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Author Topic: Sea Ice Extent around Antarctica  (Read 122563 times)

Bill Fothergill

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Re: Sea Ice Extent around Antarctica
« Reply #500 on: February 22, 2017, 07:59:22 PM »
Here's what the above latest developments mean in terms of the 5-day NSIDC Charctic.

I've zoomed to where the current action is, and I've filtered out most of the "noise" years. As usual, I've included 2016 & 2017 (natch), as well as what had been, until recently, the three years with the lowest mins - 1997, 1993 & 2011.

I've added 2013, 2014 & 2015 just to show the spread from highest <> lowest annual minimums.

I've also added 2006 and 1980, as, between them, these represent "lowest daily values" from about the 12th March onward. Another reason for some interest in 1980, is because that is when the lowest annual average occurred. (So far)

« Last Edit: February 22, 2017, 10:00:46 PM by Bill Fothergill »

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #501 on: February 23, 2017, 03:11:40 PM »
SH "NSIDC extent": -19k4k
SH "NSIDC area": -33.0k

Among the annual minimums area went up two places and is now 4th lowest.

Area
1 1993-02-26 1.248163
2 1984-02-27 1.509585
3 1996-02-25 1.535481
4 2017-02-22 1.556394
5 2000-02-18 1.561033
6 2006-03-04 1.565059


The area graph is attached.


Tigertown

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Re: Sea Ice Extent around Antarctica
« Reply #502 on: February 24, 2017, 05:39:40 AM »
For Feb. 23rd JAXA has posted 2,167,669 km2 for SIE around Antarctica.

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #503 on: February 24, 2017, 04:38:26 PM »
For Feb 23, NSIDC reports a new daily record low at 2,156 Mn km2. The 5-day average dropped to 2,192 Mn km2. The latter index might go even lower tomorrow unless a significant growth is seen. I believe that todays big drop is due to that a lot of the fragmented ice in Amundsen sea went below 15%. Wipneus might know if that was the case or not.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #504 on: February 24, 2017, 04:52:50 PM »
I believe that todays big drop is due to that a lot of the fragmented ice in Amundsen sea went below 15%. Wipneus might know if that was the case or not.

Well, the details are thus:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-02-23 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        260.8  -11.3  -193.7        1164.7   +3.5   -31.3
                Indian Ocean           West Pacific Ocean
        147.1   -0.0   -42.3         519.1  -26.7  +158.8
                    Ross Sea                        Total
         64.8   -4.2  -620.5        2156.5  -38.8  -729.0

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        144.0   -8.8  -118.4         958.0   -6.6   +55.5
                Indian Ocean           West Pacific Ocean
         73.7   -1.7   -24.1         300.3  -34.3   +83.5
                    Ross Sea                        Total
         26.2   -2.8  -334.9        1502.3  -54.1  -338.4



The biggest losses are in the West Pacific Ocean region.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #505 on: February 24, 2017, 05:20:12 PM »
The area losses also bring a new annual minimum, moving 2017 tot the second place where it will probably stay for quite a while.

Extent
1 2017-02-23 2.156456

Area
1 1993-02-26 1.248163
2 2017-02-23 1.502254
3 1984-02-27 1.509585
4 1996-02-25 1.535481



Also in the daily ranking area is second lowest after the remarkable 1993:

area SH
2011-02-23 1.702829
2006-02-23 1.664207
1992-02-23 1.641926
1999-02-23 1.635909
1981-02-23 1.625223
1997-02-23 1.613904
1984-02-23 1.607507
1996-02-23 1.579022
2017-02-23 1.502254
1993-02-23 1.291779

gerontocrat

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Re: Sea Ice Extent around Antarctica
« Reply #506 on: February 24, 2017, 05:28:20 PM »
Each time one thinks the melting is over, off we go again. SST anomalies at 70 degrees and north of that still quite impressive. One waits to see if refreezing will be late and slow  and then if it is but a burp or a real change down there.

