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oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3500 on: August 15, 2020, 09:53:13 AM »
I think it's pretty clear grixm. Extent would be shown as fully ice-covered, but ice concentration data would show less than 100% because of surface wetness and a bit of open water in parts of the pixel. The signal would be different and the algorithm used for concentration data will be able to judge lower concentration and thus lower area in that pixel.
Basically, what you said.

grixm

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3501 on: August 15, 2020, 10:50:07 AM »
I think it's pretty clear grixm. Extent would be shown as fully ice-covered, but ice concentration data would show less than 100% because of surface wetness and a bit of open water in parts of the pixel. The signal would be different and the algorithm used for concentration data will be able to judge lower concentration and thus lower area in that pixel.
Basically, what you said.

Thanks, that's what I thought

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3502 on: August 16, 2020, 11:52:39 AM »
[size=0px]https://nsidc.org/data/nsidc-0051Parameter Description[/size]Sea ice concentration represents an areal coverage of sea ice. For a given grid cell, the parameter provides an estimate of the fractional amount of sea ice covering that cell, with the remainder of the area consisting of open ocean. Land areas are coded with a land mask value.[/size][size=0px]
[/size]From NSIDC[/font]

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3503 on: August 17, 2020, 11:17:04 AM »
Does anyone know what is going with Greenland melt ponds? It looks to me like they have melted all the way through the ice sheet but that seems unlikely. Am I missing something? Is it some weird reflection thing? Is it normal?

binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3504 on: August 17, 2020, 11:25:54 AM »
Does anyone know what is going with Greenland melt ponds? It looks to me like they have melted all the way through the ice sheet but that seems unlikely. Am I missing something? Is it some weird reflection thing? Is it normal?
It certainly looks as if you can see right through the ice sheet!

But I think these are wind-driven artifacts, i.e. loose ice crystals are driven by wind from the upper left, and deposited in bands on the pond surface. They then drift down to the right as they meilt.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3505 on: August 17, 2020, 11:27:09 AM »
Does anyone know what is going with Greenland melt ponds? It looks to me like they have melted all the way through the ice sheet but that seems unlikely. Am I missing something? Is it some weird reflection thing? Is it normal?

Some of the melt ponds do drain down through the ice sheet. These are called moulins. They don't always reach the base of the ice sheet, but they can. In fact, it's thought that the draining of lakes (formation of a moulin) can speed up the ice movement by lubricating the base of the ice sheet with water!
I recently joined the twitter thing, where I post more analysis, pics and animations: @Icy_Samuel

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3506 on: August 17, 2020, 03:07:24 PM »
Thanks I wasn't sure if it was some sort of illusion or not. A dozen or so moulins have formed near Jakobshvan glacier. Some appear to be nearly a kilometer wide. That seems especially large compared to the video. The images are from Sentinel. Are these new or are they just hidden most of the year?
« Last Edit: August 17, 2020, 03:14:53 PM by interstitial »

binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3507 on: August 18, 2020, 06:50:29 AM »
Thanks I wasn't sure if it was some sort of illusion or not.
It was a sort of illusion - the bands of melting wind-driven ice on the surface of the pond gives the illusion of looking down a deep hole.

A dozen or so moulins have formed near Jakobshvan glacier. Some appear to be nearlya kilometer wide. That seems especially large compared to the video. The images are from Sentinel. Are these new or are they just hidden most of the year?
You are seeing melt ponds, not moulins. A moulin is a hole in the glacier, and they are small, at most very few meters across. I doubt very much if you can see moulins in aerial photography, and definitely not from a satellite, althoug moulins can be inferred when a pond drains from one day to anouther.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3508 on: August 20, 2020, 11:37:44 AM »
I understand that the Sea Ice Extent is based on a there being 15% or less ice per square kilometer. This is a very conservative figure and I believe under estimates how low the Sea Ice Extents actually are.  Has anyone actually worked out the Extent using a higher figure, EG 30 or 40% ?

