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Author Topic: Latest PIOMAS update (June - mid month update)  (Read 499406 times)


FishOutofWater

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Re: Latest PIOMAS update (April)
« Reply #1601 on: April 14, 2017, 06:03:45 PM »
Repeated strong high latitude atmospheric blocking, combined with persistent low pressure over the Arctic ocean drove warm air from the Pacific and Atlantic oceans, repeatedly over the Arctic. This lead to record warmth over the Arctic ocean and inhibited sea ice growth. Moreover, the pattern favors increased warm Atlantic water inflow through the Fram strait.

Thus PIOMAS now shows record low sea ice volume for March.

PIOMAS is the best physical model we have, but it does not predict the weather. No curve fitting has the physics of PIOMAS. The arguments over curve fitting are meaningless.

This winter's weather was unprecedented. We're in uncharted waters. It's going to take atmospheric scientists several years, at least, to understand what's happening with the unprecedented weather.

Research to date indicates that there may be a feed back between the low sea ice volume and the weather. Thus we're dealing with a possible tipping point, because the system is potentially unstable.

Which brings up back to watching the PIOMAS thickness results. The science to predict accurately what the sea ice will look like two or three summers from now does not yet exist. The best we can do is to make accurate observations. Predictions are not reliable.

prokaryotes

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Re: Latest PIOMAS update (April)
« Reply #1602 on: April 14, 2017, 06:20:40 PM »
And then there is the Arctic air intrusion into lower latitudes, ie. The highs of 25 ºC last week will seem like a distant memory as it turns colder this #EasterWeekend, as cooler air comes down from the north https://twitter.com/metoffice/status/852902667064102912 Like to read a bit more updates on the historical perspective on this, and frequency and such, and in relation to the Polar Vortex pressure.

Rick Aster

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Re: Latest PIOMAS update (April)
« Reply #1603 on: April 14, 2017, 06:56:33 PM »
And then there is the Arctic air intrusion into lower latitudes
...
Like to read a bit more updates on the historical perspective on this, and frequency and such, and in relation to the Polar Vortex pressure.


You won't find much of that in the Cryosphere part of the forum, which is mostly about the higher latitudes, but try the Consequences part, particularly "Topic: Weird Weather and anecdotal stories about climate change" http://forum.arctic-sea-ice.net/index.php/topic,323.0.html

prokaryotes

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Re: Latest PIOMAS update (April)
« Reply #1604 on: April 14, 2017, 07:02:25 PM »
You won't find much of that in the Cryosphere part of the forum...

Thanks, was just mentioning it because of what appears to be FOOW's excellent blog -
 and thought it was worth mentioning because of the interconnections http://www.dailykos.com/blog/FishOutofWater

oren

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Re: Latest PIOMAS update (April)
« Reply #1605 on: April 14, 2017, 07:33:47 PM »
Just a quick one. 2017 has build a big lead over 2012 in the race for the lowest annual minimum (Arctic Sea Ice) volume.

The graph shows that most of the lead was gained in the freezing season: end-October/begin-November, followed by a smaller spurt in December. The bump in February, followed by the slow decrease in March may or may not be regarded as "noise". No regression toward the mean indeed.
I too think this chart is very disturbing. The low autumn volume should have caused the ice to thicken more later, but it didn't. And the continued strong export of old ice into the Atlantic gives good cause to believe that end-April PIOMAS numbers will be as bad.
My only (slim) hope at this stage is that PIOMAS somehow made a mistake in concentrating all the volume in that moving "blob" further to the north of Greenland, while past years, and other models such as Hycom, put it closer to Greenland in the protected Lincoln Sea. In which case more volume might actually emerge out of the winter than the number claimed by PIOMAS.
btw the FDD anomaly shows a similar trend, most of it happened in the autumn and only a little was added over the winter - but there was no mean reversion.

AndrewB

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Re: Latest PIOMAS update (April)
« Reply #1606 on: April 14, 2017, 08:07:55 PM »
...
Thus PIOMAS now shows record low sea ice volume for March.
...

Actually just look at the chart posted by prokaryotes in the comment just before yours, and you'll notice that PIOMAS has been showing record low Arctic sea ice volume for the months of December 2016, and January, February and March 2017.

: FishOutofWater
...
Predictions are not reliable.

Here is one prediction that I am reasonably confident about: PIOMAS for April 2017 will also be a record monthly low.  ;)

prokaryotes

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Re: Latest PIOMAS update (April)
« Reply #1607 on: April 14, 2017, 08:31:20 PM »
Will there be impact on the Greenland surface melt, like we had in 2012? So far not much? (tick 2017 to compare 2012 with 2017 in NSIDC interactive graph)
http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart

Notice NSIDC stated April 3, 2017
Daily updates have resumed for the 2017 melt season. Bit puzzling, according to the data not a single melt day so far?