Patience is a virtue but sorely tested.
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Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #507 on: February 24, 2017, 05:52:12 PM »
Last days that the minimums set are in March.

Extent has the latest: 6 March 1986, but the second latest extent was 27 Feb 1984, 1991 and 1997.

Area has two March dates: 2006-03-04 and 1981-03-03. Before that is the pack, 17-27 February.

Here are the sorted lists (1978 has only data from November and December):


SH EXTENT
30 1994-02-12 3.082862
25 2010-02-16 2.842209
27 1979-02-16 2.873193
10 2016-02-17 2.577755
37 2003-02-17 3.625715
11 2000-02-18 2.582475
23 2005-02-18 2.803882
35 2015-02-18 3.532464
3 1993-02-19 2.280783
13 1985-02-19 2.601560
16 1981-02-19 2.675476
19 2007-02-19 2.722703
34 2001-02-19 3.440951
38 2013-02-19 3.678996
6 2006-02-20 2.486597
17 2002-02-20 2.696900
18 1999-02-20 2.707231
20 1989-02-20 2.722912
29 1987-02-20 2.996257
32 2004-02-20 3.259284
39 2008-02-20 3.691767
36 2014-02-21 3.548484
4 2011-02-22 2.318847
15 2009-02-22 2.670964
22 1990-02-22 2.784345
26 1982-02-22 2.863992
1 2017-02-23 2.156456
7 1992-02-23 2.492393
24 1983-02-23 2.816138
31 2012-02-23 3.111095
14 1988-02-24 2.638617
33 1995-02-24 3.329888
8 1980-02-25 2.516067
12 1996-02-25 2.597335
21 1998-02-25 2.771514
2 1997-02-27 2.264152
5 1984-02-27 2.381731
9 1991-02-27 2.553553
28 1986-03-06 2.952849
40 1978-12-31 7.283008
SH AREA
37 2015-02-14 2.414870
17 1982-02-17 1.713860
18 2016-02-17 1.729589
30 1995-02-17 2.002174
5 2000-02-18 1.561033
32 1994-02-18 2.098845
9 1997-02-19 1.589288
10 1985-02-19 1.635733
25 2007-02-19 1.821313
35 2001-02-19 2.286595
38 2014-02-19 2.423633
13 2002-02-20 1.649281
27 1979-02-20 1.926174
29 2010-02-20 1.933016
34 2008-02-20 2.203494
36 2013-02-20 2.389945
26 1989-02-21 1.841981
22 2009-02-22 1.794061
31 1990-02-22 2.026988
33 2004-02-22 2.154999
2 2017-02-23 1.502254
11 1992-02-23 1.641926
28 2012-02-23 1.931870
16 1988-02-24 1.691611
21 1987-02-24 1.781372
4 1996-02-25 1.535481
19 1983-02-25 1.738279
23 1991-02-25 1.797485
24 2005-02-25 1.798750
1 1993-02-26 1.248163
7 1999-02-26 1.577058
14 1998-02-26 1.650298
15 2011-02-26 1.677629
3 1984-02-27 1.509585
12 1980-02-27 1.646186
20 1986-02-27 1.763319
39 2003-02-27 2.448344
8 1981-03-03 1.588790
6 2006-03-04 1.565059
40 1978-12-31 4.831456


DrTskoul

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Re: Sea Ice Extent around Antarctica
« Reply #508 on: February 24, 2017, 07:08:44 PM »
The area losses also bring a new annual minimum, moving 2017 tot the second place where it will probably stay for quite a while.