Tor Bejnar

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3509 on: August 20, 2020, 05:05:03 PM »
I think you meant, "Sea Ice Extent is based on a there being 15% or less more ice per square kilometer grid unit."
Different organizations have significantly different grid units.  (JAXA uses a finer grid than does NSIDC, but I don't pay much attention to these details and don't know how to put my hand on them quickly.)  I recall someone 'playing around with' different thresholds (the "15%") last year or before, but don't recall their conclusions.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3510 on: August 20, 2020, 07:04:29 PM »
Their conclusion was it didn't seem to make much difference raising the 15 % cutoff threshold decreased the amount of ice counted however the same basic trends were produced. It might change relative positions of years on a given date but overall the positions for the most part didn't move more than a few places. I prefer to include as much ice as possible so drop the cutoff to 0% ice.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3511 on: August 20, 2020, 07:33:29 PM »
I understand that the Sea Ice Extent is based on a there being 15% or less ice per square kilometer. This is a very conservative figure and I believe under estimates how low the Sea Ice Extents actually are.  Has anyone actually worked out the Extent using a higher figure, EG 30 or 40% ?

Yes, i brought up the exact same thought some time ago and several times and some tried to calculate it while the results were not convincing and therefore i kept my/your opinion but didn't bring it up further.

This year, right now, this could play exactly a big role, because if large parts of the reminder are on the verge to drop below 15% over a period of 2-4 days we shall have a shocker coming.

Basically it calculations can only verify, the entire thing is logical and as far as I remember the other numbers like 20% and 30% are not readily and reliably available, they are modeled at best and some guessed.
« Last Edit: August 20, 2020, 07:52:39 PM by igs »

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3512 on: August 21, 2020, 12:13:21 PM »
NSIDC uses a 25x25 km2 grid. JAXA uses 10km, so does Bremen, Uni Hamburg uses 3.125 km, and the new product from AWI that is replacing UHH is using 6.5(??) km or some other number higher than 3.125.

I think what really matters is area, not extent, so all this threshold thing doesn't matter much. Extent is an old approximation of area from the days when measurements were crude and ice was contiguous. Area still suffers from measurement problems during the summer, but at min ice surface is mostly frozen.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3513 on: August 21, 2020, 04:22:29 PM »

I think what really matters is area, not extent, so all this threshold thing doesn't matter much. Extent is an old approximation of area from the days when measurements were crude and ice was contiguous. Area still suffers from measurement problems during the summer, but at min ice surface is mostly frozen.


Absolutely, especially in 1-2 weeks when the CAB will be overfrozen again on the surface and area measurements become more reliable/accurate again.
« Last Edit: August 21, 2020, 05:37:15 PM by igs »

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3514 on: August 21, 2020, 05:31:23 PM »
Congrats on your 2000 likes oren. You've won a two week vacation in Israel 10000ya :).
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3515 on: August 21, 2020, 06:29:45 PM »
NSIDC uses a 25x25 km2 grid. JAXA uses 10km, so does Bremen, Uni Hamburg uses 3.125 km, and the new product from AWI that is replacing UHH is using 6.5(??) km or some other number higher than 3.125.

I think what really matters is area, not extent, so all this threshold thing doesn't matter much. Extent is an old approximation of area from the days when measurements were crude and ice was contiguous. Area still suffers from measurement problems during the summer, but at min ice surface is mostly frozen.

NSIDC also has two MASIE products 4 km and 1 km They use any data they can get and some manual evaluation is done so they are not considered comparable but given the ways the arctic is changing I suspect they are more comparable. That is my personal opinion and one not shared by most people including those who produce MASIE.  I am excited for the new AWI product.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3516 on: August 21, 2020, 11:21:09 PM »
I understand that the Sea Ice Extent is based on a there being 15% or less ice per square kilometer. This is a very conservative figure and I believe under estimates how low the Sea Ice Extents actually are.  Has anyone actually worked out the Extent using a higher figure, EG 30 or 40% ?

