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John Batteen

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3400 on: July 16, 2020, 12:18:58 AM »
Here's a stupid question.  Has anyone gone and plugged in an ice-free Arctic into an otherwise modern day starting conditions input to say, the GFS or EURO, to see how different the climate would be?  Do we have any idea how that vast swath of open water will change things?  I'm sure there's probably an entire thread on this somewhere but I'm not sure where to look.

be cause

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3401 on: July 16, 2020, 12:49:26 AM »
indeed .. as someone mentioned somewhere else .. it's not easy to find things here .. b.c.
2007 + 5 = 2012 + 4 = 2016 + 3 = 2019 + 2 = 2021 
 (phew)

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3402 on: July 16, 2020, 07:00:31 AM »
Apologies if this has been asked already and I have missed it.

What accounts for the difference in extent between NSIDC and ADS/JAXA? For example on July 12 (Before a few days of suspicious NSIDC numbers), ice extent was 7.747 million KM2, while ADS reported 7.45 million KM2, which is 300,000km2 lower, or nearly 4%?

Given this difference between the datasets is consistent, and they both use a 15% threshold for extent, can this be fully explained by using a different grid?
Different grid, JAXA is 10km, NSIDC is 25km.
But also and importantly, different satellite sensor:
Different ability to resolve coast, NSIDC has extra coastal ice that is not really there. To compensate NSIDC uses masks that change on the 1st of each month and cut off ice in regions where it surely doesn't exist. These masks were calibrated in decades past so are always late in the game.
Different susceptibility to clouds, fog, wet ice surfaces, melt ponds.

Quite consistently during the melting season JAXA extent will be lower than NSIDC, while JAXA area will be higher than NSIDC.

Phoenix

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3403 on: July 17, 2020, 06:35:41 AM »
Approximately what % of the current extraordinary decline in extent is due to ice relocation resulting from high pressure induced anticyclonic contraction?

Is it even possible to know the answer to this question? If so, how would we know?

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3404 on: July 17, 2020, 07:00:12 AM »
In principle, you should be looking at sea ice area to differentiate relocation/compaction from melt. while extent shrinks during compaction, area supposedly stays the same.
Bear in mind a lot of the damage done during the recent event is in thickness. Extreme melt does not always translate to lost area, as it requires that there was some sea ice that was on the brink of extinction. If the typical ice is still one 1 meter for example, and extreme melt strips away 50cm, very little area will be lost immediately, but that ice is doomed as bottom melt during the rest of the season will exceed remaining thickness.
Often extreme melt will hit the edges of the pack, where there is always some marginal ice ready to give up and melt out. Thus often extreme melt will correlate with area crashes, but that is not necessarily the case.

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3405 on: July 17, 2020, 07:03:10 AM »
Having stared at Worldview in awe watching the clear images of the CAB during the GAAC, I have a question of my own - is there a quantitative resource tracking cloud coverage fraction in the Arctic? Comparable with years past? Hopefully by sub-region? I am sure the information exists, but is it accessible somewhere to amateurs in easy form?

sedziobs

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3406 on: July 17, 2020, 07:09:06 AM »
Here's a stupid question.  Has anyone gone and plugged in an ice-free Arctic into an otherwise modern day starting conditions input to say, the GFS or EURO, to see how different the climate would be?  Do we have any idea how that vast swath of open water will change things?  I'm sure there's probably an entire thread on this somewhere but I'm not sure where to look.

This would be the thread to look at, though I don't know if it contains your specific request:

The Climatic Effects of a Blue Ocean Event

Phoenix

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3407 on: July 17, 2020, 07:15:52 AM »
In principle, you should be looking at sea ice area to differentiate relocation/compaction from melt. while extent shrinks during compaction, area supposedly stays the same.


This seems to assume that all of the ice on the perimeter which was recently removed from SIE as a result of compaction had previously been removed from SIA due to melt ponding or some other issue.