Extent
1 2017-02-23 2.156456

Area
1 1993-02-26 1.248163
2 2017-02-23 1.502254
3 1984-02-27 1.509585
4 1996-02-25 1.535481



Also in the daily ranking area is second lowest after the remarkable 1993:

area SH
2011-02-23 1.702829
2006-02-23 1.664207
1992-02-23 1.641926
1999-02-23 1.635909
1981-02-23 1.625223
1997-02-23 1.613904
1984-02-23 1.607507
1996-02-23 1.579022
2017-02-23 1.502254
1993-02-23 1.291779


Quite an interesting race...
“You can know the name of a bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird... So let's look at the bird and see what it's doing -- that's what counts.”
― Richard P. Feynman

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #509 on: February 25, 2017, 05:10:12 PM »
Another daily record low and another record low 5-day average. SIE for February 24 was down to 2,145 Mn km2 while the 5-day average was down to 2,180 Mn km2. While I've hard to imagine any further extent loss the next couple of days, the 5-day average might dip down depending on the next few days SIE.

What's interesting is that the University of Bremen sea ice graph still have 1993 as being the record low year in their graph. See the graph at: https://seaice.uni-bremen.de/data/amsr2/today/extent_s_running_mean_amsr2_regular.png

Andre

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Re: Sea Ice Extent around Antarctica
« Reply #510 on: February 25, 2017, 08:43:25 PM »
What's interesting is that the University of Bremen sea ice graph still have 1993 as being the record low year in their graph. See the graph at: https://seaice.uni-bremen.de/data/amsr2/today/extent_s_running_mean_amsr2_regular.png

I would guess that as long as it isnt clear, when the minimum will be reached this year and what the new record will be, they will wait to make any changes. Otherwise, they would have to update the record every day we see another SIE drop. Probably a lot easier to just wait a few weeks, make sure we are well past the minimum and then update the new record low number.

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #511 on: February 26, 2017, 02:56:49 PM »
Another daily record low, now down to 2,135 Mn km2 and a 5-day average moving down to 2,169 Mn km2... Any area changes today?

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #512 on: February 26, 2017, 05:23:47 PM »
. Any area changes today?

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-02-25 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        247.6   +4.4  -204.6        1176.2   +5.7   -28.0
                Indian Ocean           West Pacific Ocean
        139.8   -8.0   -47.2         504.9  -16.5  +144.4
                    Ross Sea                        Total
         66.2   +4.7  -645.6        2134.8   -9.8  -781.0

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        139.6   +0.4  -120.3         986.3  +24.7   +77.0
                Indian Ocean           West Pacific Ocean
         68.1   -5.7   -27.3         324.3   -7.5  +109.9
                    Ross Sea                        Total
         26.6   -0.4  -350.8        1544.9  +11.6  -311.4

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #513 on: February 27, 2017, 08:50:03 AM »
Todays sea ice map of Antarctica reveals some newly formed ice in the Ross Sea. I think this is it and that the final daily minimum will be 2,135 Mn km2. I expect a small uptick today.

However, it's possible that the 5-day average might go somewhat lower than yesterdays reported 2,169 Mn km2.

Finally, in case you haven't seen it, the thickness map that is easily found for the Arctic basin also exists for the Antarctica. There are two links: https://seaice.uni-bremen.de/data/smos/png/ It's also found at: https://seaice.uni-bremen.de/databrowser/

Here is the Antarctica thickness map for February 26: Courtesy to University of Bremen.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #514 on: February 27, 2017, 09:12:43 AM »
It is still a big continent. Extent and area calculated from Uni Hamburg SIC still dropping. New minimum for 2016 extent:

Regional Arctic Sea Ice Extent and Area calculated from Uni Hamburg ASI AMSR2 concentration data
See uh_am2_ant.txt for more details
Date: 2017-02-26 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                220.3  -10.5                1196.6   -0.7
                Indian Ocean           West Pacific Ocean
                147.3   -6.5                 435.4   -5.8
                    Ross Sea                        Total
                 84.5   +5.7                2084.2  -17.8

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                183.7   -6.4                1078.5   -7.6
                Indian Ocean           West Pacific Ocean
                121.6   -8.3                 371.5   -4.1
                    Ross Sea                        Total
                 62.3   +1.8                1817.5  -24.8

iceman

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Re: Sea Ice Extent around Antarctica
« Reply #515 on: February 27, 2017, 11:49:09 AM »
It is still a big continent. Extent and area calculated from Uni Hamburg SIC still dropping. ...