In recent decades, the Greenland ice sheet has experienced increased surface melt. However, the underlying cause of this increased surface melting and how it relates to cryospheric changes across the Arctic remain unclear. Here it is shown that an important contributing factor is the decreasing Arctic sea ice. Reduced summer sea ice favors stronger and more frequent occurrences of blocking-high pressure events over Greenland. Blocking highs enhance the transport of warm, moist air over Greenland, which increases downwelling infrared radiation, contributes to increased extreme heat events, and accounts for the majority of the observed warming trends. These findings are supported by analyses of observations and reanalysis data, as well as by independent atmospheric model simulations using a state-of-the-art atmospheric model that is forced by varying only the sea ice conditions. Reduced sea ice conditions in the model favor more extensive Greenland surface melting. The authors find a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance. This linkage may improve the projections of changes in the global sea level and thermohaline circulation.
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0391.1
« Last Edit: April 14, 2017, 08:37:35 PM by prokaryotes »

Neven

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Re: Latest PIOMAS update (April)
« Reply #1608 on: April 14, 2017, 10:58:36 PM »
From now on I only want to see comments on PIOMAS now/near real-time and nothing about Greenland or other tangential stuff. I have put on my snipping gloves.
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Tigertown

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Re: Latest PIOMAS update (April)
« Reply #1609 on: April 14, 2017, 11:13:04 PM »
The Open Thread is getting lonely. Why not use it.

https://forum.arctic-sea-ice.net/index.php/topic,1884.250.html#lastPost

Shared Humanity

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Re: Latest PIOMAS update (April)
« Reply #1610 on: April 14, 2017, 11:44:27 PM »
As of April 13, Sea Ice Extent, at 13,155,325 km2, is in a dead heat with 2016. Meanwhile PIOMASS shows that volume is 2000 cubic km below 2016. We have a whole lot of thin ice out there. If we want to understand how this melt season will play out, we need to look at where the CAB will go 'early ice free' and how early this will happen. I am particularly concerned with those areas that are dominated with ice below 2 meters thick. There are large areas where ice is no more than 1.5 meters thick.

Obviously, the FDD anomaly did a whole lot of damage to ice in the CAB and warm winters are becoming the new normal.

Would not be surprised if we see record lows in all three metrics at the end of this melt season.
« Last Edit: April 14, 2017, 11:51:10 PM by Shared Humanity »

rboyd

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Re: Latest PIOMAS update (April)
« Reply #1611 on: April 15, 2017, 12:57:49 AM »
<snip, wrong place: N.>
« Last Edit: April 15, 2017, 10:28:04 AM by Neven »

Jim Williams

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Re: Latest PIOMAS update (April)
« Reply #1612 on: April 15, 2017, 01:10:25 AM »
<snip, wrong place: N.>

<snip, wrong place: N.>

« Last Edit: April 15, 2017, 10:28:29 AM by Neven »

Wipneus

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Re: Latest PIOMAS update (April)
« Reply #1613 on: April 15, 2017, 03:05:56 PM »
Andreas T asked me the following question:

: Andreas T date=1492254011
I am using AMSR layers on worldview to get estimates of area export through Fram. To make sure what I do is comparable to your PIOMAS volume exports, can you tell me (posting on the forum perhaps) what the reference points for theses values are? I.e. boundary, and time intervals (end of month or mid month)
Thank you for all the work you are doing on this
Andreas

Hi Andreas,

Attached is a map with the PIOMAS grid on it.

I choose the pink pixels because they are aligned on a meridian in the PIOMAS grid and bridge the Strait in the least number of grid cells (there are a few more). Not that it matters a lot, calculating transport at another "crossing" makes little difference.

PIOMAS data gives me:
- average ice thickness in each cell
- velocity in the direction of the crossing
- cell dimensions, in this case the cell width (in the direction of the crossing)

the volume transport per cell is given by:

  thickness*velocity*cell-width

Summing the cells shown in the map, gives total volume export

I can do this monthly thickness and velocity data. Daily data is possible as well but the noise is incredible, filtering gives results similar to using monthly data.

 




Shared Humanity

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Re: Latest PIOMAS update (April)
« Reply #1614 on: April 15, 2017, 04:01:41 PM »
You are a Wizard!

Andreas T

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Re: Latest PIOMAS update (April)
« Reply #1615 on: April 15, 2017, 08:08:54 PM »
thank you Wipneus, nice to see a little "under the bonnet" of the PIOMAS model

The purpose of my effort here is to get a comparison via a different approach of the current rate of export with other years (although this is too cumbersome to do for a lot more months)
While AMSR2 data is only available since 2016, there are AMSRE data shown on worldview and I picked 2009 as an example of high export in the PIOMAS output.

I am attaching an animation of Feb / Mar / Apr 2009 with ice area which crossed 80N before 1. May marked by red dots and orange lines at end of month
a bit of work in progress but I want to see if this works before I continue
position of the dots on 2. Feb 2009:
 84,9N / 28.2W
 85.7N / 2.9W
 85.2N/ 22.8E
 eastern edge 25E
« Last Edit: April 16, 2017, 12:19:54 PM by Andreas T »

Andreas T

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Re: Latest PIOMAS update (April)
« Reply #1616 on: April 15, 2017, 08:13:42 PM »
gif does not seem to play, any suggestions?