This seems to be a tough way to reach conclusions because of the potential noise around melt ponds draining.

Do you have an unofficial guess as to the split between the two buckets?

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3408 on: July 17, 2020, 07:29:30 AM »
This seems to assume that all of the ice on the perimeter which was recently removed from SIE as a result of compaction had previously been removed from SIA due to melt ponding or some other issue.
I am not sure why you say that. Assume that area is a noiseless measure. If compaction occurs, extent drops while area remains the same. If (final) melt occurs, extent drops while area drops. If you use AMSR2 area rather than NSIDC, especially the UH numbers provided by Wipneus on his website, the noise level will be much lower anyway.

My initial thought was that compaction was the main driver, but I've quickly come to the conclusion it was mostly melt-out of thin ice inside the pack. I can see CAB area plummeting even while compaction draws the ice from the surrounding seas into the CAB, and I can see lots of ice being lost on Worldview while racing to be compacted. However, it is best to analyze the area numbers yourself and reach data-driven conclusions, instead of relying on laypersons' gut feelings. Just remember area does not necessarily reflect on lost thickness.

Phoenix

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3409 on: July 17, 2020, 08:55:12 AM »
In principle, you should be looking at sea ice area to differentiate relocation/compaction from melt. while extent shrinks during compaction, area supposedly stays the same.


This seems to assume that all of the ice on the perimeter which was recently removed from SIE as a result of compaction had previously been removed from SIA due to melt ponding or some other issue.


So, the question is why would I conclude this.

1. I assume that any area of truly open water will register as zero ice concentration for both SIE and SIA.

2. If, as you indicate,  SIA does not shrink as a result of compaction resulting in open water while SIE does shrink....the only logical conclusion is the SIA value was already zero for the section of the map in question before the compaction event took place.

If I am missing something here, it must be very fundamental.


oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3410 on: July 17, 2020, 11:10:25 AM »
Yes, you are missing something very fundamental. The concept of grid cells and ice concentration. Remember grid cells are huge - NSIDC is 25x25 km2, and JAXA 10x10 km2. In each grid cell there can be a combination of (true) open water and (actual) ice floes. This is all represented by the sea ice concentration. Let's say of the 625 km2 of the NSIDC grid cell, 375 km2 is sea ice, and 250 km2 is open water - possibly as leads between the floes, or in some other distribution. Sea ice concentration in this grid cell will be 60% - 375/625. Sea ice extent for this grid cell will be the whole 625 km2 because concentration is above 15%.
Take an adjacent grid cell with 125 km2 of sea ice and 500 km2 of open water. Concentration is 20%, extent is 625 km2 (20%>15%).
In total we have 500 km2 of sea ice area, and 1250 km2 of extent, an average "compaction" ratio of 40%.
Now wind comes along and moves all the ice from the second grid cell to the first. Concentration rises to 80% (500/625), while in the second grid cell it drops to zero. Sea ice area remains 500 km2. However extent drops to 625 km2, a 50% reduction. This is a pure compaction event - no area was lost, but extent dropped sharply.
In another example, the weather melts 125 km2 of the 375 km2 of ice in the first grid cell. Sea ice area goes down by 25% (total of 375), extent remains the same (1250). Pure melt event.
In a third example, wind moves the ice from the second cell to the first, and weather melts 250km2 of ice. Total ice area is now 250 km2 (125+375-250) and extent is 625 km2. Average ratio is again 40%. Both have gone down by 50%. This was a melt + compaction event.

John Batteen

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3411 on: July 18, 2020, 03:11:39 PM »
Perfect sedziobs!  Just what I was looking for.  Your google-fu is stronger than mine.

Phoenix

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3412 on: July 18, 2020, 03:31:36 PM »
That makes perfect sense. Math helps.

The methodology for computing SIA is a summation of pixel concentration while SIE is binary outcome for each pixel.

I guess the difficulty in interpreting the impact of the current GAAC comes from the different sensor sensitivities. NSIDC sensors are more likely to interpret melt ponds as open water, no?

