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Author Topic: Peripheral Seas of the Arctic Basin Seasonally ice free state  (Read 29988 times)

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #50 on: May 27, 2015, 10:05:15 PM »
The primary problem I have with the fast collapse idea is merely winter thickness. Unless that collapses it poses a major obstacle to a fast collapse - the sheer volume of ice in the Arctic Ocean. The PIOMAS -1m experiment is the sort of exploration of principle seen in Tietsche et al - a 'what if' experiment. And even with that drop of 1m winter thickness, the Arctic ocean retains a central core of ice that survives the summer.

When I say 'how fast' I'm thinking whether the IPCC will be right (after 2040s), which I doubt. Or whether we're looking at 2030 (-5, +10 years).

I can't find the quote, but Dr Zhang (of PIOMAS) has said that with winter warming he thinks the 2020s could see [really low extents] - I have to vague here because I can't find the quote.

Rick Aster

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #51 on: May 29, 2015, 12:05:30 PM »
Quote
The primary problem I have with the fast collapse idea is merely winter thickness. Unless that collapses it poses a major obstacle to a fast collapse - the sheer volume of ice in the Arctic Ocean. ... And even with that drop of 1m winter thickness, the Arctic ocean retains a central core of ice that survives the summer.

Ice thickness is an obstacle to melting only as long as the ice stays in place. That is a given if the central pack is large and penned in on all sides, but less so as the surrounding seas open up. Ice drift speeds would not have to exceed 2 km per hour to export the entire central pack in one season.

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #52 on: May 29, 2015, 01:29:32 PM »
Yet future modelling studies with low extent show thickest ice where it is thickest in recent decades.

crandles

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #53 on: May 29, 2015, 04:33:49 PM »
And even with that drop of 1m winter thickness, the Arctic ocean retains a central core of ice that survives the summer.

If you modelled this over more than one season (possibly several needed to transport thick ice out to where it would melt) with winter thermo thickening (somehow? warmer winter temps?) only getting up to max thickness of about 1.3m (only a fall of about 0.5- 0.7m rather than a full 1m thinning), there would be significantly less mass of ice in winter which would cause less ridging / slabbing etc so over several years of transport replacing the thick ice, it seems to me the thick ice could well drop in average thickness by much more than 1m.

Do you believe that these sort of effects would not occur? or
They might occur, but even if they did the Arctic ocean near CAA/Greenland would still retain a central core of ice?
Or might the Arctic ocean actually get pretty close to melting out?

Rather than remove 1m everywhere, would a few experiments one removing 15% of thickness everywhere, one removing 20% of thickness everywhere, ... be better?

Or might Tiesche et al like future projection data be queried to provide a better indication of how to distribute some thinning?

jdallen

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #54 on: May 29, 2015, 05:22:31 PM »
Quote
The primary problem I have with the fast collapse idea is merely winter thickness. Unless that collapses it poses a major obstacle to a fast collapse - the sheer volume of ice in the Arctic Ocean. ... And even with that drop of 1m winter thickness, the Arctic ocean retains a central core of ice that survives the summer.

Ice thickness is an obstacle to melting only as long as the ice stays in place. That is a given if the central pack is large and penned in on all sides, but less so as the surrounding seas open up. Ice drift speeds would not have to exceed 2 km per hour to export the entire central pack in one season.

Import of warmer surface water will start coming into play as more sea surface captures insolation, longer.  That mechanism had a big part to play last year with the "Laptev Bite".

Import of warmer water from the Barents and Bering will be a factor, though the Bering may have the more immediate effect on MYI in the Chukchi and Beaufort.

Eventually the core pack loses, either to getting moved to warmer water, or being exposed to influxes of warmer water from peripheral seas.
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ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #55 on: May 29, 2015, 07:32:33 PM »
Crandles,

Thinner ice means more ridging as the compressive strength declines substantially. e.g. Zhang et al 2012 "Recent changes in the dynamic properties of declining Arctic sea ice: A model study"

I can only repeat that the modelling studies show the survival of ice off the CAA. For example here is PIOMAS.
http://psc.apl.washington.edu/zhang/IDAO/predict.html
Click on the years to get the projection. What is the common factor? It's that there is a survival of late summer ice off the CAA, even in the latest projection (end of this century). For such a feature to be so universal has the same implication of the universal loss of modelled sea ice with enthropogenic forcing, and no loss without anthropogenic forcings. That the models as a group are picking up some universal physical reason for the behaviour.