Hyperion

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Re: Latest PIOMAS update (April)
« Reply #1617 on: April 16, 2017, 01:21:07 AM »
Hmmm. With the kill zone extending all the way to FJL, and Bering and Nares etc also being very active, I wonder if the real toll might be closer to 3x what Frams been gobbling.
the other concern I have is how much of the surface water is being exported and lost with that Ice. the Ice may only average ¬2m, but is 10m or even 20m of low salinity water going along  with it?  ???
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Wipneus

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Re: Latest PIOMAS update (April)
« Reply #1618 on: April 16, 2017, 08:46:52 AM »
gif does not seem to play, any suggestions?

Forum software is picky/buggy. Change something to the file, eg shave of some pixels and it may work.

Andreas T

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Re: Latest PIOMAS update (April)
« Reply #1619 on: April 16, 2017, 12:47:56 PM »
Thanks, made some small changes, working now.
@Hyperion, no the other outlets to the Atlantic / Barents Sea definitely carry much less export.
have a look at https://www.climate.gov/news-features/videos/old-ice-arctic-vanishingly-rare
or see http://ocean.dmi.dk/arctic/icedrift/index.uk.php for more recent movement

gerontocrat

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Re: Latest PIOMAS update (April)
« Reply #1620 on: April 25, 2017, 03:25:11 PM »
Being addicted to volume data, while waiting for the PIOMAS monthly update I go to ArctischePinguin to pick up the Jaxa-amsr2-volume graph. It shows a 2000 km3 increase in volume at the beginning of April which as yet persists.

This is in complete contrast to the numerous physical observations, images and animations posted all over the ASIF Arctic sea ice threads indicating the disastrous state of the ice-cap . I am confused (situation normal).


Shared Humanity

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Re: Latest PIOMAS update (April)
« Reply #1621 on: April 25, 2017, 03:29:04 PM »
Being addicted to volume data, while waiting for the PIOMAS monthly update I go to ArctischePinguin to pick up the Jaxa-amsr2-volume graph. It shows a 2000 km3 increase in volume at the beginning of April which as yet persists.

This is in complete contrast to the numerous physical observations, images and animations posted all over the ASIF Arctic sea ice threads indicating the disastrous state of the ice-cap . I am confused (situation normal).

Have gone through life confused much of the time.

Juan C. García

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Re: Latest PIOMAS update (April)
« Reply #1622 on: April 25, 2017, 03:59:31 PM »
Being addicted to volume data, while waiting for the PIOMAS monthly update I go to ArctischePinguin to pick up the Jaxa-amsr2-volume graph. It shows a 2000 km3 increase in volume at the beginning of April which as yet persists.

This is in complete contrast to the numerous physical observations, images and animations posted all over the ASIF Arctic sea ice threads indicating the disastrous state of the ice-cap . I am confused (situation normal).

Have gone through life confused much of the time.

It is normal to have the maximum extent in March. However, it is also normal that the ice thickness increases until April. For that reason, it is normal that the maximum in volume happens in April.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

jai mitchell

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Re: Latest PIOMAS update (April)
« Reply #1623 on: April 25, 2017, 04:03:11 PM »
There is also some possibility that the abnormally low thickness average could produce conditions for later season growth at peak.
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crandles

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Re: Latest PIOMAS update (April)
« Reply #1624 on: April 25, 2017, 04:06:40 PM »

It is normal to have the maximum extent in March. However, it is also normal that the ice thickness increases until April. For that reason, it is normal that the maximum in volume happens in April.


PIOMAS has extent maximum in March, volume maximum mid April and average thickness maximum late April / early May.



ie after max volume, extent is going down faster than volume so that volume/extent continues to increase for a short while.

Juan C. García

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Re: Latest PIOMAS update (April)
« Reply #1625 on: April 25, 2017, 04:15:58 PM »
Piomas volume monthly data (1000 km3), with minimums highlighted. I will expect that 2017 will have new minimum records on April and May, at least. That will make seven consecutive records (from November 2016 to May 2017). Afterwards, the minimum was stablish on 2012. So 2017 will be in direct competence with 2012 minimum, from June to October.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

oren

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Re: Latest PIOMAS update (April)
« Reply #1626 on: April 25, 2017, 05:24:46 PM »
Thank you Juan for this excellent table. I love it.
Eyeballing the numbers for the hundredth time, I would hazard the following guesses regarding upper volume limits, based on past performance and unreliable gut feeling:
April 20.800
May 19.800
June 15.800 (still a record though barely)
In terms of probability I wouldn't be surprised to see lower numbers, even much lower, but I would be surprised to see higher numbers.

crandles

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Re: Latest PIOMAS update (April)
« Reply #1627 on: April 25, 2017, 07:16:30 PM »
I get different numbers

