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Author Topic: Latest PIOMAS update (September, mid-monthly update)  (Read 1253486 times)

Wipneus

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3350 on: July 19, 2020, 11:06:00 AM »
Thanks Wipneus!🙂

Only a fourth place?! :o How far away are we from first place for the date?

PIOMAS uses sea ice area for input. NSIDC sea ice area is third/fourth lowest for the day, in contrast with extent. That still may change.

Wipneus

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3351 on: July 19, 2020, 11:07:52 AM »
Some people have good use for the updated regional data files.

daily:
https://sites.google.com/site/arctischepinguin/home/piomas/data/PIOMAS-regional.txt.gz

Wipneus

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3352 on: July 19, 2020, 11:14:29 AM »
The Fram volume export graph shows more export than the July "normal".

gandul

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3353 on: July 19, 2020, 11:24:48 AM »
It’s impossible that, with the exceptional energy input this July, we are not seeing a more dramatic drop of piomas. The model is failing right now.

oren

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Re: Latest PIOMAS update (July 2020)
« Reply #3354 on: July 19, 2020, 11:48:21 AM »
In 2-3 days we should have another PIOMAS report, thanks to the tireless Wipneus. I looked at mid-July losses of past years in the CAB (days 182 to 197 to match this year
s numbering). Many years managed to lose above 1300 km3 for the period (see table below), but none managed 1400 km3. Will 2020 be the first? Considering the persistent high pressure, clear skies and low albedo, one should expect so. Will it manage 1500 km3? Who knows,
With 2020's CAB volume lagging 562 km3 behind 2019 and 340 km3 behind 2012, this is a major chance to catch up. Otherwise, a new volume record might be very hard to achieve.

2007      -1120
2008      -1224
2009      -1330
2010      -1310
2011      -1365
2012      -1384
2013      -1296
2014        -951
2015      -1355
2016      -1351
2017      -1198
2018      -1209
2019      -1343
The CAB lost 1578 km3 in this period, blowing 2012's previous record of 1384 km3 out of the water.

Jim Hunt

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3355 on: July 19, 2020, 12:34:08 PM »
PIOMAS IS WAY OVERDONE IN THE SOUTHERN CAA.

Just wait until cryosat comes back in late September and early October. I guarantee it will be shockingly low.

Are you aware of this current "issue" with AWI level 3 gridded CryoSat-2 thickness in the CAA?

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BornFromTheVoid

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3356 on: July 19, 2020, 12:49:33 PM »
Despite remaining in roughly 4th lowest position since the last update, the gap to the lowest volume continues to shrink.



I recently joined the twitter thing, where I post more analysis, pics and animations: @Icy_Samuel

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3357 on: July 19, 2020, 01:09:56 PM »
Some regional charts split into two posts. Later I hope to post rough predictions for the minimum by region and in total.

All trends continued as they were, except for the catch up in the CAB and an apparent slowdown in the CAA (IMHO caused by artifacts in end-June NSIDC area). Beaufort and Greenland Sea still sky high, Laptev and ESS still crazy low, Chukchi and Kara still on the low side.
Click each to zoom.

p.s. I must admit I suspect PIOMAS is underestimating volume loss this period, but the numbers are what they are, this is just a layman's hunch. As PIOMAS is constrained by NSIDC data, should there be a significant melt-out in the coming two months, volume will follow accordingly.
« Last Edit: July 19, 2020, 01:16:34 PM by oren »

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3358 on: July 19, 2020, 01:10:55 PM »
4 additional charts. Click each to zoom.

Phoenix

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Re: Latest PIOMAS update (July 2020)
« Reply #3359 on: July 19, 2020, 03:24:52 PM »

The CAB lost 1578 km3 in this period, blowing 2012's previous record of 1384 km3 out of the water.

Flat out obliterated the trend. The GAAC has indeed been great.


gerontocrat

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3360 on: July 19, 2020, 06:06:41 PM »
Thanks Wipneus!🙂

Only a fourth place?! :o How far away are we from first place for the date?

PIOMAS uses sea ice area for input. NSIDC sea ice area is third/fourth lowest for the day, in contrast with extent. That still may change.
Area is still 3rd lowest, but closing in on 2012 and 2016 the last 2 days.

