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Author Topic: Latest PIOMAS update (May 2019)  (Read 937149 times)

seaicesailor

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Re: Latest PIOMAS update (June)
« Reply #600 on: June 09, 2015, 12:52:29 AM »
Quote
PS Beaufort is the thinnest and lowest volume on record!

But that's where a lot of the MYI is...  ??? :-\

Well, in absolute terms, thickness is large in Beaufort this year, only that in earlier years it was probably more multi and more thick (pardon my english)

jdallen

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Re: Latest PIOMAS update (June)
« Reply #601 on: June 09, 2015, 03:37:53 AM »
Quote
PS Beaufort is the thinnest and lowest volume on record!

But that's where a lot of the MYI is...  ??? :-\
As I said elsewhere, we are in entirely unknown territory.

What is necessary now to save us from a new record minimum, is the best of possible weather to preserve the ice.

Poor melt conditions (e.g. 2013) might keep us in the bottom 5.

Even average melt conditions will put us into the bottom three, if not the bottom two or even lower than 2012.

Conditions optimal for melt will be catastrophic.
This space for Rent.

jdallen

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Re: Latest PIOMAS update (June)
« Reply #602 on: June 09, 2015, 03:42:35 AM »
P.S. - bets on whether or not Peter Wadhams will be saying "I told you so!" at the end of the season?

Cold comfort....
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Vergent

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Re: Latest PIOMAS update (June)
« Reply #603 on: June 09, 2015, 03:51:30 AM »
Vergent,

Map or regional volume?

Wipneus may be the best bet for a map, since I re-wrote my code to tidy up, difference maps would need a total rewrite to get them running (it's complicated..). But regional figures I can do.

Volume and thickness, for May average, difference between 2012 and 2015 = 2015 - 2012.
Also for context 2012 volume for May and the percent change.

Volume in km^3.
   Difference / 2012 Vol / %  Change
Other   0.0   0.0   0.00%
Okhotsk   -42.2   108.2   -39.03%
Bering   -221.7   261.3   -84.84%
Beaufort   -257.9   1098.1   -23.49%
Chukchi   -238.0   1394.9   -17.06%
ESS   -149.2   2032.3   -7.34%
Laptev   -0.6   1049.1   -0.06%
Kara   242.4   624.5   38.82%
Barents   176.0   193.2   91.13%
Greenland   -62.0   650.4   -9.53%
Central   1535.1   10557.6   14.54%
CAA    54.0   1473.8   3.67%
Baffin   184.3   962.3   19.15%
Hudson   83.6   1309.0   6.39%
All   1303.9   21714.7   6.00%
Arctic Ocean   1299.9   19073.9   6.81%


Thickness in metres.         
   Difference / 2012 Vol / %  Change
Other   0.00   0   0.00%
Okhotsk   -0.16   0.63   -25.25%
Bering   -0.28   0.49   -56.85%
Beaufort   -0.48   2.11   -22.50%
Chukchi   -0.40   2.39   -16.77%
ESS   -0.17   2.28   -7.34%
Laptev   0.00   1.64   -0.06%
Kara   0.28   0.83   34.33%
Barents   0.31   0.63   49.90%
Greenland   0.04   0.82   4.52%
Central   0.35   2.38   14.54%
CAA   0.07   1.95   3.67%
Baffin   0.17   0.92   18.38%
Hudson   0.08   1.14   6.90%
All   0.17   1.74   9.63%
Arctic Ocean   0.13   1.98   6.79%

Hope that's of use.

PS Beaufort is the thinnest and lowest volume on record!

ChrisReynolds

Thanks! Maps would be more intuitive, and answer questions like; "is the thickness difference in the CAB bunched along the CAA?"

Verg


Wipneus

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Re: Latest PIOMAS update (July)
« Reply #604 on: July 03, 2015, 02:15:03 PM »
PIOMAS gridded data was updated (still waiting for the main daily data and graphs).

Here are the maps with monthly average thickness of June 2014, 2015 as well as the difference.


Wipneus

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Re: Latest PIOMAS update (July)
« Reply #605 on: July 03, 2015, 02:16:57 PM »
And difference in growth from May to June,  red means more thickening/less thinning.

Wipneus

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Re: Latest PIOMAS update (July)
« Reply #606 on: July 03, 2015, 02:58:19 PM »
Previous two posts are monthly average.
More interesting are of course the daily files, here is an animation of the June melt.

(click req'd)

Wipneus

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Re: Latest PIOMAS update (July)
« Reply #607 on: July 03, 2015, 04:08:29 PM »
For the curious, here are the monthly volumes derived from gridded daily data for June 30. May be slightly different from the real daily data.
It seems 2015 is still in sixth place, but coming closer...
   year    vol
1  2000 21.044
2  2001 21.074
3  2002 20.672
4  2003 20.071
5  2004 19.916
6  2005 18.564
7  2006 17.930
8  2007 15.594
9  2008 17.443
10 2009 16.564
11 2010 13.458
12 2011 12.917
13 2012 12.295
14 2013 14.041
15 2014 14.642
16 2015 15.263

Nightvid Cole

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Re: Latest PIOMAS update (July)
« Reply #608 on: July 03, 2015, 06:15:22 PM »
It is absolutely, positively weird just how thick PIOMAS thinks the ice off the CAA and Greenland have now become. If we are to believe it, that ice has gone from ~2.5 m in 2012 to > 4 m in 2015. This is a 70% increase in thickness!

What's even stranger still is that PIOMAS seems to have started seriously straying away from anything with a semblance of reality - the buoys on the Pacific side of the CAB are unanimous in telling us that this ice did not get above 2 - 2.05 m in thickness this past winter, and most of them topped out at only around 1.75 m. Yet PIOMAS thinks it got up to almost 2.5 m.

Also, TOPAZ4 seems to agree with Cryosat as well as ADS/VISHOP in telling us that the thick ice of 2014 on the CAA side of the Arctic had in fact moderated in thickness this year in winter and in spring. Quite to the contrary, PIOMAS is saying that this ice got even thicker, for a third straight year!!!

I am truly surprised by this. PIOMAS seemed to be a good model, or so I thought. Now it basically has gone its own way and is disagreeing with every other model and observation. Why????