:
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg
2007 18.377 20.863 23.031 23.764 23.078 19.11 12.038 7.582 6.528 7.135 10.472 14.238 15.480
2008 18.58 21.579 23.863 24.995 24.102 20.498 14.061 9.154 7.246 8.309 11.759 15.197 16.576
2009 18.852 21.729 23.827 24.957 23.851 19.649 12.733 8.235 6.923 7.664 10.813 14.242 16.083
2010 17.723 20.631 23.121 24.103 22.181 17.044 10.153 5.888 4.748 6.237 9.535 12.984 14.486
2011 16.261 19.37 21.421 22.51 21.108 16.403 9.457 5.453 4.484 5.754 9.316 13.052 13.675
2012 16.945 19.63 21.964 23.13 21.677 15.896 9.177 4.923 3.789 5.036 8.276 12.195 13.512
2013 15.862 19.376 22.001 23.131 21.839 17.447 10.446 6.361 5.483 6.996 10.13 13.85 14.373
2014 17.46 19.887 21.838 22.946 21.878 17.6 11.88 8.114 6.975 8.201 11.541 15.13 15.255
2015 18.502 21.508 23.244 24.239 23 18.467 11.55 7.047 5.854 7.052 10.354 14.061 15.364
2016 17.234 19.633 21.559 22.472 20.993 16.408 10.169 5.897 4.533 5.537 7.882 11.266 13.591
2017 14.695 17.414 19.632
Projection w max 20.798 20.112 16.508 10.788 7.022 6.144 7.657 11.219 15.138 12.566
Projection w min 20.365 18.443 12.662 5.59 0.683 -1.225 -0.618 1.727 5.111 9.488

We seem likely to get a record low average for year even following max changes from one month to the next from last 10 years.

oren

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Re: Latest PIOMAS update (April)
« Reply #1628 on: April 25, 2017, 08:45:25 PM »
In guessing I relied on the peculiar fact that in all past years in the table May volume did not exceed March volume by more than 150250, regardless of April variability.
« Last Edit: April 26, 2017, 12:36:22 AM by oren »

Juan C. García

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Re: Latest PIOMAS update (April)
« Reply #1629 on: April 25, 2017, 11:45:18 PM »
Thank you Crandles and Oren for your comments. I didn't notice before that the thickness grows until early May.
Regarding the values that I used on Piomas Monthly Volume, I took it directly from Piomas, so they are the official monthly data.
I made a forecast, looking to the max and min change between a given month and March, for each year, on 2007-2016.
So the maximum value for September is if 2017 follows the path of 2014, which will bring a value of 4.77k km3.
The minimum value for September is if 2017 follows the path of 2010, which will bring a value of only 1.26k km3.
The average of both values is 3.01k km3, that will be a huge record, if it happens.  :o
In both cases, max and min, the average of the year will be less than the average of 2012: 13.55k km3 (2012) versus 13.12k km3 (max) and 11.06k km3 (min).
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

crandles

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Re: Latest PIOMAS update (April)
« Reply #1630 on: April 25, 2017, 11:57:39 PM »
Regarding the values that I used on Piomas Monthly Volume, I took it directly from Piomas, so they are the official monthly data.

I averaged the daily volume numbers (well I trusted most of the numbers from https://sites.google.com/site/arctischepinguin/home/piomas ). The differences look to be too much for rounding down to 3dp and my numbers are higher by more than .03 or slightly more than .001 per day. Not sure why there would be that difference. Slightly odd but not important as the systematic error will be far greater than that.

Juan C. García

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Re: Latest PIOMAS update (April)
« Reply #1631 on: April 26, 2017, 12:57:46 AM »
Regarding the values that I used on Piomas Monthly Volume, I took it directly from Piomas, so they are the official monthly data.


I averaged the daily volume numbers (well I trusted most of the numbers from https://sites.google.com/site/arctischepinguin/home/piomas ). The differences look to be too much for rounding down to 3dp and my numbers are higher by more than .03 or slightly more than .001 per day. Not sure why there would be that difference. Slightly odd but not important as the systematic error will be far greater than that.


I took the Monthly data directly from Piomas. First you have to register on the second download (PIOMAS Monthly Ice Volume Data, 1979-present). Even that it says it is optional, it doesn't send the link unless you write your aswers:

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/data/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

gerontocrat

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Re: Latest PIOMAS update (April)
« Reply #1632 on: April 26, 2017, 04:10:55 PM »
Looking at the Jaxa AMSR2 volume graph from pinguin again, and at the relatively slow rate of melt so far this April, I am going to stick my neck out and say the PIOMAS analysis for April WILL be a minimum in the record, but the gap will be substantially reduced compared with that of the last few months.

I hope in about a fortnight I will be able to do a Winston Churchill and say "some chicken, some neck". (this was Churchill's riposte to a comment by Joseph Kennedy , USA Ambassador to the UK in 1940, on the likelihood of the UK surviving an invasion by Hitler's Third Reich).

The effect on the rest of the melting season - after 2012, who knows.

dj

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Re: Latest PIOMAS update (April)
« Reply #1633 on: April 27, 2017, 07:40:42 AM »
Rob, I hope I got the right place.  here is everything in somewhat chronological order.  Hope I got the overall gist of what was wanted . . .

Repost of what was original posted in "melting season".

Question:  I have used the PIOMAS volume and NSIDC area monthly averages to calculate thickness.  Has anyone noted the shift in timing of when maximal Arcic ice thickness occurs?  Or is this in some way an artifact that results from development of melt ponds early in the season?
I ask because there appears to be a dramatic shift from Sept/August to May/June.
I attribute this to a shift in the ratio of FYI to MYI with the first year ice rapidly melting off earlier.