One issue that occurs to me: The deeps of the Arctic Ocean are under the Central Arctic. Nghiem notes the 'concidence of MYI and the edge of the Canada Basin
Nghiem 2006
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120003985.pdf
Canada Basin
http://geology.com/articles/arctic-ocean-features/arctic-ocean-seafloor-map.jpg

But Nghiem does not explain that 'coincidence' (unless I missed it), and we see it again this year:
http://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticictnnowcast.gif

Is there something about the deeps that makes melting ice harder? Melt makes a fresh warm cap of water (less dense), so why would depth matter?

Now that I've finished with my 'slow transition' argument, this might make an interesting diversion. I'll have a dig around and might email someone.

johnm33

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #56 on: May 29, 2015, 11:45:25 PM »
ChrisReynolds
"Is there something about the deeps that makes melting ice harder? Melt makes a fresh warm cap of water (less dense), so why would depth matter"
My 2c any swell passing through the deep will generate waves as it meets any shallower water, any waves/swells passing across the shallows will disappate as it meets deep water. More waves more broken ice more surface area.

Bruce Steele

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #57 on: May 30, 2015, 12:44:13 AM »
I have been wondering about the transfer of warm water from the Pacific through the Aleutians  and via the Alaskan Coastal current into the Beaufort and Chukchi Seas. Wood et 2015

http://www.sciencedirect.com/science/article/pii/S0079661115001020

From the article



"Steele et al 2010 showed that 80% of the ocean heating in the Pacific Arctic north of Alaska is from ocean heat flux, and only 20% due to ocean lateral heat flux( e.g. Bering Sea inflow), which mostly occurs within a few hundred kilometers from the coast. Moreover, the movement of Pacific Water from the Aleutian Passes to BeringStrait takes more than one year, with the exception of the small
portion that enters the shelf through the Zemchug Canyon, which takes 8 months.
Hence , most of the water of Pacific origin entering the Bering Strait has gone through a seasonal cycle on the journey and thus cooled to near freezing ( -1.8 *C )
( Stabeno et al, in press ) as reflected in the low temperatures recorded at the mooring array in the Strait."
" This would imply that most of the warm water advected into into the Bering Strait ( and available to melt sea ice ) must be heated in transit from the atmosphere ( insolation and downward long wave radiation ) in the Northern Bering  Sea ( Woodward et al 2010 ) "

   It seems to me there will be much more advection of Pacific heat via the Alaskan Coastal Current when the Bering Sea warms to the point that Bristol Bay and Norton Sound stay mostly ice free year round. Then summer insolation and long wave radiation will work on coastal waters for longer periods and that heat can then move into the Beaufort and Chukchi earlier.  I am not going to speculate on when this may happen but when the ACC starts with water above -1.8 C  each spring the extra heat moved North will add substantially to current heat transfer from the Pacific.
 Neven speculated on the effects of the Pacific warm water "blob" over on the Sea Ice Blog last post before vacation .   


crandles

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #58 on: May 30, 2015, 03:32:54 AM »
Crandles,

Thinner ice means more ridging as the compressive strength declines substantially. e.g. Zhang et al 2012 "Recent changes in the dynamic properties of declining Arctic sea ice: A model study"

I can only repeat that the modelling studies show the survival of ice off the CAA. For example here is PIOMAS.
http://psc.apl.washington.edu/zhang/IDAO/predict.html
Click on the years to get the projection. What is the common factor? It's that there is a survival of late summer ice off the CAA, even in the latest projection (end of this century). For such a feature to be so universal has the same implication of the universal loss of modelled sea ice with enthropogenic forcing, and no loss without anthropogenic forcings. That the models as a group are picking up some universal physical reason for the behaviour.