Neven

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Re: Latest PIOMAS update (July)
« Reply #609 on: July 03, 2015, 07:11:14 PM »
I am truly surprised by this. PIOMAS seemed to be a good model, or so I thought. Now it basically has gone its own way and is disagreeing with every other model and observation. Why????

Don't draw conclusions too fast.
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Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #610 on: July 03, 2015, 07:25:06 PM »
Are there obvious differences between any reliable observations of thickness and the PIOMAS representation?

I am also a little confused about what is meant by "thickness" - regarding sea ice data, does this normally refer to the average thickness of the ice over the ice-covered area? That would be a useful definition, but I wonder which data sources are capable of measuring that. Particularly when discussing the type of heterogeneous rubble that is Beaufort, "thickness" can be a complicated property to represent in a single number.

Richard Rathbone

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Re: Latest PIOMAS update (July)
« Reply #611 on: July 03, 2015, 07:45:39 PM »
Wipneus' numbers give a bit more melt in June 2015 than 2014 or 2013, which is what would would be expected from May's melt ponds as assessed by Schroeder. The same sort of excess over 2014 for the rest of the season will bring 2015 volume close to or slightly below 2014 volume around the minimum.

Steven

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Re: Latest PIOMAS update (July)
« Reply #612 on: July 03, 2015, 08:20:51 PM »
It is absolutely, positively weird just how thick PIOMAS thinks the ice off the CAA and Greenland have now become. If we are to believe it, that ice has gone from ~2.5 m in 2012 to > 4 m in 2015. This is a 70% increase in thickness!

What's even stranger still is that PIOMAS seems to have started seriously straying away from anything with a semblance of reality - the buoys on the Pacific side of the CAB are unanimous in telling us that this ice did not get above 2 - 2.05 m in thickness this past winter, and most of them topped out at only around 1.75 m. Yet PIOMAS thinks it got up to almost 2.5 m.

Also, TOPAZ4 seems to agree with Cryosat as well as ADS/VISHOP in telling us that the thick ice of 2014 on the CAA side of the Arctic had in fact moderated in thickness this year in winter and in spring. Quite to the contrary, PIOMAS is saying that this ice got even thicker, for a third straight year!!!

I am truly surprised by this. PIOMAS seemed to be a good model, or so I thought. Now it basically has gone its own way and is disagreeing with every other model and observation. Why????

A few weeks ago I had a look at the IceBridge QuickLook data, which can be downloaded at this page.  These data confirm that the sea ice north of the CAA was thicker in March 2015 than in preceding years.  Moreover, the same is true for the sea ice in Eastern Beaufort Sea.  That seems to be in good agreement with PIOMAS.

Regarding Cryosat, this recent paper by Ricker et al. 2015 may be relevant.  The paper suggest that Cryosat overestimated the sea ice freeboard and thickness north of the CAA during the 2013/2014 freezing season, due to snow backscatter of the radar signal.  Here are the concluding paragraphs of the Ricker et al. paper (see especially the first one):

Quote
An exceptional high snow depth and early accumulation during the freezing season 2013/2014 north of Canada, shown by IMB measurements and indicated by Operation IceBridge snow depth retrievals, might have lead to the major increase of CryoSat-2 multiyear ice freeboard in November 2013 for this region. By quantifying the impact on CryoSat-2 sea ice thickness retrievals, we obtain a mean multiyear ice thickness bias of 1.4 m, if it is assumed that the main scattering horizon is given by the snow-ice interface.

We conclude that snowfall can have a significant impact on CryoSat-2 range measurements and therefore on ice freeboard, thickness, and volume. The assumption that the CryoSat-2 main scattering horizon is given by the snow-ice interface cannot be justified in regions with a thick snow layer. Finally, this study also shows that there is a strong need for more data and knowledge about the seasonal cycle of snow distribution and properties on sea ice.

seaicesailor

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Re: Latest PIOMAS update (July)
« Reply #613 on: July 03, 2015, 08:47:31 PM »
Actually the animation confirms the 1 m thinning of the ice from Beaufort to Laptev and part of the CAB. So no surprise about something I still dont understand. What caused such thinning in this particular June month? Storms?

In Beaufort the av thickness is about or less than 1m, but because of open water, the MYI floes probably are 1.5 to 2 m thick.

Nightvid Cole

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Re: Latest PIOMAS update (July)
« Reply #614 on: July 03, 2015, 08:53:46 PM »
It is absolutely, positively weird just how thick PIOMAS thinks the ice off the CAA and Greenland have now become. If we are to believe it, that ice has gone from ~2.5 m in 2012 to > 4 m in 2015. This is a 70% increase in thickness!

What's even stranger still is that PIOMAS seems to have started seriously straying away from anything with a semblance of reality - the buoys on the Pacific side of the CAB are unanimous in telling us that this ice did not get above 2 - 2.05 m in thickness this past winter, and most of them topped out at only around 1.75 m. Yet PIOMAS thinks it got up to almost 2.5 m.

Also, TOPAZ4 seems to agree with Cryosat as well as ADS/VISHOP in telling us that the thick ice of 2014 on the CAA side of the Arctic had in fact moderated in thickness this year in winter and in spring. Quite to the contrary, PIOMAS is saying that this ice got even thicker, for a third straight year!!!

I am truly surprised by this. PIOMAS seemed to be a good model, or so I thought. Now it basically has gone its own way and is disagreeing with every other model and observation. Why????

A few weeks ago I had a look at the IceBridge QuickLook data, which can be downloaded at this page.  These data confirm that the sea ice north of the CAA was thicker in March 2015 than in preceding years.  Moreover, the same is true for the sea ice in Eastern Beaufort Sea.  That seems to be in good agreement with PIOMAS.

Regarding Cryosat, this recent paper by Ricker et al. 2015 may be relevant.  The paper suggest that Cryosat overestimated the sea ice freeboard and thickness north of the CAA during the 2013/2014 freezing season, due to snow backscatter of the radar signal.  Here are the concluding paragraphs of the Ricker et al. paper (see especially the first one):

Quote
An exceptional high snow depth and early accumulation during the freezing season 2013/2014 north of Canada, shown by IMB measurements and indicated by Operation IceBridge snow depth retrievals, might have lead to the major increase of CryoSat-2 multiyear ice freeboard in November 2013 for this region. By quantifying the impact on CryoSat-2 sea ice thickness retrievals, we obtain a mean multiyear ice thickness bias of 1.4 m, if it is assumed that the main scattering horizon is given by the snow-ice interface.