I attach the NSIDC Area daily change graph and the PIOMAS daily change graph for Jun 30 to 1 Aug.. Both show large losses in the first week of July and average to below average losses from the second week to the 15th/16th. They match pretty well, despite the area data being the 5 day trailing average.

In the last 2 days daily area loss has increased again just when the season on average is past its peak daily losses. A good chance PIOMAS daily losses will follow suit?
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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3361 on: July 19, 2020, 08:08:12 PM »
I attach 2 tables & a graph on PIOMAS volume as at mid-July (15th or 16th July).

The previous 10 years average remaining volume los would give a minimum of 3.88 '000 km3, second lowest behind 2012.

But the way this season has gone so far...........
« Last Edit: July 19, 2020, 08:16:05 PM by gerontocrat »
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jdallen

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3362 on: July 19, 2020, 08:28:28 PM »
I attach 2 tables & a graph on PIOMAS volume as at mid-July (15th or 16th July).

The previous 10 years average remaining volume los would give a minimum of 3.88 '000 km3, second lowest behind 2012.

But the way this season has gone so far...........
I think it's worth mentioning that the lions share of that 0.436 thousand km3 difference between 2020 and 2019 is subsumed by the Greenland and Chukchi seas.
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oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3363 on: July 20, 2020, 04:42:23 AM »
Time for the prediction of volume for the September minimum. Please zoom the regional charts above to follow the analysis.
Of the seas traditionally participating in the minimum, the Laptev is nearly zero now. The ESS is record low. The Kara is very low. The Barents is on the low side. Chukchi is rather low as well. All are assumed to be zero in September - for some of these seas that is a very common achievement, for some a rather rare one.

We remain with the four unknowns:
* Greenland Sea - has been running high since spring. I expect it to crash at some point due to melting and lack of imports, especially now that most of the thick ice at the export region has disappeared. My bet is somewhere above 2019 but far below 2012. 125 km3.
* CAA - had a very slow start, but a fast decline. Temps have been running very high for a month. I expect a result above 2012/2011 but probably below 2019. 100 km3.
* Beaufort - the most anomalous. Has been running high and getting higher, due to extra imports and lower exports. I can't see it heading towards near-zero, and foresee a high volume, probably somewhere below 2013's 200 km3, but above 2018's 80 km3. 125 km3.
* CAB - naturally the most variable in magnitude. has been running high in winter and spring, only to crash in the last month back into the fold. From where we are now it is quite common to reach 4000-4200 km3. Following the high losses of 2007, 2012, 2016, we might get to 3600 km3, still above 2012's minimum of 3400 km3. And who knows? We might break loss records, and perhaps even reach a CAB record in September.

Summing everything, we get 350 km3 outside the CAB. With a reasonable/aggressive scenario of 3600 km3 in the CAB, we get a total of 3950 km3, a respectable 2nd, lower than 2019's 4050 km3, but still much higher than 2012's 3670 km3.
However, my money is still on a record low volume. I am betting the impact of the GAAC was partially missed by the model, and will be incorporated later when ice area crashes. In addition, early open water on the Siberian side might eat deeper into the CAB than usual. If a CAB record can be achieved, total volume will probably also reach a record low.

Aluminium

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Re: Latest PIOMAS update (June 2020, mid-monthly update)
« Reply #3364 on: July 20, 2020, 10:14:29 AM »
Changes from June 30.

Laptev ... -89%
Hudson ... -85%
Barents ... -77%
Kara ... -73%
Baffin ... -71%
ESS ... -68%
Chukchi ... -46%
Greenland ... -26%
CAA ... -21%
CAB ... -19%
Beaufort ... -19%

Tor Bejnar

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3365 on: July 20, 2020, 02:16:59 PM »
Aluminium,
This presentation will be dramatic at the end of the melt season when the CAB starts growing while other areas continue to loose ice.  (I wonder what the rim colour will be!)
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Neven

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3366 on: July 20, 2020, 02:44:49 PM »
I noticed Wip updated this graph, showing JAXA thickness (unreliable, but still interesting):
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gerontocrat

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3367 on: July 20, 2020, 04:18:04 PM »
I noticed Wip updated this graph, showing JAXA thickness (unreliable, but still interesting):
I forgot these were in one of my spreadsheets, so I've dusted off the cobwebs and here they are.