Were it not for the sensor differences, it seems that the delta between SIE loss and SIA loss points to a huge amount of compaction. But the sensor difference leaves us guessing. Is that right?



oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3413 on: July 18, 2020, 04:58:50 PM »
But was there a discrepancy between area and extent losses? Do you have the numbers, for the GAAC period, hopefully divided into 3- or 5-day slices?
Best way to verify is to check the AMSR2 extent and area (for the same periods) which suffer from different artifacts.
In order to avoid loss of information through aggregation, data should be separated to High Arctic only. Peripheral seas extent and area are irrelevant to the issue, as the compaction took place within the Arctic Basin.

Phoenix

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3414 on: July 18, 2020, 08:29:45 PM »
I appreciate the engagement Oren. I typed a long response and decided to delete it.

I think the cost / benefit of asking for your time to crawl into the weeds with so many variables to try and explain something ambiguous is not intelligent at this moment. I think its wise for me to be patient and see what evidence the rest of the season has to offer.

When the crush of the interest, opinion and curiousity regarding the melting season is past, there will be more information and more time to engage. And less stress.

Peace.

scottie

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3415 on: July 19, 2020, 12:49:49 AM »
Spotted these cloud formations on Worldview today. First between Svalbard and Franz Josef Land, second between FJL and Novaya Zemlya. I was struck by their small scale "cyclonic" appearance, don't think I've noticed anything like them before. My first thought was thuderstorm, especially the first image. The central structure in each is about 15 - 25 miles across. Just wondering if I'm correct, I'd be grateful for any insight.




Istari

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No melt on the top ?
« Reply #3416 on: July 19, 2020, 09:50:45 AM »
It looks like there are no/little melt on the top and lots on the side. Looks the same in many glaciers like these. Is there a reason for that ?
Sun melts the side? Top is higher (find this a bit un likely, since different glaciers having different height looks similar). Is this a wind thing ?

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3417 on: July 19, 2020, 10:55:42 AM »
Maybe: Top is colder thanks to higher elevation. Slopes have wind that warms as it goes down. Slope is more susceptible to low-angle sun, because it is angled itself.

blumenkraft

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3418 on: July 19, 2020, 11:14:01 AM »
For how i see it, it is melting there too. But you have a snowy surface on top and the water flows through it until it hits less porous icy layers. From there it's floating to the borders as can be seen in this Sentinel 2 picture.

Not claiming accuracy here, it's just my impression.
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JayW

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3419 on: July 19, 2020, 02:15:54 PM »
Spotted these cloud formations on Worldview today. First between Svalbard and Franz Josef Land, second between FJL and Novaya Zemlya. I was struck by their small scale "cyclonic" appearance, don't think I've noticed anything like them before. My first thought was thuderstorm, especially the first image. The central structure in each is about 15 - 25 miles across. Just wondering if I'm correct, I'd be grateful for any insight.
These mesoscale lows adre actually pretty common, especially if you look at enough RAMMB imagery. Unfortunately, I don't think they are thunderstorms (not to say nT- storms can't happen in the artic), but isee them as nteresting circulations in the mid or lower atmosphere.
This is from last year.
https://forum.arctic-sea-ice.net/index.php/topic,2649.msg205085.html#msg205085
 
Here's one today on the north coast  of Greenland.

Needs click.
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voyageur9

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Does an open CAB change everything?
« Reply #3420 on: July 19, 2020, 11:12:49 PM »
Lurker since Neven began (and I've learned a lot so much gratitude to the many who work so hard to illuminate and educate the rest of us.)