Thanks for the link.

The February images are interesting. For 2005, 2015, and 2025 there is some thinning at the fringes but basically the ice that is 2-2.5m thick in 2005 and 2015 remains 2-2.5m thick even to 2045 (and strangely seems thicker in 2025). The thinning is all at the fringes and from the thickest ice.

Therefore removing 1m from everywhere does not seem a realistic distribution for a significant thinning.

This would seem to be evidence pointing towards less thick ice despite the thinner ice having less compressive strength.

I would accept 'more' ridging in thinner ice - just that it doesn't ridge as high because of less mass and possibly also less time to thicken through dynamic processes if the ice gets transported out of smaller thick ice areas in less time.

.

2.8C warmer temperatures (2045 projection) and ice in Laptev and ESS remains in the 2-2.5m thick band seems optimistic as well as the thicker Central Arctic ice on Russian side in 2025 compared to 2015 noted above. PIOMAS already has it less than 2m for April 2015.

Therefore those PIOMAS projections look very optimistic to me and maybe not very reliable.

Yes there is a common feature of ice near Greenland/CAA surviving. I would suggest there is a major difference between Laptev/ESS where ice moves away from these regions leaving open ocean to absorb more energy and near GL/CAA where any gaps through leads and melting tend to get filled by ice moving into the area. There could well be a lot of more complicated reasons as well or instead.

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #59 on: May 30, 2015, 09:06:54 AM »
John,

There is a line in a paper that says roughly that the shallower seas warm faster than the deeper once ice free in the summer. But I can't remember what paper! It might be that there is some diffusion of heat downwards that is significant.

Bruce,

Thanks, I have that paper, but had forgotten that conclusion. Warmer Pacific inflow earlier in the season should help get things started off Siberia.

Crandles,

As with GCMs I find the long term projection of ice cover unlikely, and I doubt the winter thickness will hold up so long (winter doesn't thin as I would expect). My point in presenting those is merely to show that throughout the recession of ice the summer shows surviving ice along the Canadian Arctic Archipelago.

There might be a rare summer driven by rare weather that causes a blob of ice in the middle of the Arctic Ocean, but the overall behaviour is not like that. I am not persauded by arguments relying on extremely unusual events, especially given the findngs of Tietsche et al - after a very unusual summer ice will recover.

I have been looking at Gice trying to figure out if a subset of the thickness distribution levels might allow me to work out thermodynamic thickening.

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #60 on: October 04, 2015, 12:46:52 PM »
This follows on from a throw-away justification of a statement in my most recent blog post....

How do we define seasonally ice free? The ultimate definition is no ice at all, but that is too long a prospect for me. So I turn to virtually sea ice free...

The common definition seems to be total NH sea ice area extent of less than 1M km^2. But how might we apply this to the regional seas of the Arctic?

Average September extent for the 1980s in Wipneus's data set (near as damn it NSIDC Extent), was 7.219M km^2. 15% seems to be a good demarcation for working out extent, so let's try applying that to overall Arctic extent. 7.219M X 0.15 = 1.083M km^2. That's only a bit above the 1M km^2 level below which the Arctic Ocean can be considered virtually sea ice free.

So I propose that September extent of below 15% of 1980s September extent means that sea/region is virtually sea ice free.

Looking at the regions available:

Okhostk - ice free in summer most of the record - discounted.
Bering - ice free in summer most of the record - discounted.

Beaufort 1980s average is 0.34M km^2 - OK
Chukchi 1980s average is 0.25M km^2 - OK
ESS 1980s average is 0.67M km^2 - OK
Laptev 1980s average is 0.34M km^2 - OK
Kara 1980s average is 0.30M km^2 - OK

Barents - 1980s average only 0.07M km^2 - discounted.

Greenland Sea 1980s average is 0.30M km^2 - OK
Central Arctic 1980s average is 4.40M km^2 - OK
CAA 1980s average is 0.44M km^2 - OK

Baffin - ice free in summer most of the record - discounted.
Hudson - ice free in summer most of the record - discounted.
St Lawrence - ice free in summer most of the record - discounted.