The graph below shows the NSIDC daily sea ice extent for yesterday (20th August) for the years 2005-2020 using 3 different threshold values to define extent  (blue: 15% concentration, red: 30%, green: 45%).



oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3517 on: August 22, 2020, 02:11:14 AM »
Thanks nanning, though the prize is somewhat dubious...

Interstitial, I wish a multi-sensor product like MASIE could be produced with a repeatable automated algorithm that enables cocnsistent comparisons.
For example, combining AMSR2 with Worldview.

A-Team

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3518 on: August 22, 2020, 01:23:46 PM »
Quote
Oren: the new product from AWI that is replacing UHH is using 6.5(??) km or some other number higher than 3.125.
That's correct. The new AMSR2_AWi product has a resolution of 5.0 km that's intermediate to the two previous AMSR2_UHH products of 3.215 and 6.25. All these were developed by Lars Kaleschke and colleagues. The gif below simulates grid coverage (pixel footprints) of the north pole melt ponds -- the grid we get vs the grid we need.

For a fuller explanation, see:
https://forum.arctic-sea-ice.net/index.php/topic,382.msg282674.html#msg282674
« Last Edit: August 22, 2020, 02:08:50 PM by A-Team »

colding

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3519 on: August 22, 2020, 01:29:59 PM »
Hi,

Apologies if this stupid question has been asked and answered before, but from time to time I read the assumption, that a low minimum of summer sea ice leads to a lot of heat being radiated from the sea in winter, thus leading to a "recovery" year the next summer. The assumption is that the ocean loses so much heat in winter, that sea ice melt is affected the next summer.

However, I've not seen anyone substantiate that claim. Is the ocean really physically able to lose a significant fraction of its heat content during the winter? There's a lot of heat in the arctic water column and my gut feeling is that the heat lost during winter is really rather insignificant in comparison, even if we start from a BOE.

Naturally, a strong halocline and very little mixing will give a very cold upper layer, but since most of the ice still melts out in the summer, there must still be some significant mixing going on, even in ice covered waters, replacing the heat lost in winter to radiation.

Long story short: I would assume that any heat lost from open waters to radiation in winter, is insignificant compared to the total energy content of the arctic ocean and easily replaced from deeper water due to mixing. Any "recovery" seen the next year is, in my mind, therefore more likely caused by weather than due to this lost heat.

Am I totally wrong?

Thanks :-)


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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3520 on: August 22, 2020, 01:51:43 PM »
Colding, did you see vox's interesting post #539 on the What's New thread?:
https://forum.arctic-sea-ice.net/index.php/topic,596.msg282610.html#new

While it does not answer your question directly, it certainly provides evidence that stored heat in the arctic is becoming increasingly available to hinder winter freeze up. As for your question, my guess is that in the traditionally strongly stratified arctic, winter heat loss to space is significant in the dynamics of seasonal freeze/thaw, but that the quantity of deep heat was always there and enormous. But now, that setup is beginning to fail due to enhanced mixing.

The Walrus

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3521 on: August 22, 2020, 02:01:48 PM »
You are not totally wrong.  Open water loses heat at night.  Once we pass the autumnal equinox, the hours of darkness exceed those of light, and nighttime losses exceed daytime gains.  This is why the minimum occurs at this time.  As the season progresses, heat losses increase from the ocean as sunlight decreases.  The more open water, the greater the heat losses.  Ice formation reduces the heat loss.  Whether or not this leads to a recovering the next winter has not been established.  The heat loss is not insignificant.  This has led some to speculate that an Arctic BOE is further into the future than many speculate.  Even mixing of warmer waters will not prevent freezing during the long, cold Arctic nights.  The heat lust is proportional to the temperature difference between the air and water.