Question: When, not if, the CAB melts out does that herald an entirely new and fundamentally different freezing pattern? My understanding (albeit based on a few years doing something entirely different in the Canadian Arctic in the 70s) is that the refreeze proceeds from shore or ice-edge outwards and occurs first in calm or protected waters or leads among floes. Open ocean, open to wind reach and upwelling, unprotected by ice cover from sub-freezing atmosphere and the surface water turnover from waves is last (or never) to freeze (like the higher latitudes of the Atlantic or the circumpolar Antarctic seas. So, once there is a open CAB will the Arctic perimeter refreeze before the central ocean and could it survive a winter? Many thanks in advance.

The Walrus

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Re: Does an open CAB change everything?
« Reply #3421 on: July 19, 2020, 11:20:17 PM »
Lurker since Neven began (and I've learned a lot so much gratitude to the many who work so hard to illuminate and educate the rest of us.)

Question: When, not if, the CAB melts out does that herald an entirely new and fundamentally different freezing pattern? My understanding (albeit based on a few years doing something entirely different in the Canadian Arctic in the 70s) is that the refreeze proceeds from shore or ice-edge outwards and occurs first in calm or protected waters or leads among floes. Open ocean, open to wind reach and upwelling, unprotected by ice cover from sub-freezing atmosphere and the surface water turnover from waves is last (or never) to freeze (like the higher latitudes of the Atlantic or the circumpolar Antarctic seas. So, once there is a open CAB will the Arctic perimeter refreeze before the central ocean and could it survive a winter? Many thanks in advance.

My answer is no, it does not change the freezing pattern.  This is based on physics.  The water will still freeze starting with the calmer areas first, namely the area around the Canadian archipelago.  The sea ice will spread out from there, reaching whatever maximum that winter’s fundamentals dictate.   

oren

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3422 on: July 19, 2020, 11:44:42 PM »
Hi v9, excellent question, was much discussed in the past in various threads. This will surely affect freeze patterns, but with the long and cold Arctic winter, the ocean surface will eventually freeze, even if delayed by a few weeks. A calm and cold day will come, and the top layer will freeze and float before it has a chance to simply cool and sink. In addition, indeed seeding from the coasts of the various islands can help speed the process.

kassy

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3423 on: July 20, 2020, 12:03:57 AM »
We now have ice on top with a fresh water later below that. If you lose the ice you lose the fresh water cover and a lot of heat can come up from below and the salinity too.

It will become harder to freeze if the sun gets to shine on open water for longer because more heat accumulates.

There will be more open water so more waves.

Of course it will totally change things.

When the CAB melts out it might not be at the last date of the season and maybe most will float out instead of melt in place.
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

scottie

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3424 on: July 20, 2020, 01:41:42 AM »

These mesoscale lows adre actually pretty common, especially if you look at enough RAMMB imagery. Unfortunately, I don't think they are thunderstorms (not to say nT- storms can't happen in the artic), but isee them as nteresting circulations in the mid or lower atmosphere.

Thanks for this, I thought the first image might be a storm because there's a shadow showing the central oval being higher than surrounding cloud but it's a snapshot of a very dynamic process. I've now spotted more similar features forming in the same area. They possibly occur in clusters (?), possibly indicating unstable atmosphere close to the boundary between sea ice and open water (?) - just me thinking out loud but definitely worth looking into. Thanks again  :).

Rod

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3425 on: July 20, 2020, 01:47:56 AM »
Don’t forget the importance of latent heat of fusion. I don’t have time to type a long explanation rebutting Walrus’ theory right now. Part of what he says I agree with. But, the latent heat of fusion is something that does not get enough discussion on these forums. The ice is important in more ways than just albedo.

blumenkraft

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3426 on: July 20, 2020, 10:36:45 AM »
Scottie, check this one out. Here we have a cloud on top of it.