Of the regions accepted as having a reasonable amount of ice in the 1980s during September, Central, Greenland and the CAA have no years with less than 15% of the September average. That leaves us with Beaufort round to Laptev, the peripheral seas of the Arctic Basin, and the Kara Sea.

The list below shows the regions concerned that do show a (virtually) ice free state in September.
1 means ice all year (>15% of 1980s September extent). 0 means ice free (<15% of 1980s September extent)


   Beaufort   Chukchi   ESS   Laptev   Kara
1979   1   1   1   1   1
1980   1   1   1   1   1
1981   1   1   1   1   1
1982   1   1   1   1   1
1983   1   1   1   1   1
1984   1   1   1   1   1
1985   1   1   1   1   1
1986   1   1   1   1   1
1987   1   1   1   1   1
1988   1   1   1   1   1
1989   1   1   1   1   1
1990   1   1   1   1   1
1991   1   1   1   1   1
1992   1   1   1   1   1
1993   1   0   1   1   1
1994   1   1   1   1   1
1995   1   1   1   0   0
1996   1   1   1   1   1
1997   1   1   1   1   1
1998   0   1   1   1   1
1999   1   0   1   1   1
2000   1   1   1   1   1
2001   1   1   1   1   1
2002   1   0   1   1   1
2003   1   0   1   1   1
2004   1   0   1   1   1
2005   1   0   1   1   1
2006   1   1   1   1   1
2007   1   0   0   1   1
2008   0   0   0   1   1
2009   1   0   1   1   1
2010   1   0   1   1   1
2011   1   0   1   0   1
2012   0   0   0   0   1
2013   1   0   1   0   1
2014   1   0   1   0   1

Update for 2015's melt season, using all the same assumptions and conditions for the above original post on this thread. This time I have added a column for Peripheral Seas (Beafort, Chukchi, ESS, Laptev).

1 means more than 15% of the 1980s September extent.

0 means less than 15% of the 1980s September extent.

0 is taken to be a year which meets the regional condition of 'virtually ice free'.

Year   Beaufort    Chukchi   ESS   Laptev   Kara   Peripheral
1979   1   1   1   1   1   1
1980   1   1   1   1   1   1
1981   1   1   1   1   1   1
1982   1   1   1   1   1   1
1983   1   1   1   1   1   1
1984   1   1   1   1   1   1
1985   1   1   1   1   1   1
1986   1   1   1   1   1   1
1987   1   1   1   1   1   1
1988   1   1   1   1   1   1
1989   1   1   1   1   1   1
1990   1   1   1   1   1   1
1991   1   1   1   1   1   1
1992   1   1   1   1   1   1
1993   1   0   1   1   1   1
1994   1   1   1   1   1   1
1995   1   1   1   0   0   1
1996   1   1   1   1   1   1
1997   1   1   1   1   1   1
1998   0   1   1   1   1   1
1999   1   0   1   1   1   1
2000   1   1   1   1   1   1
2001   1   1   1   1   1   1
2002   1   0   1   1   1   1
2003   1   0   1   1   1   1
2004   1   0   1   1   1   1
2005   1   0   1   1   1   1
2006   1   1   1   1   1   1
2007   1   0   0   1   1   1
2008   0   0   0   1   1   1
2009   1   0   1   1   1   1
2010   1   0   1   1   1   1
2011   1   0   1   0   1   1
2012   0   0   0   0   1   0
2013   1   0   1   0   1   1
2014   1   0   1   0   1   1
2015   0   0   0   0   1   0

In 2015 most of the regions here were seasonally ice free, the last time 4/5 met this condition  was in 2012. Only in 2012 was the composite region Peripheral Seas also virtually ice free.