We conclude that snowfall can have a significant impact on CryoSat-2 range measurements and therefore on ice freeboard, thickness, and volume. The assumption that the CryoSat-2 main scattering horizon is given by the snow-ice interface cannot be justified in regions with a thick snow layer. Finally, this study also shows that there is a strong need for more data and knowledge about the seasonal cycle of snow distribution and properties on sea ice.

Thanks - the Ricker et al. paper was quite interesting, and does explain a lot. It also seems unsurprising in light of the fact that it seems that microwaves' penetrating power of lots of things seems to often be overstated - yet in reality, even light things scatter and block microwaves quite a bit. The same phenomenon probably accounts for why clouds block the passive microwave data so easily, why bad weather interrupts satellite TV, and cell phone signals get cut out so easily. In all these cases, it seems the assumption (though incorrect) is that dielectrics are transparent, even though in reality they are not - as observation demonstrates.

However, this still does not solve the paradox of why TOPAZ4 and PIOMAS get such dramatically different answers, nor does it explain why PIOMAS disagrees with the buoy observations about ice thickness in the Beaufort/Chukchi sector of the CAB.


Lord M Vader

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Re: Latest PIOMAS update (July)
« Reply #615 on: July 03, 2015, 09:04:29 PM »
Wipneus: do you have an opportunity to make a schematic map of the difference in sea ice thickness for the period June 1- June 30? Would be very interesting to see it black and white how much thinner the ice have been in the different regions.

Best, LMV

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #616 on: July 03, 2015, 11:05:47 PM »
Actually the animation confirms the 1 m thinning of the ice from Beaufort to Laptev and part of the CAB. So no surprise about something I still dont understand. What caused such thinning in this particular June month? Storms?

In Beaufort the av thickness is about or less than 1m, but because of open water, the MYI floes probably are 1.5 to 2 m thick.

If the PIOMAS sub grid thickness distribution is right (it probably is more or less) then here are the June GICE sub grid thickness distributions for post 2010 years in Beaufort. So for example, the thickness band centred on 20.62m thick has a volume of 12.78km^3, this is intended to represent the bands of ridged ice in pressure ridges across the pack.

Thickness   2010   2011   2012   2013   2014   2015
0m   0.00   0.00   0.00   0.00   0.00   0.00
0.26m   16.43   19.59   13.77   11.52   18.25   14.34
0.71m   36.53   3.62   5.80   10.43   26.04   22.26
1.46m   110.35   94.96   74.72   197.02   147.39   108.75
2.61m   126.56   268.06   184.41   340.86   201.56   173.55
4.23m   64.11   139.46   115.87   180.58   98.31   104.71
6.39m   30.05   47.07   39.45   73.73   40.41   42.82
9.1m   26.82   38.47   26.54   69.89   32.41   36.58
12.39m   26.98   42.87   28.50   78.66   32.39   39.20
16.24m   26.90   45.16   28.44   80.30   30.86   39.79
20.62m   8.27   18.05   7.37   21.16   4.45   12.78
25.49m   2.96   5.90   2.39   6.85   1.29   4.30

This also answers the concerns about PIOMAS disagreeing with one point in a million km^2 area (519000km^2 for Beaufort, 584000km^2 for Chukchi). What you see in Wipneus's plots is the grid box effective thickness. The relationship between the effective thickness and the sub grid thickness distributions is explained here:
http://dosbat.blogspot.co.uk/2015/04/what-is-piomas-gice.html

There is no discrepancy between PIOMAS and the single points from bouys, this issue is why point data like Buoys were not used in the Schweiger et al 2011 intercomparison study. Moored ULS sounders were used, but they are fixed to the sea ice, and sea ice movement can present the range of actual thickness.

PIOMAS has a bias: From Schweiger et al 2011 "PIOMAS appears to overestimate thin ice thickness and underestimate thick ice, yielding a smaller downward trend than apparent in reconstructions from observations."

PIOMAS gain since June 2012.

slow wing

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Re: Latest PIOMAS update (July)
« Reply #617 on: July 04, 2015, 12:52:11 AM »
Regarding Nightvid Cole's & Steven's posts, a quick comparison shows PIOMAS might have been a little thicker in the Chukchi & Beaufort than CryoSat actually measured, when compared for May 2015. (Cryosat couldn't measure any later in the Summer due to melt ponds.)

Wipneus posted the May PIOMAS thickness reconstruction here...
http://forum.arctic-sea-ice.net/index.php/topic,119.msg53274.html#msg53274

While the roughly corresponding map from CryoSat is here...
http://www.cpom.ucl.ac.uk/csopr/seaice.html

Probably the best comparison is to click on "14 days", which shows 5-19 May for Cryosat.

The Chukchi Sea for that plot is, very roughly speaking, mostly a mix of green & yellow areas, which is, respectively, the 1.75-2.00m and 2.00-2.25 m thickness bins.
So the average looks about 2m.

For comparison, PIOMAS in the same region shows mostly the 2.00-2.25 bins, with some thicker but little in the yellow 1.75-2.00m thickness bin.


So, at first glance, PIOMAS looked slightly thicker there than the CryoSat measurements, perhaps by of order 10%. This is hardly surprising given the model and measurement uncertainties.


That was just a quick eyeball comparison. I'm sure the scientists themselves have done a more thorough comparison.

Nightvid Cole

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Re: Latest PIOMAS update (July)
« Reply #618 on: July 04, 2015, 01:57:18 AM »
Actually the animation confirms the 1 m thinning of the ice from Beaufort to Laptev and part of the CAB. So no surprise about something I still dont understand. What caused such thinning in this particular June month? Storms?

In Beaufort the av thickness is about or less than 1m, but because of open water, the MYI floes probably are 1.5 to 2 m thick.

If the PIOMAS sub grid thickness distribution is right (it probably is more or less) then here are the June GICE sub grid thickness distributions for post 2010 years in Beaufort. So for example, the thickness band centred on 20.62m thick has a volume of 12.78km^3, this is intended to represent the bands of ridged ice in pressure ridges across the pack.