(found in the CAA over the Amundsen Gulf)
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johnm33

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3427 on: July 20, 2020, 11:50:08 AM »
V-9 take a look at this Atlantic penetration is for now resisted by the ice in the CAA preventing free circulation. When that ice is gone and the slush in the CAB gets flushed then the Atl. waters presently being forced to cut short their northward journey and head for Baffin/Labrador will continue into the Arctic and bathe Siberias shores with temperate waters, the cooled waters of the Arctic will push through the CAA into Baffin and Hudson, so not much chance of ice build up on the Siberian side or the CAA. If you switch to 100m depth it's clear that already saline Atl. waters are flowing through, and emerging above -1.8C we can only anticipate this continuing and reaching ever closer to being a surface current. Emerging above -1.8C is particularly significant because those channels deep cuts and smooth sides indicate that they are, in part, bounded by permafrost. We seem to be in the dubiously priviledged position of observing a great transition where the Norwegian, Greenland and all the seas through to Chukchi are to become variants of an 8C version of the Med. and warm Atlantic waters will seasonally warm Baffin from the north instead of the south.

scottie

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3428 on: July 21, 2020, 12:42:59 AM »
Scottie, check this one out. Here we have a cloud on top of it.

(found in the CAA over the Amundsen Gulf)

Thanks Blumenkraft, this mesoscale low is happening low in the atmosphere and not affecting higher layers. Again occuring close to an ice/open water boundary, I'm thinking that as air moving over sea ice crosses a boundary with open water the lowest layer experieces some warming leading to instability which cause mesolows to form which equalize the temperature differences caused by the ice/open water transition. Again just me thinking out loud following a chain of thought....don't know if it makes any sense...JayW posted this link above. It shows an area of cloud east of Svalbard moving south and passing over an ice/open water boundary, as it does so a number of mesolows form. It also looks like the whole cloud rotates clockwise....possibly conservation of angular momentum at play ????



ajouis

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3429 on: July 21, 2020, 07:53:21 PM »
What it the current thickest arctic sea ice, is it possible to still have 10 meters+ floes?
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.

Jim Hunt

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3430 on: July 21, 2020, 08:23:42 PM »
What it the current thickest arctic sea ice, is it possible to still have 10 meters+ floes?

In ridges, yes. MOSAiC found one 7 meters thick in the eastern Arctic:

Reality is merely an illusion, albeit a very persistent one - Albert Einstein

ajouis

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3431 on: July 21, 2020, 09:42:30 PM »
Thank you for the response, I am aware about the mosaic floe, but is there any evidence on the thickest floes from recent years?
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.

igs

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3432 on: July 21, 2020, 09:55:48 PM »
Thank you for the response, I am aware about the mosaic floe, but is there any evidence on the thickest floes from recent years?


The thickest is always the thickest observed while changes are huge that there will be a higher one that has not been seen yet.


What are you heading at with the questiion ?

I mean if the  thickest ice over a larger area is for example 3-4 meters what would it matter whether a 7m and a 9m etc spike would stick out of it?

Which is why i ask, perhaps you have an agenda that I've no considered or that didn't come to my mind yet.
Knowledge that does not increase every day will decrease every day !

ajouis

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3433 on: July 21, 2020, 10:31:16 PM »
Thank you for the response, I am aware about the mosaic floe, but is there any evidence on the thickest floes from recent years?


The thickest is always the thickest observed while changes are huge that there will be a higher one that has not been seen yet.


What are you heading at with the questiion ?

I mean if the  thickest ice over a larger area is for example 3-4 meters what would it matter whether a 7m and a 9m etc spike would stick out of it?

Which is why i ask, perhaps you have an agenda that I've no considered or that didn't come to my mind yet.

Yeah igs, there is indeed something behind the question, it is related to piomas thickness categories, and you can see in the hycom thread that their volume and area is not trivial even for the highest ones, which I am very skeptical about, hence the question to verify whether I was wrong about current reality or piomas was, still don’t know

Quote
As some will remember, ice in each gridcell in the PIOMAS model is specified as a discrete distribution: there exist 12 categories of ice thickness (m):
[0.00, 0.26, 0.71, 1.46, 2.61, 4.23, 6.39, 9.10, 12.39, 16.24, 20.62, 25.49]
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.

igs

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3434 on: July 22, 2020, 12:05:05 AM »

Yeah igs, there is indeed something behind the question, it is related to piomas thickness categories, and you can see in the hycom thread that their volume and area is not trivial even for the highest ones, which I am very skeptical about, hence the question to verify whether I was wrong about current reality or piomas was, still don’t know


ok, thanks for the kind elaboration  :)
Knowledge that does not increase every day will decrease every day !