Let It Go

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3522 on: August 22, 2020, 04:15:41 PM »
A big event that happened this year in the Arctic was the breaking of the Milne Ice Shelf as mentioned on this forum at the beginning of this Month. And a week later in the mainstream-media (thank God for this Forum), there it was also mentioned that this was the last intact ice shelf.
From a Wikipedia search, i learned that the only other ice-shelves not attached to Greenland or Antarctica are attached to Ellesmere Island and Russia. But little can be found about these Ice shelves (especially from the Russian Ice shelves) except when one has broken up. Does anybody have a list of all the remaining Ice shelves attached to Ellesmere Island or Russia with their respective sizes?

https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=3017.0;attach=281944;image
Also What is this ice in the northeast of this picture. It looks like the calving of an Ice Shelf, as this part is attached to ice that remains in its place and doesn't drift away, although it probably isn't, considering it didnt gain any attention.

In the topic about the Vavilov Ice Cap (https://forum.arctic-sea-ice.net/index.php/topic,3214.0.html) we see that the ice cap is flowing at record speed into the ocean. Can this ice be considered a new ice shelf?

From doing a little more research, i think the ice in the first picture is probably fast ice, although now i don't understand what the difference is between fast ice and ice shelves.



P.S.: Considering this is already a long post, let me make it longer by saying i just recently realised a lot of the forum members who post a lot are actual scientists and doing their PhD's and stuff in fields related to the arctic. As someone who has no scientific background in one of these fields whatsoever i just want to thank you all for sharing your knowledge on this site. It is much appreciated.
« Last Edit: August 22, 2020, 04:22:22 PM by Let It Go »

HapHazard

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3523 on: August 22, 2020, 08:40:01 PM »
Is the ocean really physically able to lose a significant fraction of its heat content during the winter?
IIRC, one part of that equation is ice cover. Heat loss would be much higher when it's open water, and that rate drops substantially as soon as the surface freezes over.

Hopefully someone can correct me or explain it better. Because, honestly, my memory sucks!  >:(

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3524 on: August 22, 2020, 08:47:49 PM »
Yes I do too but the inconsistency of MASIE is probably overstated. It is mostly a repeatable automated algorithm it is just a person looks at that data and if they get some anomalous data they may make some manual corrections. Consistency is desirable mostly because it is an indicator of accuracy. Consistency of method is a useful way to judge how accurate comparisons are. They state the manual corrections are minor and specific to region and short time spans. The bigger issue is how consistent data is when they introduce new sensors and refine the algorithm to current conditions.  Compare this to long term data.

Unless your model includes every subatomic particle from the big bang to now there are external factors which it is assumed have no to minimal effect on your system. In essence they can be ignored. If the external factor is important a good model at the very least allows it to be considered as an external forcing. Preferably it can be included. If the model works good for a while and then fails there is an factor not previously considered. An algorithm works the same way.
The algorithms for long term Ice area and extent have known flaws. Extent works fine when ice is thicker but as the ice has thinned it has become less indicative of the state of the Ice. At one time the only thin ice was near the edge this kept errors of thin ice to a small portion of the total.  Area is only partial correction for that it does reduce for gaps in the ice but it also runs into the problems of melt ponds. With a greater fraction of thin ice to thick ice the error increases and accuracy drops.
There is some question as to how consistent the long term record is given the overlap of sensors was too short to fully validate some of the transitions. The efforts for consistency further decrease overall accuracy especially of the later data.   
My main point is the loss of accuracy over the 40+ years of algorithms likely exceeds the lack of consistency of MASIE data over its 14 year span. Long term extent data may grab headlines but is also becoming less relevant as an indicator of ice condition in the Arctic. The dismissive attitude of the more accurate number is disappointing