Thickness   2010   2011   2012   2013   2014   2015
0m   0.00   0.00   0.00   0.00   0.00   0.00
0.26m   16.43   19.59   13.77   11.52   18.25   14.34
0.71m   36.53   3.62   5.80   10.43   26.04   22.26
1.46m   110.35   94.96   74.72   197.02   147.39   108.75
2.61m   126.56   268.06   184.41   340.86   201.56   173.55
4.23m   64.11   139.46   115.87   180.58   98.31   104.71
6.39m   30.05   47.07   39.45   73.73   40.41   42.82
9.1m   26.82   38.47   26.54   69.89   32.41   36.58
12.39m   26.98   42.87   28.50   78.66   32.39   39.20
16.24m   26.90   45.16   28.44   80.30   30.86   39.79
20.62m   8.27   18.05   7.37   21.16   4.45   12.78
25.49m   2.96   5.90   2.39   6.85   1.29   4.30

This also answers the concerns about PIOMAS disagreeing with one point in a million km^2 area (519000km^2 for Beaufort, 584000km^2 for Chukchi). What you see in Wipneus's plots is the grid box effective thickness. The relationship between the effective thickness and the sub grid thickness distributions is explained here:
http://dosbat.blogspot.co.uk/2015/04/what-is-piomas-gice.html

There is no discrepancy between PIOMAS and the single points from bouys, this issue is why point data like Buoys were not used in the Schweiger et al 2011 intercomparison study. Moored ULS sounders were used, but they are fixed to the sea ice, and sea ice movement can present the range of actual thickness.

PIOMAS has a bias: From Schweiger et al 2011 "PIOMAS appears to overestimate thin ice thickness and underestimate thick ice, yielding a smaller downward trend than apparent in reconstructions from observations."

PIOMAS gain since June 2012.


Ok, this makes sense. One minor quibble - the 0.000m thickness band is obviously only those with thicknesses less than or equal to 0.00m - otherwise the volume would not be zero. It is *not* a band centered on 0.00m.

So I'd assume that, likewise, "0.26m" is thicknesses UP TO 0.26m, not "centered on" 0.26m, and so on. Right?

oren

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Re: Latest PIOMAS update (July)
« Reply #619 on: July 04, 2015, 06:24:04 AM »
Ok, this makes sense. One minor quibble - the 0.000m thickness band is obviously only those with thicknesses less than or equal to 0.00m - otherwise the volume would not be zero. It is *not* a band centered on 0.00m.

So I'd assume that, likewise, "0.26m" is thicknesses UP TO 0.26m, not "centered on" 0.26m, and so on. Right?

My wild uneducated guess, just by looking at the numbers, is that 0.26 is a band of 0.01-0.50, 0.71 is 0.51 to 1.00, and then 1-2, 2-3, 3-5 etc.
0.00 is a band of 0.00-0.00

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Re: Latest PIOMAS update (July)
« Reply #620 on: July 04, 2015, 08:21:19 AM »
Nightvid, Oren,

The bands are given in my post on PIOMAS Gice, from the paper by Dr Zhang, they're shown in the image below.

Nightvid Cole

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Re: Latest PIOMAS update (July)
« Reply #621 on: July 04, 2015, 01:55:41 PM »
Nightvid, Oren,

The bands are given in my post on PIOMAS Gice, from the paper by Dr Zhang, they're shown in the image below.


Since negative thicknesses are physically nonsensical, shouldn't you use 0.05 as the thickness to calculate the volume of the "0" band, since it represents thicknesses from -0.1 to 0.1 and thus physically must be 0 to 0.1, with a middle of 0.05?

In other words, volume = area * 0.05, not area * 0?

OR, alternatively, would this lead to the entire open water portion of the domain making a spurious contribution to the volume?

Is there any distinction between "real" zero and "very very thin" ice?

Tor Bejnar

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Re: Latest PIOMAS update (July)
« Reply #622 on: July 04, 2015, 01:57:34 PM »
So why does the 0m band (that includes ice up to 0.10 m thick) always have 0.00 volume? 

Assuming an actual average thickness of 0.05 m (5 cm or 5x10-5 km), it would required 200 km2 to reach a volume of 0.01 km3. (It could be almost half this area and round to 0.01 km3.)  The least volume recorded, 1.29 km3 averages 25.49 m (or 0.02549 km)[assuming equal distribution across its thickness] covers only 50.6 km2.
Arctic ice is healthy for children and other living things.

oren

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Re: Latest PIOMAS update (July)
« Reply #623 on: July 04, 2015, 05:18:58 PM »
Nightvid, Oren,

The bands are given in my post on PIOMAS Gice, from the paper by Dr Zhang, they're shown in the image below.


Thanks Chris.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #624 on: July 04, 2015, 05:23:56 PM »
Mathematically the zero thickness band needs upper and lower limits, those limits have been chosen as shown. Zero thickness band is open water, not very thin ice, this is by definition. The bands are bands of thickness within the grid box upon which the equation set of the model operates, moving ice volume up and down through the bands according to the modelled processes.

When you take grid box effective thickness the situation is different, a gbet if 0.1m may indeed represent dispersed ice, which in theory could be thick chunks in a lot of open water.

Typing on a very bouncy bus! Hope I make sense.

PS just occurred to me that if lower limit of zero band were zero exactly ut might make the equations crash.

Peter Ellis

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Re: Latest PIOMAS update (July)
« Reply #625 on: July 04, 2015, 07:08:28 PM »
Right, so if I understand it right.

1) The lowest band in the model represents open water
2) That band therefore has to have a _central_ value of zero
3) A band can't have zero width

Therefore, they've chosen +10cm as being effectively negligible, i.e. everything less than 10cm counts as zero / open water. The -10 cm lower limit of the band is simply a mathematical trick to enforce the real rule, which is "treat everything lower than 10cm as open water / zero ice".

Andreas T

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Re: Latest PIOMAS update (July)
« Reply #626 on: July 04, 2015, 08:09:49 PM »
Couldn't  the question whether the band named "0.0m" has no ice in it because at this time of the year thin ice has melted away or it is by definition a band of 0 volume  be answered by looking at October or November when one can expect substantial areas of ice between 0 and 0.1m thick? I don't know where to look though.