Istari

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3435 on: July 23, 2020, 12:20:34 PM »
The lines marking land in worldview do anybody know the source of them ?
Reason for asking is the attach picture, could this show what’s changed since the map was made? In Most other places the fit is much better, which make me curious.

binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3436 on: July 23, 2020, 03:17:43 PM »
The lines marking land in worldview do anybody know the source of them ?
Reason for asking is the attach picture, could this show what’s changed since the map was made? In Most other places the fit is much better, which make me curious.
My guess on seeing a picture like this is that the ice has retreated from the "landline" - I forgot to check the scale, and the picture took ages to download so I'll leave that to someone with a faster connection, but a retreat of some hundreds of meters would not be that unusual.
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igs

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3437 on: July 23, 2020, 03:39:10 PM »
The lines marking land in worldview do anybody know the source of them ?
Reason for asking is the attach picture, could this show what’s changed since the map was made? In Most other places the fit is much better, which make me curious.


To be honest, I don't think that this is the reason why they're off.

It's quite normal in many maps that try to draw lines along coasts that they are approximate and by no means accurate.

It could be that they're there to mask land once clouds block satellite views or there might be different motives depending on the map provider, not sure either.
« Last Edit: July 23, 2020, 04:21:32 PM by igs »
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blumenkraft

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3438 on: July 23, 2020, 03:45:11 PM »
I think this illustrates the problem. The more edges, the more accurate is the map. If you reduce edges, you reduce complexity, which is wanted in some cases.

A Map of Germany made from 4 to 700 edges

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binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3439 on: July 23, 2020, 05:46:03 PM »
And yet the "land line" follows the coast very closely into every inlet and fjord, except where there is a glacier extending into water where the landline could well have marked the maximum extent of that glacier when the map making was done (which could well have been very early last century).

Reminds me of one summer in 2005 when I drove to a spot where I used to go with my kids some 10 years earlier because the glacier tongue nearby was very flat and easy to walk up on. But in 2005 the glacier had retreated several hundred meters from where we used to walk onto it, and a large lake had formed inbetween.

But the strangest thing was when I looked at my GPS and it showed me more then 100 meters up on a glacier tongue that obviously was not there anymore. So between the GPS map and 2005 the tongue had retreated by at least 300 meters, probably more.

Having checked the scale of the posted image above, I would say that the most likely explanation is the obvious one: The glacier tongues have retreated since the maps were made, and the "landline" shows the extent then, while the image shows the extent now.
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 #3440 on: July 23, 2020, 05:52:14 PM »
binntho:
I'm surprised it's that little. 300 m/decade is 30 km/millennium and I would have thought they were shrinking faster than that.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3441 on: July 23, 2020, 09:24:10 PM »
The lines marking land in worldview do anybody know the source of them ?
Reason for asking is the attach picture, could this show what’s changed since the map was made? In Most other places the fit is much better, which make me curious.
Maybe the now open bays were covered with permanent ice shelves at the time when the "land boundary" was defined. Since then some of the small shelves have melted completely.
In the Amundsen bay region in the Antarctic you can also see the position of the shelves when the "boundaries" were defined. In addition the maps also show an additional "boundary" that separates the shelf from the land, which is not always in congruence with the actual shore line respectively the calving front.