First figure: Arctic Ice Thickness (m) reported as a stock with open, close, high, low.  Black = loss, White = Gain.
Second figure: Month of maximal thickness of Arctic Ice (from Sept to Aug).

(the figures are attached below again as I could not quote them)


I should point out, as confusing as it is - that for the second graph I used a single calendar year (Sept - Aug) instead of what is shown in the first graph (Sept to Sept), as I wanted to see if and when a shift occurred.
The first graph I made so that the students I teach could better "connect the dots" in that the start of one freeze/melt season was the finish of the prior freeze/melt season.

If that seems confusing - apologies.


Monthly figures are not good averages of the whole month often equate to value around 21/22nd of month. Better to do it with daily values. Using NSIDC extent I get

Max thickness Year day no. PIOMAS volume
2.318364396   1988 154  28.859
2.289274106   1989 138  29.582
2.288970221   1990 264  13.759
2.261284793   1991 162  27.703
2.25912203   1992 157  28.047
2.261604054   1993 152  28.114
2.254532152   1994 160  27.733
2.160511824   1995 145  26.678
2.118136706   1996 152  26.464
2.257689178   1997 152  27.747
2.197949979   1998 159  26.804
2.151437466   1999 174  23.498
2.09246973   2000 157  25.231
2.105114887   2001 167  23.912
2.110257681   2002 154  25.551
2.044730392   2003 131  26.696
2.045465942   2004 152  24.474
2.006957997   2005 154  23.652
1.95871678   2006 155  22.774
1.826859136   2007 146  22.527
1.894886364   2008 140  24.012
1.842512479   2009 153  22.147
1.743161214   2010 138  22.112
1.686625805   2011 134  21.464
1.695425125   2012 121  23.051
1.694907372   2013 138  21.866
1.753696131   2014 133  22.300
1.859662816   2015 128  23.826
1.795368353   2016 128  22.250

One year 1990 seems to have day of max pushed into Sept day 264. There is a local peak at day 155. Apart from this strange 1990 year that latest day is 174 23rd June.

Yes there is a noticeable trend towards earlier dates but it looks to me to be more like day 160 back to day 130.  Approx 30 days over 28 year period. That seems more in accordance with:



I started in 1988 due to every other day gaps prior to this in NSIDC extent.

Using area will probably make the September peak more prominent and hence your different results but it looks to be confusing 2 different peaks in the pattern like 1990 is messed up using extent.


Question:  I have used the PIOMAS volume and NSIDC area monthly averages to calculate thickness. 


Not advisable. Since NSIDC area monthly averages do not include the area of the pole hole, the values vary with the satellite of the date.

If you want to use area (and not extent), either use CT-area (stopped updating last year) or my daily values:
https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/data/nsidc_arc_nt_main.txt

Both make an assumption of the sea ice concentration within the pole hole from the measurements around it.
« Last Edit: April 27, 2017, 07:51:24 AM by dj »

Rob Dekker

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Re: Latest PIOMAS update (April)
« Reply #1634 on: April 27, 2017, 08:47:34 AM »
Thanks, dj.
It is clear from your post that the peak in ice thickness (calculated as Volume/area) has shifted significantly earlier.
It is also clear from crandles' post that if you calculate ice thickness as Volume/extent that the shift is much reduced, but still there.

What I would like to explore is where that shift came from.

For that, imagine an Arctic at the max with 10 M km^2 of FYI, and 10 M km^2 of thick MYI.
During the melting season, that FYI will melt out, while the thick MYI remains less affected.
So the average thickness of the ice during the melting season will actually increase.
The peak thickness will thus be in September, just as your chart shows.

Now imagine an Arctic with very little MYI. Just 10 M km^2 of FYI, which is melting out during the melting season. The average thickness for that Arctic will thus peak in the beginning of the melting season, around March.

I think that that effect (less MYI left over) is at the core of why you see an earlier thickness peak.
What do you think ?

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1635 on: April 27, 2017, 11:10:33 AM »
Rob, I hope I got the right place.  here is everything in somewhat chronological order.  Hope I got the overall gist of what was wanted . . .

Repost of what was original posted in "melting season".

Question:  I have used the PIOMAS volume and NSIDC area monthly averages to calculate thickness. 


As you already know dj, Wipneus has said that the NSIDC numbers have a "pole hole". This applies only to area, as they already incorporate the hole size into extent values. (i.e. it is taken as read that there is ice of >15% concentration at the pole hole hole.)

If one wishes to apply a correction to the area values, the relevant offsets are given here...
http://nsidc.org/data/docs/noaa/g02135_seaice_index/#pole-hole-size

Richard Rathbone

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Re: Latest PIOMAS update (April)
« Reply #1636 on: April 27, 2017, 01:19:27 PM »
Thanks, dj.
It is clear from your post that the peak in ice thickness (calculated as Volume/area) has shifted significantly earlier.
It is also clear from crandles' post that if you calculate ice thickness as Volume/extent that the shift is much reduced, but still there.