Thickness graphs (PIOMAS volume / NSIDC Area)-
- Total Arctic,
- High Arctic Seas total
- Peripheral Arctic Seas total,
- Greenland Sea - will be the only peripheral sea left of any significant ice in it by end July.
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oren

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Re: Latest PIOMAS update (July 2019)
« Reply #3368 on: July 21, 2020, 04:58:09 AM »
Hi Wipneus, could you please provide an update of the gice charts? (Area and volume by thickness categories). It would be very interesting this year.

Another question Wipneus, you posted a chart last year that showed the distribution of PIOMAS thickness bins and was a good predictor of area at minimum, if I am not mistaken. Could you post it again this year?

That would be the gice graphs. For an explanation of gice see https://forum.arctic-sea-ice.net/index.php/topic,119.msg152005.html#msg152005

Attached are the 30th June graphs.

Wipneus

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Re: Latest PIOMAS update (July 2019)
« Reply #3369 on: July 21, 2020, 08:13:40 AM »
Hi Wipneus, could you please provide an update of the gice charts? (Area and volume by thickness categories).

The gice data has not been updated since mid 2019.

Quote
It would be very interesting this year.

Agreed, I will ask Dr. Zhang.

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3370 on: July 21, 2020, 08:31:10 AM »
Thank you Wipneus.

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3371 on: July 22, 2020, 04:49:23 AM »
Following a discussion from another thread, here is the promised chart of PIOMAS volume divided by UH area, a measure of average thickness.
Please note that due to the wide distribution of ice thicknesses, and by the definition of the measure, average thickness will often rise (or slow down its drop) in times of accelerated area loss, and will drop sharply during initial ice regrowth.
Click each chart to enlarge and zoom.

Notes: Thanks to Wipneus for both sets of data. Some missing UH values were interpolated manually.

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3372 on: July 22, 2020, 08:00:49 AM »
Following a discussion from another thread, here is the promised chart of PIOMAS volume divided by UH area, a measure of average thickness.
Please note that due to the wide distribution of ice thicknesses, and by the definition of the measure, average thickness will often rise (or slow down its drop) in times of accelerated area loss, and will drop sharply during initial ice regrowth.
Click each chart to enlarge and zoom.

Notes: Thanks to Wipneus for both sets of data. Some missing UH values were interpolated manually.

Hmm, I thought the PIOMAS raw output was a thickness map, and this had to be masked with an area map to produce a volume figure. And this mask is normally NSIDC area, so I wanted to see what the volume would be if the thickness was masked with the AMSR2 area instead, that's what I meant in the other thread.
In your charts however, it goes the other way: The PIOMAS volume from Wipneus is used as is, and divided by the AMSR2 area, to give a different thickness than PIOMAS originally produced. But this means that the PIOMAS volume input for your equation is already masked with the NSIDC area, no? Or am I misunderstanding something?

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3373 on: July 22, 2020, 11:03:53 AM »
PIOMAS output is many files of which I know nothing about. Wipneus processes them and provides downloadable aggregate data (divided by regions) on his website, as well as the animations and charts posted here every two weeks. I lack the ability to do geographical/gridded processing of PIOMAS output.
I took the total volume provided by Wipneus and divided by the total UH area, also provided by Wipneus... I occasionally do the same for sub-regions, specifically the CAB. Obviously the average thickness provided by PIOMAS directly would be of better value than this rather crude approximation.

PIOMAS is masked with NSIDC extent (as much as I understand the question, and the issue) but assimilates NSIDC ice concentration ("area") as part of its inputs.
In any case it would be wrong to mask the PIOMAS map or output files with the AMSR2 area map. If I understand correctly, the main goal of PIOMAS is to model the volume, rather than its very specific location. So cutting off parts of the map using a mask that did not serve as input to PIOMAS would not be calculating a valid value.

Wipneus

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3374 on: July 22, 2020, 01:49:34 PM »
Thanks to DR. Zhang we have updated gice files as well. Gice gives information about the thickness variations in each of the cells in the PIOMAS grid. I have tried to explain the details  of gice here: 
https://forum.arctic-sea-ice.net/index.php/topic,119.msg152005.html#msg152005

From gice I can calculate the area occupied from ice with thickness in each of the 12 thickness categories.
The attached graph shows this for each of the years in the PIOMAS data set. The area of all categories with thickness larger than zero is the PIOMAS area figure. PIOMAS area near the minimum, I take 10th of September, is plotted as a dashed line.