Tor Bejnar

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Re: Latest PIOMAS update (July)
« Reply #627 on: July 04, 2015, 08:33:31 PM »
Thanks again Chris and Peter, too!  Those pesky infinities and undefined functions.  :)
Arctic ice is healthy for children and other living things.

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Re: Latest PIOMAS update (July)
« Reply #628 on: July 04, 2015, 10:42:10 PM »
Mathematically the zero thickness band needs upper and lower limits, those limits have been chosen as shown. Zero thickness band is open water, not very thin ice, this is by definition.

No, "open water" is a thickness of precisely 0, not a thickness of < 0.1m!!!

The bands are bands of thickness within the grid box upon which the equation set of the model operates, moving ice volume up and down through the bands according to the modelled processes.

When you take grid box effective thickness the situation is different, a gbet if 0.1m may indeed represent dispersed ice, which in theory could be thick chunks in a lot of open water.

Typing on a very bouncy bus! Hope I make sense.

PS just occurred to me that if lower limit of zero band were zero exactly ut might make the equations crash.

I don't get it. What happens when ice first "grows" from zero thickness? There is necessarily a time when it is not zero, but is less than 0.1m. How is this handled by the model?

Andreas T

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Re: Latest PIOMAS update (July)
« Reply #629 on: July 05, 2015, 04:36:44 AM »
Mathematically the zero thickness band needs upper and lower limits, those limits have been chosen as shown. Zero thickness band is open water, not very thin ice, this is by definition.

No, "open water" is a thickness of precisely 0, not a thickness of < 0.1m!!!

The bands are bands of thickness within the grid box upon which the equation set of the model operates, moving ice volume up and down through the bands according to the modelled processes.

...........

I don't get it. What happens when ice first "grows" from zero thickness? There is necessarily a time when it is not zero, but is less than 0.1m. How is this handled by the model?
having had a look at http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%282003%29131%3C0845%3AMGSIWA%3E2.0.CO%3B2 I think I understand what Chris is saying.
The model approximates the range of ice thickness in a grid cell by a set of 12 thickness "bins". That means when water freezes the 0.0m bin becomes less full and the 0.26m bin becomes fuller, there just are no thickness values in between. Thickening through freezing or compaction / ridging moves ice from the 0.26m bin to the 0.71m bin and so on. This is the usual way for treating a continuous variable in discrete steps in numerical models.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #630 on: July 05, 2015, 09:25:08 AM »
Peter, exactly right.

Mathematically the zero thickness band needs upper and lower limits, those limits have been chosen as shown. Zero thickness band is open water, not very thin ice, this is by definition.

No, "open water" is a thickness of precisely 0, not a thickness of < 0.1m!!!

The bands are bands of thickness within the grid box upon which the equation set of the model operates, moving ice volume up and down through the bands according to the modelled processes.

...........

I don't get it. What happens when ice first "grows" from zero thickness? There is necessarily a time when it is not zero, but is less than 0.1m. How is this handled by the model?
having had a look at http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%282003%29131%3C0845%3AMGSIWA%3E2.0.CO%3B2 I think I understand what Chris is saying.
The model approximates the range of ice thickness in a grid cell by a set of 12 thickness "bins". That means when water freezes the 0.0m bin becomes less full and the 0.26m bin becomes fuller, there just are no thickness values in between. Thickening through freezing or compaction / ridging moves ice from the 0.26m bin to the 0.71m bin and so on. This is the usual way for treating a continuous variable in discrete steps in numerical models.

Yes, you are right. The equation set behind PIOMAS will create a continuous (not banded) distribution of thickness change, after each iteration of the model's equations there is a process of setting the resultant new thicknesses into the new band. I guess that during summer as ice melts the downward movement of thickness dumps more area into the open water band, before allocating things like rounding errors may produce slightly negative thickness, this would then be reset to zero.

****

Rather than look at it in terms of volume, perhaps it would be best to look at area of each band.

In the following I have summed to bands, OW is open water (0m thickness), <3.3m is the sum of the 0.26m to 2.61m bands, >3.3m is the sum of the 4.23 to 25.49m bands. I have chosen the Central Arctic.

First here is the annual cycle for the year 2000, a year chosen randomly as a year before the post 2007 changes. OW is open water

Annual         
___   OW   <3.3m   >3.3m
Jan   0.059   3.541   0.828
Feb   0.040   3.479   0.908
Mar   0.039   3.393   0.995
Apr   0.039   3.306   1.082
May   0.083   3.196   1.149
Jun   0.260   3.002   1.166
Jul   0.567   2.862   0.998
Aug   0.678   2.917   0.833
Sep   0.391   3.255   0.782
Oct   0.198   3.461   0.769
Nov   0.116   3.555   0.757
Dec   0.071   3.567   0.789

The figures are area in million kmsq. So in April 0.039 million kmsq is open water, 3.306million kmsq has ice less than 3.3m thick, 1.082 has ice over 3.3m thick. So even in April for the PIOMAS model there is about 0.9% open water (0.039 million kmsq) within the Central Arctic. In 2000 the peak open water was in August at 15% of the total area of the Central Arctic.

Turning to September the areas of the two thickness bands and open water (OW) are tabled below.

September         
___   OW   <3.3m   >3.3m
1979   0.433   2.884   1.111
1980   0.221   3.114   1.092
1981   0.334   3.246   0.848
1982   0.276   3.295   0.856
1983   0.354   3.089   0.984
1984   0.511   2.928   0.988
1985   0.473   3.032   0.923
1986   0.302   3.019   1.108
1987   0.228   3.122   1.078
1988   0.263   3.118   1.046
1989   0.276   3.071   1.080
1990   0.454   2.950   1.023
1991   0.445   3.067   0.915
1992   0.276   3.097   1.055
1993   0.387   3.096   0.945
1994   0.320   3.111   0.997
1995   0.485   3.137   0.806
1996   0.370   3.158   0.899
1997   0.280   3.180   0.968
1998   0.585   3.057   0.785
1999   0.522   3.169   0.737
2000   0.391   3.255   0.782
2001   0.477   3.133   0.818
2002   0.470   3.134   0.824
2003   0.516   3.158   0.754
2004   0.568   3.224   0.635
2005   0.583   3.216   0.628
2006   0.506   3.336   0.585
2007   1.598   2.357   0.472
2008   1.242   2.655   0.531
2009   1.252   2.669   0.507
2010   1.578   2.539   0.310
2011   1.575   2.562   0.291
2012   2.275   1.882   0.270
2013   1.331   2.773   0.323
2014   1.275   2.670   0.482

Look at what happened in 2007!