Amazing.  I was expecting an early minimum, following the wind-driven compaction earlier in the season.  Maybe accumulated insolation is still taking its toll.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #516 on: February 27, 2017, 01:54:24 PM »
NSIDC sees it slightly different:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-02-26 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        251.7   +4.1  -200.1        1179.2   +3.0   -30.3
                Indian Ocean           West Pacific Ocean
        144.1   +4.3   -42.3         513.4   +8.5  +152.0
                    Ross Sea                        Total
         71.6   +5.4  -657.4        2160.0  +25.3  -778.0

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        133.8   -5.8  -125.5         976.9   -9.4   +63.2
                Indian Ocean           West Pacific Ocean
         73.6   +5.5   -21.0         313.2  -11.1   +99.6
                    Ross Sea                        Total
         27.1   +0.5  -360.6        1524.6  -20.3  -344.3


NSIDC extent and area minimums did not change:

Extent
1 2017-02-25 2.134752

Area
1 1993-02-26 1.248163
2 2017-02-23 1.502254

Tigertown

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Re: Sea Ice Extent around Antarctica
« Reply #517 on: February 28, 2017, 04:43:29 AM »
For Feb. 27th JAXA has posted 2,152,483 km2 for SIE around Antarctica.

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #518 on: February 28, 2017, 08:24:18 AM »
Interesting TT! Todays map from UiB shows continued refreezing in Ross Sea. From Bremens graph it's a really tight race between 2017 and 1993 about the record. Should be another small uptick today from NSIDC given the newly formed ice in Ross Sea. Maybe other areas counteract these numbers by melting/compaction.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #519 on: February 28, 2017, 12:52:57 PM »
Maybe other areas counteract these numbers by melting/compaction.

Some do, resulting in very small net losses:

Regional Arctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-02-27 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                232.2   -7.5                1188.9  -22.2
                Indian Ocean           West Pacific Ocean
                148.5   +0.8                 448.9  +11.4
                    Ross Sea                        Total
                108.4  +15.3                2126.9   -2.3

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                190.8   -2.7                1070.5  -18.3
                Indian Ocean           West Pacific Ocean
                119.1   +0.6                 377.1   +8.4
                    Ross Sea                        Total
                 75.6   +7.6                1833.1   -4.3

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #520 on: February 28, 2017, 01:53:26 PM »
A second opinion from NSIDC data:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-02-27 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        216.8  -34.9  -235.5        1181.1   +1.9   -34.9
                Indian Ocean           West Pacific Ocean
        142.3   -1.8   -44.1         494.0  -19.4  +131.5
                    Ross Sea                        Total
         74.9   +3.3  -672.9        2109.1  -50.9  -855.9

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        131.1   -2.8  -128.3         980.5   +3.6   +61.0
                Indian Ocean           West Pacific Ocean
         73.3   -0.3   -20.7         299.8  -13.4   +86.5
                    Ross Sea                        Total
         26.6   -0.5  -373.0        1511.2  -13.3  -374.4


Extent sets a new lower minimum.

oren

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Re: Sea Ice Extent around Antarctica
« Reply #521 on: February 28, 2017, 05:50:39 PM »
Wow. Still not over  :o

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #522 on: February 28, 2017, 06:25:48 PM »
No Oren, the fat lady hasn't sung yet :) But I would be extremely surprised if we dipped below 2 Mn km2 at this time of year. Depending on the weather conditions the next few days it's possible that the 5-day average may reach its minimum March, something that's not too common.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #523 on: March 01, 2017, 08:13:42 AM »
It is going to be a late minimum according to sea ice concentration data from Uni Bremen:


Regional Antarctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-02-28 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                223.1  -10.1                1199.1   +8.2
                Indian Ocean           West Pacific Ocean
                151.1   +1.1                 429.1  -21.3
                    Ross Sea                        Total
                 98.3  -10.7                2100.8  -32.8

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                184.3   -7.1                1082.4  +10.2
                Indian Ocean           West Pacific Ocean
                122.9   +2.8                 367.1  -11.3
                    Ross Sea                        Total
                 70.3   -5.7                1827.1  -11.1

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #524 on: March 01, 2017, 09:05:55 AM »
Wipneus: do you know if the extent value from Uni Bremen lower than the minimum back in 1993 and 1997 was?