What I would like to explore is where that shift came from.

For that, imagine an Arctic at the max with 10 M km^2 of FYI, and 10 M km^2 of thick MYI.
During the melting season, that FYI will melt out, while the thick MYI remains less affected.
So the average thickness of the ice during the melting season will actually increase.
The peak thickness will thus be in September, just as your chart shows.

Now imagine an Arctic with very little MYI. Just 10 M km^2 of FYI, which is melting out during the melting season. The average thickness for that Arctic will thus peak in the beginning of the melting season, around March.

I think that that effect (less MYI left over) is at the core of why you see an earlier thickness peak.
What do you think ?

Yup. Its a consequence of thick MYI vanishing.

The average thickness development has two competing effects, all ice thins, which tends to reduce thickness, and the thinnest area melts out, which tends to increase thickness. When a lot of the volume was in thick ice the second effect dominated, and the peak was at minimum area. Now volume is a lot more evenly spread and peak thickness is close to maximum volume.

crandles

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Re: Latest PIOMAS update (April)
« Reply #1637 on: April 27, 2017, 03:55:19 PM »

It is clear from your post that the peak in ice thickness (calculated as Volume/area) has shifted significantly earlier.
It is also clear from crandles' post that if you calculate ice thickness as Volume/extent that the shift is much reduced, but still there.

Well actually, what I have been tring to say is that there are two peaks.
Using Wipneus area and finding Jan to 31 jul peak and also 1Aug to 31 Dec peak, I get:

3.092361804   1979 207  21.281
3.128831497   1979 230  17.996
3.036558828   1980 205  20.931
3.032874754   1980 215  19.230
2.802673201   1981 208  17.534
2.827039146   1981 218  15.775
2.503914211   1982 176  24.171
2.620895658   1982 255  13.400
2.860465965   1983 201  20.703
2.834102544   1983 245  15.186
2.908341814   1984 190  22.284
3.090239468   1984 256  14.500
3.159945094   1985 209  18.129
3.101037998   1985 213  17.471
2.92154531   1986 200  21.236
2.936283655   1986 225  17.430
3.044844646   1987 206  20.166
3.016573892   1987 221  17.298
2.96417511   1988 206  19.161
2.989685742   1988 219  17.022
2.819695352   1989 200  20.281
3.010469726   1989 254  14.666
2.946993494   1990 200  18.785
2.952489574   1990 264  13.759
2.971922926   1991 193  20.635
3.020591297   1991 261  13.490
2.859749842   1992 202  19.670
2.949292771   1992 243  14.999
2.88542031   1993 191  19.740
2.73732818   1993 229  13.186
2.846941741   1994 196  19.991
2.967926293   1994 224  15.029
2.765426222   1995 200  16.407
2.612161264   1995 220  13.039
2.576331873   1996 185  21.667
2.596124209   1996 251  13.746
2.940792488   1997 206  17.232
2.833314658   1997 223  14.691
2.81055007   1998 201  17.440
2.775820448   1998 217  14.485
2.837047931   1999 182  21.757
2.749647039   1999 220  13.964
2.755376398   2000 182  20.785
2.616035427   2000 245  11.093
2.83031532   2001 202  16.783
2.708392504   2001 215  14.571
2.650614194   2002 197  17.019
2.695923739   2002 214  13.673
2.688218718   2003 184  19.353
2.493603879   2003 214  12.844
2.476061308   2004 183  19.476
2.415927938   2004 213  13.326
2.496950185   2005 191  16.399
2.490413855   2005 227  10.671
2.45932977   2006 169  20.488
2.335210146   2006 214  11.688
2.333668324   2007 172  17.813
2.342022239   2007 230   7.269
2.379133233   2008 173  19.387
2.504845221   2008 225   9.374
2.172280361   2009 153  22.147
2.028605291   2009 216   9.330
2.079175679   2010 176  14.666
1.649473401   2010 214   7.147
1.99884714   2011 146  20.088
1.696375421   2011 213   6.882
2.028808358   2012 165  16.329
1.787574146   2012 219   5.693
1.994332988   2013 167  17.489
1.581658026   2013 216   7.458
2.042485784   2014 199  11.393
1.9535078   2014 252   6.987
2.164799525   2015 165  18.925
2.050185725   2015 219   7.906
2.093139502   2016 154  18.898
1.887173372   2016 239   5.001

The first peak is moving earlier from about 205 to 160 over 37 year so similar to vol/Extent just over a day earlier per year.

The second peak is possibly also moving earlier but has wild swings from time to time. 213 is the 1 Aug the first possible date for second peak the way I have done it. As it is often very close to 213 this suggests I haven't got the date right for splitting the peaks. So don't rely on those second peak dates.