PIOMAS is adjusted by concentration from NSIDC, the same data used to make NSIDC extent and area. That noted, as an 'idiot check' I have scatter plotted PIOMAS fraction of open water in the Central Arctic, and NSIDC September average Area divided by March 1981 to 2010 average extent as the open water fraction for NSIDC. This is attached as a graphic.


Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #631 on: July 05, 2015, 02:33:09 PM »
If the PIOMAS sub grid thickness distribution is right (it probably is more or less) then here are the June GICE sub grid thickness distributions for post 2010 years in Beaufort. So for example, the thickness band centred on 20.62m thick has a volume of 12.78km^3, this is intended to represent the bands of ridged ice in pressure ridges across the pack.

Thickness   2010   2011   2012   2013   2014   2015
0m   0.00   0.00   0.00   0.00   0.00   0.00
0.26m   16.43   19.59   13.77   11.52   18.25   14.34
0.71m   36.53   3.62   5.80   10.43   26.04   22.26
. . .

Chris, does this data set represent an average for the full month of June, or the month-end values? If not month-end, is that available?

Thanks

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #632 on: July 05, 2015, 10:50:34 PM »
Nick,

It's all June average. I have some bare bones code to handle the daily data, but as that only goes back to 2000 I don't normally bother with it. I'll post some figures for the end of the month if needed (for Beaufort?).

If I haven't done so by this time Tuesday, PM me to prompt me.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #633 on: July 06, 2015, 06:47:45 PM »
Nick, I have all the data for Gice sub grid volumes from 2007 to 2015 30 June.

For example, here is...

Peripheral Seas (Beaufort, Chukchi, ESS, Laptev)
   <3.3m   >3.3m
2007   1426.1   916.3
2008   2019.8   1270.0
2009   1747.3   1055.5
2010   1474.1   1826.7
2011   1476.6   847.2
2012   1476.4   1113.7
2013   1791.1   1513.8
2014   1515.8   803.7
2015   1663.8   1023.6

Central Arctic.
   <3.3m   >3.3m
2007   4768.0   4604.9
2008   5005.2   4455.0
2009   5283.1   4354.1
2010   4365.4   3475.3
2011   4662.7   3763.1
2012   4529.6   3805.1
2013   4971.8   3711.7
2014   5326.4   4744.5
2015   4516.3   5494.0

Regions as per Cryosphere Today, volumes in 1000km^3.

Last year had a lower volume of thick ice in peripheral seas. This year is a bit lower than 2012.

Here are the numbers for Beaufort.

   >3.3m   <3.3m   Total
2007   0.273   0.194   0.467
2008   0.151   0.143   0.293
2009   0.266   0.160   0.427
2010   0.154   0.100   0.254
2011   0.243   0.234   0.477
2012   0.150   0.133   0.283
2013   0.446   0.447   0.893
2014   0.211   0.146   0.357
2015   0.236   0.234   0.470

2012 was much lower, but really the excitement this year is in Chukchi, ESS, and Laptev.

Although I said I doubt we'll get near 2012 this year, and that remains my formal position. I am allowing myself to get a bit excited about the state in Chukchi, ESS and Laptev.  ;D

Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #634 on: July 06, 2015, 08:28:45 PM »
Thanks Chris. Is the Beaufort data scaled differently?

Also, do you have a link to the raw data, assuming it's publicly available?

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #635 on: July 06, 2015, 08:52:24 PM »
Yes, sorry, I'm not properly set up with this and the sheet is a messy hotch potch reflecting me messing around with the data. The Beaufort data is thousand km^3. This does not impact the other Peripheral Seas or Central Arctic data.

I've uploaded the tabulated raw data here, I have also tagged on the 31 May data.

https://drive.google.com/file/d/0B3pB-kdzoLU3NHRLU3JENFVtbXc/view?usp=sharing

I'll keep it there for a few days.

I caution, I have not really been using this data, it should be correct as I use the same core code to generate as for the monthly data - but I have not properly checked it nor have I used in such a way that problems would become apparent. The main check would be comparison with the PIOMAS main series of volume, but I just haven't had the time to do that.

So it is provided 'without warranty', so to speak. But I wouldn't post it if I wasn't happy to use it myself for my own purposes.

seaicesailor

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Re: Latest PIOMAS update (July)
« Reply #636 on: July 06, 2015, 09:14:33 PM »
Nick, I have all the data for Gice sub grid volumes from 2007 to 2015 30 June.

For example, here is...

Peripheral Seas (Beaufort, Chukchi, ESS, Laptev)
   <3.3m   >3.3m
2007   1426.1   916.3
2008   2019.8   1270.0
2009   1747.3   1055.5
2010   1474.1   1826.7
2011   1476.6   847.2
2012   1476.4   1113.7
2013   1791.1   1513.8
2014   1515.8   803.7
2015   1663.8   1023.6

Central Arctic.
   <3.3m   >3.3m
2007   4768.0   4604.9
2008   5005.2   4455.0
2009   5283.1   4354.1
2010   4365.4   3475.3
2011   4662.7   3763.1
2012   4529.6   3805.1
2013   4971.8   3711.7
2014   5326.4   4744.5
2015   4516.3   5494.0

Regions as per Cryosphere Today, volumes in 1000km^3.

Last year had a lower volume of thick ice in peripheral seas.

Evaluate something by eyeballing a map can be just very wrong . Thank you for these computations.


ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #637 on: July 06, 2015, 09:32:01 PM »
This also has the advantage of giving you the picture from within the model, not just grid box effective area. But I haven't a clue how to practically give this data in map form, unless I use 12 images as an animated gif - which is a lot of work for me.