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #525 on: March 01, 2017, 10:08:16 AM »
Wipneus: do you know if the extent value from Uni Bremen lower than the minimum back in 1993 and 1997 was?

The data from Uni Bremen that I use is AMSR2, so only since mid July 2012.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #526 on: March 01, 2017, 10:35:42 AM »
The only other (besides NSIDC) time series that I have going that far back is from IFREMER (French Research Institute for Exploitation of the Sea). It is using the ASI algorithm, so higher resolution and as different as can be. Available since 1992.

But, the IFREMER data says basically the same as NSIDC: extent in 2017 is significantly lower (200k-300k) than any other year. Only 1993 area is lower than 2017 (by 200k or so).

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #527 on: March 01, 2017, 01:59:23 PM »
NSIDC sees very small changes that could well be reversed with the update tomorrow:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-02-28 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        221.2   +4.5  -232.3        1181.5   +0.4   -42.4
                Indian Ocean           West Pacific Ocean
        146.0   +3.7   -40.7         489.9   -4.1  +126.2
                    Ross Sea                        Total
         70.2   -4.7  -699.8        2109.0   -0.1  -889.0

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        131.3   +0.2  -128.8         981.2   +0.7   +54.2
                Indian Ocean           West Pacific Ocean
         74.7   +1.4   -18.9         299.4   -0.4   +86.4
                    Ross Sea                        Total
         25.8   -0.8  -387.7        1512.4   +1.1  -394.8

iceman

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Re: Sea Ice Extent around Antarctica
« Reply #528 on: March 01, 2017, 03:02:04 PM »
NSIDC sees very small changes that could well be reversed with the update tomorrow:
   ....
If the extent number stands, that would make 2017 second-latest by the thinnest of margins (per your sorted list in post #507 upthread).
     Quite a reversal from 2015, which was the fourth-earliest on record.
« Last Edit: March 02, 2017, 04:00:58 PM by iceman »

Andre

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Re: Sea Ice Extent around Antarctica
« Reply #529 on: March 02, 2017, 06:53:25 AM »
March 1st, JAXA reporting 2,147,345 km2. Another small drop and a new record low.


Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #530 on: March 02, 2017, 09:03:00 AM »
Area/extent calculated from Uni Bremen's sea ice concentration reach new lows :

Regional Antarctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-03-01 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                223.6   -0.9                1197.4   -2.8
                Indian Ocean           West Pacific Ocean
                131.7  -20.5                 446.7  +15.8
                    Ross Sea                        Total
                102.8   +3.3                2102.1   -5.1

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                183.2   -2.0                1064.0  -19.2
                Indian Ocean           West Pacific Ocean
                109.1  -14.5                 379.9  +11.3
                    Ross Sea                        Total
                 69.8   -1.4                1806.0  -25.8

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #531 on: March 02, 2017, 09:23:27 AM »
interesting Wipneus! :) Let's see if NSIDC also comes up with a new record low value today!

If the NSIDC minimum (5-day avg) is occurring now in March it will only be the fifth time this happens. The earlier occurrences are: 1986 (March 6), 2003 (March 3), 1991 (March 2) and 1980 (March 1). The case from 1980 doesn't contain the value for the leap day. In 1986, the values were also given for every second day but the minimum then was so late that there can be no doubts it was absolutely the latest such and occurred in March.