Probably ought to graph the vol/Area numbers having got this far ....

crandles

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Re: Latest PIOMAS update (April)
« Reply #1638 on: April 27, 2017, 05:22:52 PM »
graph PIOMASVol/WipArea

Juan C. García

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Re: Latest PIOMAS update (April)
« Reply #1639 on: April 27, 2017, 07:58:42 PM »
The good news is that, according to Wipneus data, on April the area has not been decreasing fast. 2017 has 58 days being the lowest on area and 106 days among the 3 lowest, but on the last day that I evaluate (day 115, corresponding to April 25th on 2017) 2017 was on the 6th lowest. A little hope, but as of today, we haven't have a Beaufort Gyre like the one we had on April 2016.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1640 on: April 28, 2017, 12:22:53 AM »
This was originally posted on the 2017 Melting Season thread, but some parts are clearly of relevance to this PIOMAS thread...

...
Either way, and from the graphs posted earlier, it is clear that sea ice 'volume' is on a persistent and potentially catastrophic decline. 2017 is especially noteworthy, because of the current record low PIOMAS numbers.
...
We'll see what September 2017 brings us, but it seems clear that there is a good chance that we are about to find out if the Arctic summer melts ice 'volume' or if it melts 'extent'.

It's an interesting quandary, isn't it Rob?

I was playing about with the monthly figures for PIOMAS, NSIDC Area and NSIDC extent in order to see if I could tease out any clue as to which might be least susceptible to "noise". To do so, I used a simple linear regression in order to obtain a value for the trend, and then subsequently calculated the residuals.

I then compared the Standard Deviation of the residuals with the trend. It's obviously more than a bit crude and simplistic, but my thinking was the higher the value of this ratio, the less time it takes for the genuine underlying trend to emerge from any noise distortion (i.e. natural variability).

The September numbers were...

PIOMAS: Trend = -324 cubic kms per annum, SD of residuals = 1,434 cubic kms

NSIDC area: Trend = -79k sq kms per annum, SD of residuals = 441k sq kms

NSIDC extent: Trend = -87k sq kms per annum, SD of residuals = 550k sq kms


That produces ratios of...
PIOMAS 0.226
NSIDC area 0.18
NSIDC extent 0.159

A possibly more meaningful way of expressing these values might be in terms how many years worth of each trend equates to 2 times the relevant Standard Deviation (i.e. the old 95% confidence level). That comes out as 9 years, 11 years and 12 and a half years respectively.

Using that simplistic approach would suggest that PIOMAS will be the better indicator, as it makes an earlier emergence from the natural variability.

The PIOMAS Daily Arctic Ice Volume graph from Wipneus that you posted is excellent at showing how perilous the end-of-melt-season has become, but, looking at the March-April-May part, it also serves to show that we are still a long way from a totally ice free Arctic. On the 1979-2001 average, the value for the beginning of April is ~ 29,700 cubic kms. The equivalent 2017 value stands at ~ 20,4000 cubic kms - a drop of just over 9,000 cubic kms over a (notional) period of 27 years.

The attached diagrams below show PIOMAS projections for September and for the March-May average volume. If one projects a 2nd order polynomial trend line, the September figure effectively goes to zero in 5 years, but, with a linear projection, this is delayed until about 2032.

The maximum volume is typically attained in April, but with the March-May average and using a 2nd order polynomial fit, the trend does not go to zero until 2050. In fact, the March-May average would still be around 10,000 cubic kms in 20 years time. (Using a linear fit, this trend does not reach zero until almost the end of the 21st Century.)

Anyway, getting back to the melting season aspects, we both know how poor the correlation is for area/extent when the interval gets more than a couple of months. There are various references in the scientific literature to a decorrelation period of just 2 or 3 months for area/extent.

However, using Excel's CORREL, the correlation coefficient between the PIOMAS mean March-April-May residuals and the September residuals (1979-2016) comes out at an interesting 0.65

Rob, I know you asked a follow-up question, but I've been out virtually all day. I'm feeling zonked at the moment, but will provide an answer tomorrow.

There is one "significant" point that I should have mentioned in the original post. There were 38 pairs of values used to generate that correlation coefficient quoted just above. That means the system has, I think, 36 degrees of freedom. Using my old stats workbook, and given that d.f.=36, the generated correlation is established to hold at beyond the 0.001 significance level.

dj

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Re: Latest PIOMAS update (April)
« Reply #1641 on: April 28, 2017, 03:28:02 PM »
Thanks, dj.
It is clear from your post that the peak in ice thickness (calculated as Volume/area) has shifted significantly earlier.
It is also clear from crandles' post that if you calculate ice thickness as Volume/extent that the shift is much reduced, but still there.

What I would like to explore is where that shift came from.

For that, imagine an Arctic at the max with 10 M km^2 of FYI, and 10 M km^2 of thick MYI.
During the melting season, that FYI will melt out, while the thick MYI remains less affected.
So the average thickness of the ice during the melting season will actually increase.
The peak thickness will thus be in September, just as your chart shows.

Now imagine an Arctic with very little MYI. Just 10 M km^2 of FYI, which is melting out during the melting season. The average thickness for that Arctic will thus peak in the beginning of the melting season, around March.

I think that that effect (less MYI left over) is at the core of why you see an earlier thickness peak.
What do you think ?

I was thinking the same. 
But have not had the time to crudely crunch any numbers.
end of the yer (school term) has me busy ATM.  So I don't have much time available at the moment, but definitely would like to explore this a bit more.

