ocean, there would still be water left in the pond.
« Last Edit: July 23, 2020, 11:36:21 PM by mdoliner »

sedziobs

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Re: Basic questions and discussions about melting physics
« Reply #188 on: July 23, 2020, 11:58:36 PM »
sedziobs

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

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

This is just what I have learned reading the forum over the years. I'm no expert by any means.

Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #189 on: July 24, 2020, 02:24:43 AM »
     Summary of the Thin ice accleration hypothesis -- Absent some qualitative effect that makes thinner ice HARDER to melt (which does not seem to be the case at all), even without any effect of qualitative differences for thinner ice that reduce melt resistance, it seems irrefutable that 1M km2 of 1-meter thick ice (thus 1M CUBIC meters of ice) will melt out faster than 1M km2 of 2-meter thick ice (2M cubic meters) simply because there is only half as much ice to melt. 

    As Thickness declines and approaches 1 meter in late summer (and as average albedo declines with Extent losses) the rate of Extent losses will likely increase between now and 2030.  I don't even want to be right about this, because it is kind of sickening to think about the consequences.  But my rational mind also wanted an explanation for how the Extent and Volume trends will, as they arithmetically must, meet by the time September ice approaches extinction.

binntho

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Re: Basic questions and discussions about melting physics
« Reply #190 on: July 24, 2020, 06:09:44 AM »
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 
Overreach indeed, you should never say never (or "everyone agrees" because there is always someone ...)

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

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

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Re: Basic questions and discussions about melting physics
« Reply #191 on: July 24, 2020, 02:47:22 PM »
Not at all.  We are talking about a trend line, not an absolute value.  The volume trend line has already lessened over the past several years.
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
    I see nothing in the link to PIOMAS update about the trend line slope for Volume becoming less negative.  What it does say is "Sea ice volume is an important climate indicator. It depends on both ice thickness and extent."  In order for Volume trend to change, antecedent values in Thickness and/or Extent must change in the same direction.

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

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

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

https://forum.arctic-sea-ice.net/index.php/topic,2348.msg276462.html#msg276462

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Re: Basic questions and discussions about melting physics
« Reply #192 on: July 24, 2020, 03:23:32 PM »
I think we all agree that extent and volume must converge.  However, I think binntho has overreached, claiming everyone agree that extent must "catch up" to volume.  It is plausible that volume will slow down to match extent. 
Overreach indeed, you should never say never (or "everyone agrees" because there is always someone ...)

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

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

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

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

binntho

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Re: Basic questions and discussions about melting physics
« Reply #193 on: July 25, 2020, 08:05:55 AM »
I think it is less of either/or than both converging together.  In that case, extent would decrease faster, while volume decreases slower, merging when the ice disappears.  Note that thickness is decreasing at a rate in between volume and extent (roughly halfway according to Stephan's table).  Mathematically, this ensures that volume would decrease faster (initially) than extent as the added dimension (thickness) is decreasing also.  If thickness were held constant, volume and extent would decrease at the same rate.  As I pointed out to Glen, the slope of the volume decrease has lessened over the past decade, indicating that volume is decreasing at a slower rate.

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

Besides, the mathematics of the case are not important. This is a physical system, highly complex and variable. And I disagree that there is any indication of the slope of the volume decrease slowing down over the last decade. The variability is too great to allow any such conclusion. The image below, from Stephen's post gives me absolutely no indication of a slowdown.

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

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

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

The apparent "slowdown" that you think you see in the last decade is not statistically valid - but the large fluctuation is interesting, and could perhaps be indicative of a stalled acceleration. In other words, the system could be trying to accelerate melt after 2010 but a temporary stall in the middle of the decade confuses the picture.
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wdmn

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Re: Basic questions and discussions about melting physics
« Reply #194 on: August 12, 2020, 06:07:20 PM »
I'm trying to conceptualize a seemingly simple problem about freezing physics. My goal is to determine air temperatures at which ice forms rapidly on the surface (assuming no waves/little wind). After some thought I have decided I have to first think in terms of melting physics.

If we have the enthalpy of fusion for ice at:

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

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

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

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

Any general advice to sort out my thinking would be much appreciated.

blumenkraft

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Re: Basic questions and discussions about melting physics
« Reply #195 on: August 12, 2020, 06:11:15 PM »
Wdmn, the phase change itself needs energy.

Have you considered this?

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


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Re: Basic questions and discussions about melting physics
« Reply #196 on: August 12, 2020, 06:14:18 PM »
Thanks Blumenkraft,

I have seen that graph. I'm just wondering how to start thinking about kJ/kg in terms of temperature that is not instantaneous (I assume all of those kJ need not be available at the same instant in order for melt to occur, since it occurs over time)...

Tor Bejnar

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Re: Basic questions and discussions about melting physics
« Reply #197 on: August 12, 2020, 07:55:08 PM »
The 'rule of thumb' is that Arctic sea water generally starts actually freezing when the air temperature gets down to -10C.  The reasoning behind this, I recall (I'm not a physicist) is that sea water cooled at the surface sinks and is replaced by the warmer water from just below.  Actual freezing starts when the rate of heat exchange at the surface overtakes the rate of vertical water circulation.

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

But I cannot help with the equations to express this!
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Glen Koehler

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Re: Basic questions and discussions about melting physics
« Reply #198 on: August 19, 2020, 08:07:28 PM »
From https://nsidc.org/arcticseaicenews/2020/8/
  NSIDC update August 18 2020

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

      I suspect that relationship will be a key factor resulting in accelerated melt rates in coming years.  It would be very interesting to see a chart that helps quantify the influence of thickness on ice melt rate.  Surely such a chart must exist somewhere, but I have not seen it.  If anyone has an image or link please post it.  Thanks in advance for anyone who can do so.

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Re: Basic questions and discussions about melting physics
« Reply #199 on: August 19, 2020, 09:16:01 PM »
The 'rule of thumb' is that Arctic sea water generally starts actually freezing when the air temperature gets down to -10C.  The reasoning behind this, I recall (I'm not a physicist) is that sea water cooled at the surface sinks and is replaced by the warmer water from just below.  Actual freezing starts when the rate of heat exchange at the surface overtakes the rate of vertical water circulation.

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

But I cannot help with the equations to express this!
After an extended discussion in one of the previous melt years I think the consensus was this rule of thumb was true for a specific region. If a region still has ice at the start of the melt season it can freeze at higher temperatures.