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Re: Latest PIOMAS update (July)
« Reply #638 on: July 07, 2015, 07:05:22 PM »
The official PIOMAS update is there as well. I have updated my graphs, you can see them in the top post

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Re: Latest PIOMAS update (July)
« Reply #639 on: July 07, 2015, 07:18:17 PM »
The official PIOMAS update is there as well. I have updated my graphs, you can see them in the top post

Thanks, wip!
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epiphyte

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Re: Latest PIOMAS update (July)
« Reply #640 on: July 08, 2015, 06:47:21 AM »
I just want to ping everyone on something I brought up in early March, just before the PIOMAS Feb numbers came out. At that time I said that PIOMAS Feb-April volume increase was very likely to be greater than last year, even if freezing conditions turned out to be crappy throughout.

In the event freezing conditions did appear to be awfully bad, and PIOMAS volume growth was indeed unusually high.  As I outlined at the time (reasoning cut-and-pasted below) the error was already baked-in, and IMO the only question now is whether things get bad enough to directly observe that this was the case...

Quote
Flawed as I believe PIOMAS to be for thin/melting ice, for trends I would have guessed that adding the extra dimension might filter out some of the noise from variations in here-today, gone-tomorrow start/end of season weather conditions. Others have suggested that these effects make area/extent on it's own useless as a predictor of what's going to happen later on in the season - and I'd generally agree.

But eyeballing those PIOMAS monthly trends it seems to me that there's been something very odd going over the past year... either with the model, or with the real world, or both... Viz:

1. The trends for March and May crossed in 2009. Before then, there was consistently more ice in May than in March, since then there has consistently been less ice in May than there was in March - including last year, which was well above the trend for both months.

2. According to PIOMAS there has since 2009 been a consistent 1M km3 volume gain Mar-Apr , and it has always been lost Apr-May, again regardless of trend.

3. Backing up to January , and roughly eyeballing the graph, PIOMAS has never come up with a Jan-Feb volume increase of less than ~2.5 Mkm3, or a Feb-Mar increase less than ~2Mkm3

So if PIOMAS stays true to form, the Feb number will be >= 21M, and under better-than-existing worst case conditions the the March number will be >= 23M and the April number will be >= 24M

In other words, the January number is high enough to guarantee that the April number will be more than a million km3 *higher* than it was in 2014, absent worse than existing worst-case behavior in February and March.

So we just lived through Feb - and to my eyes at least it looked as though it might indeed have have been the worst ever. Assume that PIOMAS cuts it's previous worst-case Feb growth in half (i.e. from ~2.5 to ~1.25m). If it did that the Feb number would be the same as it was last year.

Looking at the actual area today it is essentially the same as it was this time last year - so If PIOMAS does come up with a 50% cut in Feb volume growth over 2014 (which itself was very low),  it might be a plausible number - albeit an unprecedentedly bad February for the arctic -  but only if the avg. thickness is also now the same as this time last year. This seems a stretch given the weak winter and the low thickness estimates. If the ice is actually thinner, then PIOMAS would need essentially zero Feb growth to avoid coming up with an incredible number for Apr/May.

If, OTOH, PIOMAS comes in with the same (already low) Feb & Mar growth that it did in 2014, it can only end with a modeled March-May volume >1m km3 higher than it was last year, which would IMO be astonishing if true, because it would imply faster Feb growth than 2014, on top of thicker ice than 2014, in the presence of higher temperatures than 2014.

So all in all, I'm wondering if this might be the year when PIOMAS last-meter uncertainties finally cause it to part company with directly observable reality.

Looking back over the past four months, I haven't yet seen anything to disabuse me of any of the above...




iwantatr8

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Re: Latest PIOMAS update (July)
« Reply #641 on: July 08, 2015, 12:29:53 PM »
Following Chris's useful data I thought I would try to come up with a way to represent it graphically.
I've reduced the data to 3 thickness buckets and then done a %age difference from 2007 for each different location. it produces some interesting views about how things have changed. 
Most interesting is the changing thickness in the arctic ocean where the lead up to 2012 can clearly be seen contrasting against the thickness this year.

« Last Edit: July 08, 2015, 01:23:50 PM by iwantatr8 »

Rubikscube

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Re: Latest PIOMAS update (July)
« Reply #642 on: July 08, 2015, 01:04:13 PM »
Following Chris's useful data I thought I would try to come up with a way to represent it graphically.
I've reduced the data to 3 thickness buckets and then done a %age difference from 2017 for each different location. it produces some interesting views about how things have changed. 
Most interesting is the changing thickness in the arctic ocean where the lead up to 2012 can clearly be seen contrasting against the thickness this year.

Niiiiice!

But I suppose you mean 2007 and not 2017?

iwantatr8

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Re: Latest PIOMAS update (July)
« Reply #643 on: July 08, 2015, 01:19:09 PM »
Yes indeed, my forecasting skills are not that good!

 ;D

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Re: Latest PIOMAS update (July)
« Reply #644 on: July 08, 2015, 07:34:26 PM »
Epiphyte,

Your statements are in quotes.

Quote
1. The trends for March and May crossed in 2009. Before then, there was consistently more ice in May than in March, since then there has consistently been less ice in May than there was in March - including last year, which was well above the trend for both months.


This crossing is due to the PIOMAS spring volume loss, which involves anomalous loss of volume from around 20 April to around the solstice. I shall shortly be blogging further on why this anomaly should be viewed as a result of thinning, particularly in the Central Arctic since the 2010 volume loss event.

Quote
2. According to PIOMAS there has since 2009 been a consistent 1M km3 volume gain Mar-Apr , and it has always been lost Apr-May, again regardless of trend.

Again, an effect of the PIOMAS spring volume loss anomaly, prior to 2010 the Apr-May volume loss was substantially lower.

Quote
3. Backing up to January , and roughly eyeballing the graph, PIOMAS has never come up with a Jan-Feb volume increase of less than ~2.5 Mkm3, or a Feb-Mar increase less than ~2Mkm3

So if PIOMAS stays true to form, the Feb number will be >= 21M, and under better-than-existing worst case conditions the the March number will be >= 23M and the April number will be >= 24M

Jan to Feb; The average increase is 2.74, the min is 2.23, but broadly correct. At 3.01 the 2015 jan Feb increase was above average but substantially less than the post 2012 increase of 3.52, which was driven by the thickness growth feedback.