Bruce Steele

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #61 on: October 04, 2015, 02:30:45 PM »
Chris, Would any of the discounted seas have been counted if you were to choose the 70s or the 60s as your baseline? I suppose I am being lazy but I figure you could answer this fairly easily. Anyway it's great to see you back and I have checked dosbat a couple times over the last month. Hope you got in some vacation. You said there you weren't feeling to driven to post so often of late and I figure that's probably healthy. I am here every day....maybe a borderline addiction . 

jdallen

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #62 on: October 04, 2015, 08:47:19 PM »

<snippage>
Update for 2015's melt season, using all the same assumptions and conditions for the above original post on this thread. This time I have added a column for Peripheral Seas (Beafort, Chukchi, ESS, Laptev).

1 means more than 15% of the 1980s September extent.

0 means less than 15% of the 1980s September extent.

0 is taken to be a year which meets the regional condition of 'virtually ice free'.

Year      Beaufort    Chukchi   ESS         Laptev   Kara          Peripheral
<snippage>
2015       0          0         0           0         1            0

In 2015 most of the regions here were seasonally ice free, the last time 4/5 met this condition  was in 2012. Only in 2012 was the composite region Peripheral Seas also virtually ice free.
I thought the Kara melted out?  It certainly looks like it based on my understanding of what area the name encompasses.  See attached a 5KM grid image from EOSDIS Worldview from September 14th.

It seemed to me this year, they *all* melted out...
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crandles

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #63 on: October 04, 2015, 10:18:54 PM »

I thought the Kara melted out?  It certainly looks like it based on my understanding of what area the name encompasses.  See attached a 5KM grid image from EOSDIS Worldview from September 14th.

It seemed to me this year, they *all* melted out...

Seems Kara often leaves a little bit unmelted:


Not sure if that is due to transport from CAB to Kara or some sea ice hanging on by Severnaya Zemlya.

Last 11 years, it seems area got down to around 5% of the April area. In the 80s' it was much more variable. That sort of seems like a new state - an 'almost always seasonally virtually ice free' state rather than sometimes virtually ice free. Not sure that that would justify changing a 15% of 80s' September Extent definition though. There might need to be different styles of definitions for different purposes.

Possibly it suggests that always using the 80s' as a reference period might not be sensible - If some regions become seasonally virtually ice free earlier than other areas should the reference period also vary with how soon it starts to be almost always seasonally virtually ice free? If you specify a fixed reference period like the 80s' don't you start comparing some regions to 15% of a low extent level, while other regions are compared to 15% of a fairly high extent?

I am not really sure if something like 5% of current typical April area (or extent possibly with a different percentage than 5%) might be better than 15% of September extent from the 80s'.

The 15% being a similar cut off to that used elsewhere seems nice but when one is 15% of the total area in the cell and the other is 15% of September extent levels of the 80s' they are rather different beasts and the cut off similarity should perhaps be considered spurious rather than a nice consistency?

There may be good reason for not using 5% of typical April level. Just thought I would mention the possibility and what might be seen as a potential problem with the 15% of 80s' extent.

jdallen

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #64 on: October 05, 2015, 07:28:01 AM »
I think we can agree that the ice cover is anomalously *low*, whether we use the baseline you chose, or that which was suggested by others.

The random 100K km2 the Kara seems to have strikes me as the last residual effort by a desperate individual hanging from a window ledge before succumbing to gravity.

To your point, it is very clear, the ice is no better off than it was at the end of 2012, which bodes very unfavorably for our future.  I think your metric is fine, and in fact fairly conservative in describing just how bad things are.  That last would be my only criticism of it, but in that, might still make it more palatable to someone wavering on the edge of being convinced we need to do something, as compared to my strident screams of alarm  ;D

How 2016 goes now depends greatly on the refreeze; more than previously.  We've established I think that the "symmetry point" in the system has changed.  So much so, that an average melt year could put us into a virtual tie with the third worst ice melt back in modern record.  If we see imports of heat into the winter Arctic, and significant snowfall over the pack (which I think is probable), an average melt year next year will likely take us past 2015 into 2012 territory, as it took us that past 2014 this year into 2011/2007 territory.