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3525 on: August 22, 2020, 08:53:39 PM »
Quote
from time to time I read the assumption, that a low minimum of summer sea ice leads to a lot of heat being radiated from the sea in winter, thus leading to a "recovery" year the next summer. The assumption is that the ocean loses so much heat in winter, that sea ice melt is affected the next summer.
Colding, let's separate two issues here:
* In order to freeze the Arctic Ocean needs to vent a certain amount of heat. The warmer it is, the more heat it needs to lose. So it does lose more energy, but only because that energy was already there, which is only expected to happen more and more with AGW. The end result is that it will finish losing said heat later, and winter thickening will tend to be lower. A great example is the 2016 winter, where the ice grew very slowly, and 2017 began the melting season with the lowest volume on record by far. So you are right, low ice at minimum does not mean a recovery next year, rather it means a warm year has finished.
* Sometime there will be an extraordinary event that pulls lots of stored heat from the depths, causing the ice to melt more strongly than it would have otherwise. The year after will have less stored heat, and thus could be a recovery year. It gas been claimed that the 2012 GAC was such an event, leading to the recovery years 2013-2014. I tend to share this sentiment and think it makes perfect sense, but it hasn't been proven or scientifically substantiated as far as I am aware.

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3526 on: August 22, 2020, 08:59:34 PM »
Quote
Does anybody have a list of all the remaining Ice shelves attached to Ellesmere Island or Russia with their respective sizes?
LIG, there was a great map with all the Ellesmere ice shelves and their names and their extent on given years, posted on the Ellesmere ice shelves/Ward Hunt thread and reposted in Arctic Maps recently.

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3527 on: August 22, 2020, 09:07:02 PM »
Quote
From doing a little more research, i think the ice in the first picture is probably fast ice, although now i don't understand what the difference is between fast ice and ice shelves.
I didn't check the specific case but off the top of my head, fast ice is sea ice attached to shore and/or sea bottom, normally breaking/melting every year (e.g. CAA, Kane Basin) or every few years (e.g. Jokel Bay in NE Greenland). Thickness is normally a few meters and can reach tens of meters in rare cases (grounded pressure ridges).
Ice shelf is a result of grounded glacier flow onto a floating section. Ice shelves are many tens and often several hundreds of meters thick.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3528 on: August 22, 2020, 09:13:58 PM »
<snip>
From doing a little more research, i think the ice in the first picture is probably fast ice, although now i don't understand what the difference is between fast ice and ice shelves.
<snip>
The difference is in how they are formed though that translates into differing properties.
Fast Ice is frozen sea water though it can get much thicker it is generally less than 10 meters thick. This ice has some salt content (salinity) though it decreases as it ages.
Ice Shelf is the end of a river of ice. This Ice is formed from precipitation at some elevation higher than sea level. Precipitation is freshwater not salt water. It then flows down like a river. Ice shelf's are generally much thicker being tens to hundreds of meters thick. 



p.s. too slow

Jontenoy

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3529 on: August 23, 2020, 09:50:15 AM »
Is there any publication where one can find the total nett energy balance in the Arctic at a given time . It presumably would include something like :
Energy required to melt all existing ice
Available energy in top layer of water
Incoming Insolation energy until mid Sept
Incoming energy from warm water outside the Arctic
etc etc

ajouis

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3530 on: August 23, 2020, 04:18:40 PM »
what does fractional ice mean?
After a thousand steps on the ice, it cracked.
The Man looked down at the infinite blue of the sea.
On the horizon, standing still, the polar bear had just scented his next meal.

 Less than 3000 cubic kilometers this Piomas minimum.

binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3531 on: August 23, 2020, 04:36:40 PM »
what does fractional ice mean?
At danger of being fractitious, I dare to suggest that nobody who uses this term has any clear idea what they mean by it.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3532 on: August 23, 2020, 05:10:27 PM »
I tried looking up the word and got the thirty post limit of posts.
None of them by A-team.
I give up.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3533 on: August 23, 2020, 05:26:50 PM »

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3534 on: August 23, 2020, 05:33:32 PM »
So the term is "Fractional BOE" and not "fractional ice". Fine.
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ajouis

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3535 on: August 23, 2020, 06:20:59 PM »
what does fractional ice mean?
Wrong question if this https://forum.arctic-sea-ice.net/index.php/topic,2906.msg282135.html#msg282135 contains the answer.