Feb to Mar: Quite a few years were below 2Mkm^2, 1978, 1979, 1980, 1984, 1987, 1989, 1990, 1992, 1993... sorry I got bored with that list. 2015 was 1.75, not unusal. Lower September extent leads to greater growth - the growth thickness feedback again.

Quote
In other words, the January number is high enough to guarantee that the April number will be more than a million km3 *higher* than it was in 2014, absent worse than existing worst-case behavior in February and March.


Yes, it was 1.31 higher.

Quote
So we just lived through Feb - and to my eyes at least it looked as though it might indeed have have been the worst ever. Assume that PIOMAS cuts it's previous worst-case Feb growth in half (i.e. from ~2.5 to ~1.25m). If it did that the Feb number would be the same as it was last year.

Sorry, you lost me here, but February volume was 23.21, Jan Feb gain was 3.01 not unusual, Feb to Mar gain was 1.75 - towards the lower end of the distribution. 1993 (1.74), 1995 (1.52), were lower making 2015 Feb to Mar gain the third lowest on record.

Quote
Looking at the actual area today it is essentially the same as it was this time last year - so If PIOMAS does come up with a 50% cut in Feb volume growth over 2014 (which itself was very low),  it might be a plausible number - albeit an unprecedentedly bad February for the arctic -  but only if the avg. thickness is also now the same as this time last year. This seems a stretch given the weak winter and the low thickness estimates. If the ice is actually thinner, then PIOMAS would need essentially zero Feb growth to avoid coming up with an incredible number for Apr/May.

I'm sorry but I really don't get how you conclude Apr/May was/would be an 'incredible' i.e. unbelievable number. The PIOMAS April volume was as I said above 1.31 higher than in 2014, but area would be uninformative as this is concentrated in the thicker ice of the Central Arctic.

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If, OTOH, PIOMAS comes in with the same (already low) Feb & Mar growth that it did in 2014, it can only end with a modeled March-May volume >1m km3 higher than it was last year, which would IMO be astonishing if true, because it would imply faster Feb growth than 2014, on top of thicker ice than 2014, in the presence of higher temperatures than 2014.

February 2015 was colder than 2014, I have attached a difference plot, so the high volume increase from Jan to feb is to be expected.

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So all in all, I'm wondering if this might be the year when PIOMAS last-meter uncertainties finally cause it to part company with directly observable reality.

It might be that I am tired (very), but I don't see how this conclusion follows.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #645 on: July 08, 2015, 07:42:47 PM »
iwantatr8,

This is data for 30 June as posted above? And it has just dawned on me that you were successful in downloading the data - did it go smoothly?

Interesting, now to explain what you see, it can be an interesting game. How about a game of throwing the ball where the ball is a question?

If you're interested here's my first throw...

Given the regional pattern of the 2007 crash, and how advanced things were in late June, how do you interpret the high % values for the Chukchi and ESS regions in years following?

iwantatr8

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Re: Latest PIOMAS update (July)
« Reply #646 on: July 09, 2015, 09:56:20 AM »
Chris,

Yes, this is your data from above. no real issues with usage, I just had to transform the data from your nice tables into something my visualization software could handle.

As to the question, it is difficult to interpret the single day data as anything other than a comparison between years, and not a particularly indicative one at that.  The apparent conclusion is that 2007 melt started earlier in the Chukchi and ESS, which when you look at the actual data is clear.  I would say that the most interesting thing about the daily data is the ability to look at the rate of change of each of the different thickness blocks as this tells more about the overall heat input to the different regions, but I'd need more data and available time to do that. [Hat tip to Wipneus for the regional graphs]

Using the rate of change could help identify likely melt scenarios for each region, but as with any of our predictions we are at the mercy of the weather.

The question I (and I suspect most) want to know the answer to is; how will the apparent return of thicker ice in the arctic ocean affect this year's melt?

Entropy101

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Re: Latest PIOMAS update (July)
« Reply #647 on: July 09, 2015, 12:07:33 PM »

Lower September extent leads to greater growth - the growth thickness feedback again.

Why?
It is a statement that I often see, but after years of lurking still do not comprehend from an energy budget point of view.
I would expect that ice growth is mostly depending on the energy in the system. If we have a low September extent we have a lot of energy in the system that needs to get out before we can have substantial ice growth.
Same if we have a warmer than average winter. Again we have an energy system that is not favourable for ice growth.
Additional energy is also entering the Arctic in winter due to higher sea water temperatures in the gulf stream and other currents.
So why do we expect a large volume growth when we reach a low September extent if we have a energy system that is not in equilibrium and an Arctic where the average winter temperatures are increasing significantly?

Back to lurking now.....

oren

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Re: Latest PIOMAS update (July)
« Reply #648 on: July 09, 2015, 05:36:38 PM »

Lower September extent leads to greater growth - the growth thickness feedback again.

Why?
It is a statement that I often see, but after years of lurking still do not comprehend from an energy budget point of view.
I would expect that ice growth is mostly depending on the energy in the system. If we have a low September extent we have a lot of energy in the system that needs to get out before we can have substantial ice growth.
Same if we have a warmer than average winter. Again we have an energy system that is not favourable for ice growth.
Additional energy is also entering the Arctic in winter due to higher sea water temperatures in the gulf stream and other currents.
So why do we expect a large volume growth when we reach a low September extent if we have a energy system that is not in equilibrium and an Arctic where the average winter temperatures are increasing significantly?

Back to lurking now.....

In very simplified unscientific terms, since winter is cold enough and long enough, all open water in the arctic ocean basin will become ~2m first-year ice at the end of winter. So the lower the Sep extent, the higher the volume growth back to FYI cover. Doesn't mean the actual volume will be higher than the previous year, but the growth will be.

plinius

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Re: Latest PIOMAS update (July)
« Reply #649 on: July 09, 2015, 06:00:47 PM »
should point out though that this picture may go bad when there is too much loss. If you store too much heat in the ocean you might fail to develop a full winter ice cover. (so there are some claims about such a hysteresis in the sea ice cover). It all hinges on how much energy you can lose throughout the winter. Given the fact that the arctic already now has some troubles to freeze in fall, I would consider that not entirely absurd.