Of course, all bets are off if we get melt conditions like 2012.  In such an event, we may find ourselves apologizing to Wadhams for not taking him more seriously.
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ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #65 on: October 05, 2015, 08:22:49 AM »
Chris, Would any of the discounted seas have been counted if you were to choose the 70s or the 60s as your baseline? I suppose I am being lazy but I figure you could answer this fairly easily. Anyway it's great to see you back and I have checked dosbat a couple times over the last month. Hope you got in some vacation. You said there you weren't feeling to driven to post so often of late and I figure that's probably healthy. I am here every day....maybe a borderline addiction .

Borderline addiction - yes I have reflected on that. I'm still on a sort of break but have had a really bad cold that in retrospect has been the flu, all my joints and various old injuries are killing me right now! I'm currently working through the spectrum of energy received by a loop antenna from a few Hz to 50MHz - the game is - can I identify all of the peaks and spikes? But I am too wiped out to carry on with that right now.

Sorry I don't have data from the 60s or 70s. If Chapman/Walsh isn't too flat (and it may be) one could extend the 1980s data back, so it wouldn't change much.
« Last Edit: October 05, 2015, 08:35:10 AM by ChrisReynolds »

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #66 on: October 05, 2015, 08:38:30 AM »
JD Allen,

In Wipneus's data the 1980s September average extent was 0.299, this September was 0.064, that's 22%. There may be some phantom ice involved here that will disappear when the data is reviewed by NSIDC and transferred from 'nrt' files to 'final'. But at present I have to report the data as it stands, sorry.

Crandles,

As stated in the original post, a common definition for virtually ice free in the NH is 1 million kmsq. This is roughly 15% of the 1980s September extent, I cannot help but wonder if this is by accident or design as 15% is conveniently the level used to determine extent itself. Applying the same criterion to regions as one would use for NH ice seems to be a neater approach to me than trying to establish a different criterion.

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #67 on: October 05, 2015, 06:07:16 PM »
JD Allen,

In Wipneus's data the 1980s September average extent was 0.299, this September was 0.064, that's 22%. There may be some phantom ice involved here that will disappear when the data is reviewed by NSIDC and transferred from 'nrt' files to 'final'. But at present I have to report the data as it stands, sorry.

No need to be sorry; your thinking (and Wipneus's) is consistent, rigorous and sound.  You shape your conclusions to the data rather than the reverse; I'd be disappointed if you did anything less.

Crandles,

As stated in the original post, a common definition for virtually ice free in the NH is 1 million kmsq. This is roughly 15% of the 1980s September extent, I cannot help but wonder if this is by accident or design as 15% is conveniently the level used to determine extent itself. Applying the same criterion to regions as one would use for NH ice seems to be a neater approach to me than trying to establish a different criterion.

Sounds completely consistent with conventional practice.  I agree, there would need to be some obvious pressing reason to establish a different criterion, and we'd want to see the justification for it laid out.  I say also, using the current criterion does not detract one jot from the conclusions we can draw from your analysis.  They are obvious and disturbing.
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Steven

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #68 on: October 05, 2015, 08:23:14 PM »
There may be some phantom ice involved here

The NSIDC maps have some "phantom ice" in the estuaries of the Ob and Yenisei rivers:



which is probably the reason why Kara Sea isn't  "virtually ice free" according to your definition. Perhaps you could modify the definition a bit, to get rid of this phantom ice in the Yenisei Gulf and in the Gulf of Ob?

sedziobs

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #69 on: October 05, 2015, 08:30:39 PM »
Wipneus did a nice comparison showing the false ice a few years ago:
http://forum.arctic-sea-ice.net/index.php/topic,563.msg14447.html#msg14447

If that's included in the Kara data, then it seems the Kara Sea will never be ice free as defined in this thread.


ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #70 on: October 05, 2015, 08:46:18 PM »
JD Allen,

Yes, it does seem to support what we already know - the peripheral seas are acting as leaders for the entire Arctic. At some point it might be worth defining two (or more?) regions within the CAB, one that will hold the remnant ice off the CAA in the latter stages of the transition and one that will be next in line to fall once the peripheral seas have transitioned.

Steven,

I've just taken the numbers based on the preliminary 'nrt' data, and am loathed to start messing around with them. At present Wipneus's calculations are to within a fraction of a % for the official NSIDC Sea ice index NH extent if we* start applying our own masks then we'll have a different product which still might change when the data goes from prelinary to final at the start of the following year.