No such thing as a wrong question, it’s in the title of the thread, but the link you gave is mostly what I was looking for, however I am now curious on how the solid layering represented by the ice makes the fractional boe properties differ from an actual boe and whether it should, thereafter, be considered differently, probably a discussion more appropriate in another thread
After a thousand steps on the ice, it cracked.
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On the horizon, standing still, the polar bear had just scented his next meal.

 Less than 3000 cubic kilometers this Piomas minimum.

nanning

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3536 on: August 24, 2020, 11:08:26 AM »
When I read in the AbruptSLR thread about "Abrupt climate change", I do not know what that means because the meaning of the word "abrupt" is not unequivocally clear to me in this context.

In the paleoclimate/geological record, "Abrupt" probably means a period of hundreds or thousands of years. Is that correct?
If so, then anthropogenic climate change is perhaps a magnitude more 'abrupt' than what's meant by 'abrupt' in paleoclimate articles.
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kassy

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3537 on: August 24, 2020, 01:22:10 PM »
Depends on what processes you are looking at. If you look at meltwater pulse 1A the scale is a couple of centuries. If you look at the PETM you are thinking in 1000s of years and that counts as abrupt too.

So that is correct.

We beat the PETM carbon pulse so our push is more abrupt. How much quicker the SLR will be remains to be seen.
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wili

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3538 on: August 24, 2020, 02:30:28 PM »
Locally/regionally, climate change can be quite abrupt. In just a few years, rain patterns can and have changed, leaving a once well-watered area dry and a once relatively dry area drenched.

Globally, as kassy pointed out, sea level rise can be fairly quickly in the 'right' circumstance. Even though the entire 1A pulse took 4 - 5 centuries, every decade (on average) it was rising by about a half meter. That's pretty abrupt if you live anywhere near a coast.

https://en.wikipedia.org/wiki/Meltwater_pulse_1A

Since we are moving at rates faster than any previous period we can study, it is unknown exactly how fast the global system could change, especially as what had been major carbon sinks become major carbon sources, and each one of these pushes the other tipping points, etc.
« Last Edit: August 24, 2020, 02:36:54 PM by wili »
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The Walrus

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3539 on: August 24, 2020, 05:01:29 PM »
Is the ocean really physically able to lose a significant fraction of its heat content during the winter?
IIRC, one part of that equation is ice cover. Heat loss would be much higher when it's open water, and that rate drops substantially as soon as the surface freezes over.

Hopefully someone can correct me or explain it better. Because, honestly, my memory sucks!  >:(

Your memory is fine.  Heat loss does drop significantly once freeze over occurs.  The winters following the summers with the lowest sea ice minima show the largest ice growth.  Much of that has to do with the low starting point of sea ice coverage, allowing more heat to escape.  A better metric would be the ice maximum during the following winter.  Over the past 15 years, the  highest maximum occurred in 2008, following the record low of 2007 and the maximum in 2013 was not far below, following the still record low of 2012.  The sea ice maximum this year was also rather high, following last summer's low.  The only winter to not follow suit was 2017, which had the lowest sea ice maximum, following the second-lowest sea ice minimum in 2016.  The tendency is towards higher ice the following winter after a low summer minima, but the database is too small to draw any definite conclusion.

Tor Bejnar

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3540 on: August 24, 2020, 05:09:41 PM »
I understand ASLR's understanding is that mainstream science usually underestimates how fast sea level change will occur (this century, for example). The US's Climate.gov chart shows low to extreme amounts of projected sea level rise.  ASLR wants us to understand (by sharing and explaining research papers) the 'extreme' possibility is a lot more likely than the 'intermediate', and that more-than-extreme (per the chart) is in the cards.  It 'all' depends, of course, on how much CO2 (and other greenhouse-gasses) we humans cause (especially burning fossil fuels) and allow (e.g., burning ancient (and dried) peat bogs, melting permafrost), to be emitted into (and remain in) the atmosphere.  There are processes (e.g., MISI- and MICI-type mechanisms) not included in many sea level models, which cause them to underestimate what is possible.