The naive explanation is that before 2007 about 26 cm of ice would be melted by the end of the melting season. The final area more or less follows the >26cm category. After 2007 that figure is about 71cm, after 2007 final area follows the >71cm cat, with variations less than half a million km2.

Ice of 71 cm and higher has the lowest area on day 197 of all years. To beat 2012 September area it has to go quite a bit lower than that, as 2020 managed to melt quite some ice in the >71cm category.

Wipneus

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3375 on: July 22, 2020, 01:55:38 PM »
You can of course also plot ice volume per category.

Tom

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3376 on: July 22, 2020, 02:20:38 PM »
That first graph seems to show that we should expect extent/area loss to continue.

I say this because the area taken by ice <0.26m ice is larger than previous years.

oren

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3377 on: July 22, 2020, 06:46:53 PM »
Thank you Wipneus.
I note 2020 is the lowest for the date on both the >71cm ice and on the >26cm ice. I also note that the reason 2020 has slightly higher volume than 2019 and 2012 is the volume contained in the very thick ice, >4.23m. My conclusion is that at least according to PIOMAS this year does not have good defenses against a a new record area/extent - there isn't more volume where it counts. OTOH, unless that super-thick ice happens to be exported, it means this year has a bit of buffer to overcome before it can break the record low volume.

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3378 on: July 22, 2020, 08:06:08 PM »
<snippage> My conclusion is that at least according to PIOMAS this year does not have good defenses against a a new record area/extent - there isn't more volume where it counts. OTOH, unless that super-thick ice happens to be exported, it means this year has a bit of buffer to overcome before it can break the record low volume.
I'm pessimistic about that buffer, in part because there is little to protect it.  I'm keeping in mind this was the estimate from a week ago, and the melt since then has been significant and much higher than average.

I'm reasonably confident pretty much anything <= 71cm will melt out, and a lot of ice that is thicker will also, due to the fact it is no longer contiguous, and will be exposed once the thinner ice is removed.  That's one of the "intangible" problems we have, regarding the quality of the pack.  Distribution counts, and outside of a relatively small region (< 2 million km2) backed up to the CAA ice quality is awful.
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Lord M Vader

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Re: Latest PIOMAS update (July 2020, mid-monthly update)
« Reply #3379 on: August 03, 2020, 08:57:16 AM »
August 3 today. Let's see if the volume numbers for July will show up today. And if we will get a new record low volume for July 31.

Wipneus

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Re: Latest PIOMAS update (August 2020)
« Reply #3380 on: August 04, 2020, 09:56:26 AM »
PIOMAS gridded thickness data is updated to day 213 (31Jul/1Aug). The (calculated) volume on that day was 6.52 [1000km3], second lowest (behind 2019).

Here is the animation.

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Re: Latest PIOMAS update (August 2020)
« Reply #3381 on: August 04, 2020, 10:05:52 AM »
The volume and volume-anomaly graphs.

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Re: Latest PIOMAS update (August 2020)
« Reply #3382 on: August 04, 2020, 10:08:20 AM »
Fram volume export graph.

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Re: Latest PIOMAS update (August 2020)
« Reply #3383 on: August 04, 2020, 10:23:39 AM »
Thickness map compared with previous year and their differences.

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Re: Latest PIOMAS update (August 2020)
« Reply #3384 on: August 04, 2020, 10:26:04 AM »
Some people have use for the updated regional data files:

monthly:
https://sites.google.com/site/arctischepinguin/home/piomas/data/PIOMAS-regional-monthly.txt.gz
daily:
https://sites.google.com/site/arctischepinguin/home/piomas/data/PIOMAS-regional.txt.gz

In case anyone wonders, there is no daily gice update yet.

BornFromTheVoid

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Re: Latest PIOMAS update (August 2020)
« Reply #3385 on: August 04, 2020, 11:27:40 AM »
A focus on July and the larger picture.

Gap to lowest on record down to just 150 km3
I recently joined the twitter thing, where I post more analysis, pics and animations: @Icy_Samuel

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Re: Latest PIOMAS update (August 2020)
« Reply #3386 on: August 04, 2020, 12:03:38 PM »
So average loss from day 182 till 213 in 2010-2019 = 5.762; 2020 is 6.016
As percentage average loss is 43,9% and 2020 = 48,0%

Gap with nr. 1 position was 745 on day 182
Gap with nr. 1 position is 145 on day 213

This has been an extraordinary july based on PIOMAS data

Average (last 10 years) august losses will bring us at 4.625 on day 234, that will be 3rd position (2019: 4.561; 2012: 4.297)

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Re: Latest PIOMAS update (August 2020)
« Reply #3387 on: August 04, 2020, 12:27:13 PM »
OK so if I understood correctly the volume of the ice has decreased by 5,587 km3 in July 2019 and by 6,010 km3 in 2020.