* I say 'we' because Wipneus is producing the data, but I have my own code ready to go and have kept notes of discussions Wipneus has had with someone else about the correct application of masks. So in theory I could make the same numbers, but Wip's coding is far more automated than my approach (using Visual Basic) and it's easier for me to just use his numbers.

oren

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #71 on: October 06, 2015, 01:12:24 AM »
I think the problem with Kara is that it's been seasonally ice-free for most of the record based on eyeballing the chart, and should have been discounted the way that Barents for example was discounted.
The problem is that "seasonally ice-free" is defined here compared to 80s baseline, but if the 80s baseline was already on its way to seasonally ice-free then we get a flawed baseline, IMHO.

More importantly, I find it very interesting that Chukchi and more recently Laptev seem to have become seasonally ice-free where once they were not. Despite strong winter freezing they manage to melt during the summer. It seems the Beaufort and the ESS are partly on their way to become so as well. Once this transition is completed, the CAB should have a harder time resisting a strong seasonality.

ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #72 on: October 07, 2015, 07:36:11 PM »
Oren,

Quote
Barents - 1980s average only 0.07M km^2 - discounted.
Kara 1980s average is 0.30M km^2 - OK
Laptev 1980s average is 0.34M km^2 - OK

Barents 1980s extent for September was 0.07, less than 1/3 of Kara, Kara 1980s extent was similar to that of Laptev, which is transitioning.

Once the peripheral seas become regularly seasonal the interesting action in those seas should be the ice edge receding earlier. It is this which should really allow the ice edge to penetrate the Central Arctic. That will be interesting, but at the moment penetration in the Central region seems to be relatively late.

jdallen

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #73 on: October 08, 2015, 07:00:36 AM »
Oren,

Quote
Barents - 1980s average only 0.07M km^2 - discounted.
Kara 1980s average is 0.30M km^2 - OK
Laptev 1980s average is 0.34M km^2 - OK

Barents 1980s extent for September was 0.07, less than 1/3 of Kara, Kara 1980s extent was similar to that of Laptev, which is transitioning.

Once the peripheral seas become regularly seasonal the interesting action in those seas should be the ice edge receding earlier. It is this which should really allow the ice edge to penetrate the Central Arctic. That will be interesting, but at the moment penetration in the Central region seems to be relatively late.

Yes, and indeed it is relatively late - not until mid August this year in fact.

One think I will be watching with a view in mind of end-of-refreeze thickness is snowfall.  It strikes me that we now have ready sources of moisture with moderately high temperatures directly adjacent to the central pack, in addition to what now appears to be steady inflows of heat and moisture from lower latitudes.  That moisture is readily available to start dumping precipitation on newly formed ice.  I doubt this is optimal for recovery.
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ChrisReynolds

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #74 on: October 09, 2015, 08:35:47 PM »
Cohen has done work on the link between sea ice loss and cold NH winters, this is mediated by increased early winter precipitation of snow due to late season open water in the Arctic Ocean. That link being shown by the unique isotopic composition of Arctic Ocean water being detected in snow fall over Eurasia.

Assuming cold enough conditions for the newly formed pack ice to have a dry surface, surely it is not beyond reason to suspect that early winter precipitation of snow over the Arctic Ocean ice pack itself may be increasing. And an insulating blanket of snow over thinning ice early in the winter (Oct - March) season would reasonably be expected to reduce winter thickening significantly.

The PIOMAS -1m experiment implies that to get massive inroads into the Central Arctic we need to see substantially thinner winter ice. Increased early winter snowfall might play a role in this.

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Re: Peripheral Seas of the Arctic Basin Seasonally ice free state
« Reply #75 on: October 10, 2015, 11:54:40 AM »
isn't there is a negative feedback that as end of summer extent gets lower, a lot of the autumn snow falls on open water, leading to a thinner insulating layer(?) crandles has posted sth on this in the refreeze thread
« Last Edit: October 10, 2015, 12:07:29 PM by sofouuk »