« Last Edit: August 24, 2020, 05:23:49 PM by Tor Bejnar »
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nanning

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3541 on: August 24, 2020, 07:13:19 PM »
Thanks guys for giving your views. I understand better now.
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oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3542 on: August 24, 2020, 09:08:18 PM »
Over the past 15 years, the  highest maximum occurred in 2008, following the record low of 2007 and the maximum in 2013 was not far below, following the still record low of 2012.  The sea ice maximum this year was also rather high, following last summer's low.  The only winter to not follow suit was 2017, which had the lowest sea ice maximum, following the second-lowest sea ice minimum in 2016.  The tendency is towards higher ice the following winter after a low summer minima, but the database is too small to draw any definite conclusion.
I believe this is wrong. Normal low years achieve that status because of extra heat, which can delay freezing and result in lower ice volume the following winter. Years that achieve their low status via tapping some reservoir of energy are more prone to extra ice the following winter. In any case, looking at extent is wrong. Volume is the correct measure. IIRC max volume in 2013 was quite low, and 2017 was the lowest on record by far.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3543 on: August 24, 2020, 11:11:36 PM »
Over the past 15 years, the  highest maximum occurred in 2008, following the record low of 2007 and the maximum in 2013 was not far below, following the still record low of 2012.  The sea ice maximum this year was also rather high, following last summer's low.  The only winter to not follow suit was 2017, which had the lowest sea ice maximum, following the second-lowest sea ice minimum in 2016.  The tendency is towards higher ice the following winter after a low summer minima, but the database is too small to draw any definite conclusion.
I believe this is wrong. Normal low years achieve that status because of extra heat, which can delay freezing and result in lower ice volume the following winter. Years that achieve their low status via tapping some reservoir of energy are more prone to extra ice the following winter. In any case, looking at extent is wrong. Volume is the correct measure. IIRC max volume in 2013 was quite low, and 2017 was the lowest on record by far.
This has been discussed before, and I did some work on JAXA extent data looking at deviations from the linear trend of each years maxima and minima.

My conclusion was that there was no discernible link beyween the two.

Oren - please remind me to have a go at the PIOMAS volume data.

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Glen Koehler

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3544 on: August 25, 2020, 12:32:38 AM »
<snip> This has been discussed before, and I did some work on JAXA extent data looking at deviations from the linear trend of each years maxima and minima.

My conclusion was that there was no discernible link beyween the two.
    Walt Meier, NSIDC/NASA found the same thing.  March had no predictive power for September when you remove long-term trend.  You'd think there would some relation from an unusually high or low March starting point with subsequent September minimum, but his chart (posted months ago in the "When Will the Arctic Go Ice Free" thread) showed virtually zero correlation.  Just goes to show you how strong an influence the single-season melt weather is.  That said, this does not obviate the importance of the long term trend.  As each year carries us farther into the Alice in Wonderland rabbit hole of the new Arctic, the amount of ice will on average become less and less (as if anybody on ASIF didn't know that already, duh).

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3545 on: August 25, 2020, 03:16:14 AM »
<snip> This has been discussed before, and I did some work on JAXA extent data looking at deviations from the linear trend of each years maxima and minima.

My conclusion was that there was no discernible link beyween the two.
    Walt Meier, NSIDC/NASA found the same thing.  March had no predictive power for September when you remove long-term trend.  You'd think there would some relation from an unusually high or low March starting point with subsequent September minimum, but his chart (posted months ago in the "When Will the Arctic Go Ice Free" thread) showed virtually zero correlation.  Just goes to show you how strong an influence the single-season melt weather is.  That said, this does not obviate the importance of the long term trend.  As each year carries us farther into the Alice in Wonderland rabbit hole of the new Arctic, the amount of ice will on average become less and less (as if anybody on ASIF didn't know that already, duh).