12,050-6,463 = 5,587 km3 in 2019.
12,530-6,520= 6,010 km3 in 2020

The trend for the end of August does not look very good to me.
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oren

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Re: Latest PIOMAS update (August 2020)
« Reply #3388 on: August 04, 2020, 01:57:59 PM »
First of all big thanks to Wipneus as usual for providing PIOMAS data in a digestible format.
Looking at the most recent update, it continues the trends of the summer:
* CAB volume loss for the period shattered the record again (long held by 2007 for 2H July), losing 205 km3 more than 2012 and 262 km3 over 2019, but is still not at record low. Almost.
* Beaufort still high.
* Siberian seas still at record low.
* CAA and Chukchi still on the low side.
* Greenland Sea still on the high side.
* 2012 still has the upcoming August advantage and will need some effort to catch up.
* I still predict a record low volume due to the high energy received in July, and the way the ice looks on Worldview and AMSR. And I still can't justify it with the numbers, who are pointing to 2nd-3rd finish.

I will post some reginal charts and numbers later.
« Last Edit: August 04, 2020, 03:40:20 PM by oren »

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Re: Latest PIOMAS update (August 2020)
« Reply #3389 on: August 04, 2020, 02:30:00 PM »
First of all big thanks to Wipneus as usual for providing PIOMAS data in a digestible format.
Looking at the most recent update, it continues the trends of the summer:
* CAB volume loss for the period shattered the record again (long held by 2007 for 2H July), losing 205 km3 more than 2012 and 262 km3 over 2019, but is still not at record low. Almost.
* Beaufort still high.
* Siberian seas still at record low.
* CAA and Chukchi still on the low side.
* Greenland Sea still on the high side.
* 2012 still has the upcoming August advantage and will need some effort to catch up.
* I still predict a record low volume due to the high energy received in July, and the way the ice looks on Worldview and AMSR. And I still can't justify it with the numbers, who are pointing to 2nd-3rd finish.

I will post some reginal charts and numbers later.

Hello Oren, first of all I would like to thank you for everything you are willing to share with us. You are doing a remarkable job just like Gerontocrat, Wipneus, Juan C. Garcia etc... (too numerous to mention them all here).
Could you explain to me how you arrive at a loss of volume for the year 2020 of 262 km3 greater than that of 2019? While I calculated (with the numbers provided by Wipneus here on this thread) a loss of 423 km3 more than in 2019. See my previous post.
6010-5587= 423
Where did I go wrong?
Thank you
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oren

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Re: Latest PIOMAS update (August 2020)
« Reply #3390 on: August 04, 2020, 03:42:24 PM »
I meant just the loss of volume in the region of the CAB. This is considered the hardest ice to melt, so I often focus on it in my analysis. Your numbers are for the total volume loss for all regions.

Edit: in addition, my numbers were for only the 2nd half of July, while yours were for the whole month.
« Last Edit: August 04, 2020, 04:34:31 PM by oren »

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Re: Latest PIOMAS update (August 2020)
« Reply #3391 on: August 04, 2020, 05:13:22 PM »
I meant just the loss of volume in the region of the CAB. This is considered the hardest ice to melt, so I often focus on it in my analysis. Your numbers are for the total volume loss for all regions.

Edit: in addition, my numbers were for only the 2nd half of July, while yours were for the whole month.

Yes, of course, I'm sorry for the mix-up. As I don't speak English very well I use an automatic translator, which is not very good and my attention is sometimes diverted from the essential. And I'm not talking about the misunderstandings... I'll try to be more attentive. :-[
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Re: Latest PIOMAS update (June 2020, mid-monthly update)
« Reply #3392 on: August 04, 2020, 11:19:53 PM »
Changes from July 15.