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1642 on: April 28, 2017, 08:11:01 PM »
However, using Excel's CORREL, the correlation coefficient between the PIOMAS mean March-April-May residuals and the September residuals (1979-2016) comes out at an interesting 0.65

R=0.65 is not bad at all for a March predictor of September SIE.
But what is the SD over the residuals ? And is it better than the SD of 550 k km^2 from the simple linear trend ?
Either way, we should probably take this discussion elsewhere.
You want to take it to the PIOMAS thread ?

Rob, here are the (hopefully) relevant numbers from my PIOMAS spreadsheet. Please let me know if I have managed to misinterpret your question.    :-[

March 1979-2016
Equation of linear trend: Y = -0.264X + 31.921
Mean value = 26.781
SD of residuals (after detrending using the above linear trend) = 1.049
Correlation Coefficient with Sept 1979-2016 = 0.638

April 1979-2016
Equation of linear trend: Y = -0.263X + 32.926
Mean value = 27.805
SD of residuals (after detrending using the above linear trend) = 1.010
Correlation Coefficient with Sept 1979-2016 = 0.650

Average across March, April and May 1979-2016
Equation of linear trend: Y = -0.270X + 32.478
Mean value = 27.209
SD of residuals (after detrending using the above linear trend) = 1.038
Correlation Coefficient with Sept 1979-2016 = 0.692

September 1979-2016
Equation of linear trend: Y = -0.324X + 17.482
Mean value = 11.170
SD of residuals (after detrending using the above linear trend) = 1.434


{With the exception of the coefficients, which are dimensionless natural numbers, all the other values shown above should be expressed in thousands of cubic kms.}

NB In my early post, I wrongly gave the Mar-May correlation with Sept as 0.650. This was a transcription error, and that value (0.650) is actually the April:September correlation coefficient. The averaged (March-May):September correlation comes out at 0.692, as shown immediately above.


Given the Degrees of Freedom for those correlation figures, the p-value for each would be < 0.001, and by a substantial margin.

I hardly need to tell you (although some others might not be as numerate) but there would need to be some appropriate form of normalisation required in order to compare the PIOMAS and NSIDC residuals. However, the fact that the September residuals are larger than those from near the maximum volume period, even before any normalisation based on mean values, is indicative of the increased level of "noise" surrounding the annual minimum.



Rob Dekker

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Re: Latest PIOMAS update (April)
« Reply #1643 on: April 29, 2017, 08:16:29 AM »
Thanks Bill !
I appreciate your overview of the numbers, and I have a question.
When you write "Correlation Coefficient with Sept 1979-2016" do you mean correlation between PIOMAS in April and PIOMAS Sept 1979-2016 ? Or Between PIOMAS in April and NSIDC SIE 1979-2016 ?

What I thought you were calculating (with that R=0.65 number) was the correlation between PIOMAS in April regressed against NSIDC SEI in September.
Basically using PIOMAS in April as a 'predictor' for SIE in September.
And consequently I was interested if in that regression the SD of the residuals is better or worse than the SD of 550 k km^2 if we use 'time' as a predictor (prediction using a linear trend).

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1644 on: April 29, 2017, 09:56:26 AM »
Here you go, Rob...

April:September correlation coefficients for the period 1979-2016

Using NSIDC SIE monthly values only = -0.109

Using PIOMAS monthly values only = +0.650

Using PIOMAS April: NSIDC SIE September = +0.342


Given the Degrees of Freedom, that {PIOMAS April: NSIDC SIE September} correlation still has a p-value <0.05.

In other words, although the correlation could hardly be described as strong, it's still significant at the 95% confidence level.


{EDIT: Just to be fully explicit, the above correlations are based on the residuals left after each data series was detrended. In each case, the detrending was done by using a bog-standard linear trend line.}
« Last Edit: April 29, 2017, 03:13:14 PM by Bill Fothergill »

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1645 on: April 29, 2017, 03:22:06 PM »
Just for a giggle, I did a quick correlation analysis between the PIOMAS September residuals and the NSIDC SIE September residuals. The value thus obtained for the correlation coefficient was +0.755

That value would be significant at the 99.9% level (p-value < 0.001) had there been only 16 data pairs, rather than the actual number, which was 38. Had there even been only 7 data pairs, such a correlation coefficient would have been significant at the 95% level.

Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1646 on: April 29, 2017, 03:59:57 PM »
I dont think that residual correlation is much as high as you claim, if i detrend both, i found only R^2= 0.11
« Last Edit: April 29, 2017, 04:08:34 PM by Random_Weather »

Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1647 on: April 29, 2017, 04:03:07 PM »
ah okay, soory my fault, see you talking about Sep, not April

Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1648 on: April 29, 2017, 04:12:54 PM »
To make clear, April Volume residuals not saying anything about extent residuals in september, here for 1979-2016


Same for May, just June/July/August have good correlation of residuals with september residuals, its because april and may not really matters, because the most important is summer times

gerontocrat

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Re: Latest PIOMAS update (April)
« Reply #1649 on: April 29, 2017, 04:28:57 PM »
"Wait small" (pidgin English). Only one week or so and we can feast on a freshly killed POIMAS monthly update.