No, there is no correlation between the March maximum and the ensuing minimum.  However, we were discussing the reverse, the relationship between the September minimum and the ensuing maximum.  As mentioned previously, there is a strong correlation between the minimum and the growth of sea ice the following winter, but much of that is a result of the lower starting point.  Still, the tendency exists for higher maxima the winter following low minima.

BornFromTheVoid

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3546 on: August 25, 2020, 09:15:07 AM »

No, there is no correlation between the March maximum and the ensuing minimum.  However, we were discussing the reverse, the relationship between the September minimum and the ensuing maximum.  As mentioned previously, there is a strong correlation between the minimum and the growth of sea ice the following winter, but much of that is a result of the lower starting point.  Still, the tendency exists for higher maxima the winter following low minima.

Scatterplot of the detrended minimum extent and following maximum extent, and line graph of the same.
There doesn't appear to be any identifiable significant relationship overall (r2 of just 0.0008).

The r2 increases if we look at just years from 2000 (0.044), and increases further for years after from 2007 (0.081), but none are close to being statistically significant.

EDIT: Looking at just the lowest 10 detrended minima gives an r2 0.26, much stronger, but still someway short of being significant.
« Last Edit: August 25, 2020, 09:22:57 AM by BornFromTheVoid »
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The Walrus

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3547 on: August 25, 2020, 03:52:45 PM »
Yes, the trend is short of scientific significance.  This is due largely to the large scatter in the data.  That does not mean that there is no correlation.  Be careful using this type of significance, as this is exactly what the deniers used to undermine global warming years ago.

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3548 on: August 25, 2020, 06:27:13 PM »
<snip> This has been discussed before, and I did some work on JAXA extent data looking at deviations from the linear trend of each years maxima and minima.

My conclusion was that there was no discernible link beyween the two.
    Walt Meier, NSIDC/NASA found the same thing.  March had no predictive power for September when you remove long-term trend.  You'd think there would some relation from an unusually high or low March starting point with subsequent September minimum, but his chart (posted months ago in the "When Will the Arctic Go Ice Free" thread) showed virtually zero correlation.  Just goes to show you how strong an influence the single-season melt weather is.  That said, this does not obviate the importance of the long term trend.  As each year carries us farther into the Alice in Wonderland rabbit hole of the new Arctic, the amount of ice will on average become less and less (as if anybody on ASIF didn't know that already, duh).

No, there is no correlation between the March maximum and the ensuing minimum.  However, we were discussing the reverse, the relationship between the September minimum and the ensuing maximum.  As mentioned previously, there is a strong correlation between the minimum and the growth of sea ice the following winter, but much of that is a result of the lower starting point.  Still, the tendency exists for higher maxima the winter following low minima.
EDIT... This exercise is giving me a headache.

I now think the Walrus is right, but also wrong.  and I was wrong - totally.
There is a correlation, but it's the opposite.

I redid the exerise using PIOMAS volume data, deviations from the linear trend, this time getting it right, i.e. comparing September minimum with the following March maximum. I also used the March & September Monthly averages, as this gets rid of any short-term spikes or dips.

I attach two graphs
- the deviations from trend by each year,
- the X-Y graph.

In most years a below trend minimum is followed by a below trend maximum.
In most years an above trend minimum  is followed by an above trend maximum.

& that's the best I can do.
« Last Edit: August 25, 2020, 06:36:20 PM by gerontocrat »
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oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3549 on: August 25, 2020, 06:31:33 PM »
Walrus claimed low Sept ice (we say volume) means high March ice (volume). You chart (and common sense) says the opposite Gero. So how is Walrus right?