Laptev ... -94%
Barents ... -91%
Hudson ... -90%
Kara ... -84%
ESS ... -80%
Baffin ... -68%
Chukchi ... -61%
CAA ... -45%
Beaufort ... -35%
Greenland ... -32%
CAB ... -21%

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Re: Latest PIOMAS update (August 2020)
« Reply #3393 on: August 05, 2020, 12:08:16 PM »
A focus on July and the larger picture.

Gap to lowest on record down to just 150 km3


Hello BornFromTheVoid, I am pleased to see you again regularly on ASIF. I seem to recall that you left us to pursue graduate studies.
You say there's a 150-km3 differential between 2019 and 2020, right? It seems to me that the differential is only 57 km3 between the two.
6.520-6.463=57
Where did I go wrong?
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Re: Latest PIOMAS update (August 2020)
« Reply #3394 on: August 05, 2020, 12:13:48 PM »
I think your 6.463 is not correct

Value 2020 on day 213 = 6.516
Value 2019 on day 213 = 6.371

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Re: Latest PIOMAS update (August 2019)
« Reply #3395 on: August 05, 2020, 12:26:32 PM »
PIOMAS gridded thickness data was updated. I calculate volume from the thickness data, gives 6.46 [1000km3] on 2019-07-31. Lowest for the day with a small margin with 2012 (6.68 [1000km3]).

Here is the animation.
I think your 6.463 is not correct

Value 2020 on day 213 = 6.516
Value 2019 on day 213 = 6.371

Hello RikW, Here is the origin of the numbers I am reporting. I can't figure out where the error came from. Did Wipneus make a correction? Did I get the dates and numbers wrong? But where then?
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Re: Latest PIOMAS update (August 2020)
« Reply #3396 on: August 05, 2020, 12:35:26 PM »
I've got a slightly different number in the PIOMAS data, so maybe PIOMAS recalculated it, and a day difference, probably because of the leap year?

Don't know if it's better to stick to calender date or to date number; I think with PIOMAS the latter is better, because they don't have december 31st data in leap years...

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Re: Latest PIOMAS update (August 2020)
« Reply #3397 on: August 05, 2020, 12:56:11 PM »
I've got a slightly different number in the PIOMAS data, so maybe PIOMAS recalculated it, and a day difference, probably because of the leap year?

Don't know if it's better to stick to calender date or to date number; I think with PIOMAS the latter is better, because they don't have december 31st data in leap years...

Indeed, day 213 in 2019 corresponds to August 1, 2019 and not July 31, 2019. But that would mean that PIOMAS gives figures from day to day, it seems strange to me, I thought the calculations were only done twice a month with the posts of Wipneus  ;).
Thank you for your help
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Re: Latest PIOMAS update (August 2020)
« Reply #3398 on: August 05, 2020, 04:58:56 PM »
PIOMAS calculate twice a month but in any case they keep dates by day numbers. To compare you must take day 213, not same date, from both years.

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Re: Latest PIOMAS update (August 2020)
« Reply #3399 on: August 06, 2020, 06:01:55 AM »
Some PIOMAS charts and data, as promised.
Total volume is headed straight towards a 1st-3rd rank finish, strong achievement from a year that had a nice and cold winter and a relatively high max volume. The daily records diagram contrasts with 2017 and other years that had an early lead but petered out along the way.
The CAB is the biggest story this year. The amount of sunshine received in July with clear skies and very low albedo is very apparent in PIOMAS volume (though personally I doubt the model captures the whole phenomenon). A table of losses for each of the last three periods shows how rare was the CAB melting performance. Previous summer volume losses tended to cluster, but this year blew the numbers out of the water.

Poor Phoenix noticed the clustering and was quite certain this year had no chance at any records. Well life has its way with surprises, rereading the prediction made two months ago is almost funny, even though he wasn't wrong with identifying past behavior. Bolding mine.
As I look at the information and try to explore what it means for projecting the minimum, I am drawn to a feature of the CAB chart where the vast majority of the ice is  going to be at the minimum.

The chart indicates very little annual variation in CAB volume loss from days 165 to 210 with an exception for 2017 in days 165 to 180. (Edit: 2014 is also an exception with low CAB loss during peak season). This period of low variation coincides with a period of low temperature variation as shown in 60+ years of DMI 80N temperatures.

It suggests that the primary opportunity for a year to differentiate itself in CAB volume loss performance is limited and needs to come before or after this 45 day window. With the early season window approaching a close and limited current momentum, it seems the possibilities for 2020 to break new ground is dependent on performance after Aug 1.