I have no idea whether an update is planned from time to time to adjust the coast and shelf positions.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3442 on: July 23, 2020, 09:52:29 PM »
Today I was looking at some areas where floes are moving pretty rapidly, e.g., the Nares Strait.  Here, rapidly means maybe a slow walk, say 0.5 - 1.0 km/hr.  But it got me wondering, with chunks of ice floating around, running into each other and scraping past, and so on...is it noisy?  Seems like it could be quite loud.  Maybe someone who's actually been around this kind of activity can fill me in on what it sounds like?  Thanks!
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3443 on: July 23, 2020, 09:59:22 PM »
Hopen Times would be the person you are looking for to answer this question. Hope they see it.
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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3444 on: July 23, 2020, 10:17:28 PM »
Today I was looking at some areas where floes are moving pretty rapidly, e.g., the Nares Strait.  Here, rapidly means maybe a slow walk, say 0.5 - 1.0 km/hr.  But it got me wondering, with chunks of ice floating around, running into each other and scraping past, and so on...is it noisy?  Seems like it could be quite loud.  Maybe someone who's actually been around this kind of activity can fill me in on what it sounds like?  Thanks!
     Different setting but same idea.... I once happened to be next to local river when the winter ice jam broke on warm April afternoon and the sound was impressive.  Grind... crash...thud...groan... crack!

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3445 on: July 23, 2020, 11:05:41 PM »
From a novel written by a author who knew the Far North (no, not Jack London).

Quote
His lungs drank in the ice-tanged air. But it was not cold. Kwaske-hoo—the change—had come. The air was filled with the tumult of the last fight of winter against the invasion of spring, and the forces of winter were crumbling. The earth under Keith's feet trembled in the mighty throes of their dissolution. He could hear more clearly the roar and snarl and rending thunder of the great fields of ice as they swept down with the arctic current into Hudson's Bay.
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binntho

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3446 on: July 24, 2020, 06:30:46 AM »
binntho:
I'm surprised it's that little. 300 m/decade is 30 km/millennium and I would have thought they were shrinking faster than that.
Well I'm not sure what you expect. The glaciers in Iceland have been melting very fast, and the glacier tongues retreating. Some of the biggest retreat is in the area shown in this image, the longer red line is by far the furthest retreat of any land-grounded glacier tongue that I know of.

The shorter line shows the retreat of the glacier I was talking about. The red cross shows where I used to park my car, the two blue lines show the maximum extent and the extent during the late nineties.

The maximum extent was reached some 100 years ago.

The glacier tongues are outlets, of the mother glacier, so a shortening of the tongue is can be thought of as a response to a decrease in the mass of the supplying glacier behind it. And this can be very readily seen when you visit the area and know it from before, the ice has thinned noticeably and I believe that the Vatnajokull glacier (which is the biggest) is losing som 10% of mass per decade.

At some point the mother glacier will not have enough mass to supply the glacier tongue. At that point it will stop moving and melt down in situ. I've seen this happening to shorter stretches of tongue, a large section can disappear very quickly. When that point is reached, I'd think you would see retreat in the range of several kilometers every year.

Edit: Sorry about the large image, a click will open it in larger scale.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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dnem

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3447 on: July 26, 2020, 12:00:22 AM »
Right now Hurricane Hanna is at around 973 mb and 80 kts. The Beaufort low is predicted to bottom out around the same central pressure but the predictions I see are for perhaps 40 or 45 kts.

Why the difference?

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3448 on: July 26, 2020, 06:50:24 AM »
Right now Hurricane Hanna is at around 973 mb and 80 kts. The Beaufort low is predicted to bottom out around the same central pressure but the predictions I see are for perhaps 40 or 45 kts.

Why the difference?
Wind velocity is a factor of the pressure gradient rather than the absolute pressure. Crudely, the closer the isobars, the faster the potential wind. Meteorologists will likely jump all over me....

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Re: "Smart" and "Stupid" Questions - Feel Free To Ask
« Reply #3449 on: July 26, 2020, 01:29:25 PM »
Thanks Sebastian. I am aware of that, but it seems that the lows in the arctic have consistently lower wind speeds for a given central pressure.