Daily NSIDC values from the ftp adress are available from August 1987. ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/south/daily/data/S_seaice_extent_daily_v2.1.csv

I hope I haven't got something wrong here!

johnm33

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Re: Sea Ice Extent around Antarctica
« Reply #532 on: March 02, 2017, 11:18:24 AM »
Feb. anomoly from http://nsidc.org/data/bist/bist.pl?annot=1&legend=1&scale=100&tab_cols=2&tab_rows=2&config=seaice_index&submit=Refresh&mo0=01&hemis0=S&img0=anom&mo1=02&hemis1=S&img1=anom&year0=2017&year1=2016

+ yesterdays image from http://www.seaice.dk/latest/yesterdays-amsr2-s-mos.jpg click the link for a more detailed image [this will change daily]

I'm beggining to wonder if these small daily losses will stretch towards the equinox, or even beyond. There may be just enough circulation of waters by the coast to inhibit freezing, and without ice cover to dampen waves much too much turbulence.

crandles

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Re: Sea Ice Extent around Antarctica
« Reply #533 on: March 02, 2017, 01:35:42 PM »
So statistically indistinguishable from latest minimum on record for both JAXA and NSIDC daily because the shape of the minimum in 1986 means the minimum might have occurred on 29th Feb, 1st March or 2nd of March (3rd also possible but seems unlikely)

2.075 on daily NSIDC is new low as is 2147345 for JAXA.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #534 on: March 02, 2017, 01:45:13 PM »
On both extent and area:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-03-01 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        217.5   -3.7  -232.3        1185.5   +4.0   -49.8
                Indian Ocean           West Pacific Ocean
        109.4  -36.6   -76.4         496.6   +6.7  +129.2
                    Ross Sea                        Total
         65.8   -4.4  -730.5        2074.9  -34.0  -959.7

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        128.6   -2.6  -128.5         982.9   +1.7   +43.8
                Indian Ocean           West Pacific Ocean
         56.1  -18.6   -37.1         298.5   -0.9   +83.7
                    Ross Sea                        Total
         22.9   -3.0  -407.9        1489.0  -23.4  -445.9

gerontocrat

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Re: Sea Ice Extent around Antarctica
« Reply #535 on: March 02, 2017, 03:49:05 PM »
So statistically indistinguishable from latest minimum on record for both JAXA and NSIDC daily because the shape of the minimum in 1986 means the minimum might have occurred on 29th Feb, 1st March or 2nd of March (3rd also possible but seems unlikely)

2.075 on daily NSIDC is new low as is 2147345 for JAXA.

By coincidence I have just asked on stupid questions what is the accuracy of these measurements. Down to 1km2 or even 1000km2 obviously spurious accuracy ?
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crandles

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Re: Sea Ice Extent around Antarctica
« Reply #536 on: March 02, 2017, 05:12:47 PM »
So statistically indistinguishable from latest minimum on record for both JAXA and NSIDC daily because the shape of the minimum in 1986 means the minimum might have occurred on 29th Feb, 1st March or 2nd of March (3rd also possible but seems unlikely)

2.075 on daily NSIDC is new low as is 2147345 for JAXA.

By coincidence I have just asked on stupid questions what is the accuracy of these measurements. Down to 1km2 or even 1000km2 obviously spurious accuracy ?

That is a more difficult question than my simplistic we just don't know when 1986 minimum was due to reporting only every other day.

The curves look quite smooth for SH compared to NH, which suggests that the uncertainty of the date of minimum is not all that high but yes 1000km2 accuracy does not seem likely. Sorry that isn't much of an answer.

Lord M Vader

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Re: Sea Ice Extent around Antarctica
« Reply #537 on: March 02, 2017, 06:17:15 PM »
In a "best case scenario" we might have 1-2 days with even lower values due to intrusion of warm waters and compaction. As we already are lowest on record, I tink it would be "exciting" if we could bottom out at 1,99 Mn km2. That would require another 76K drop.

But given the unusually low extent from November and onward we can be pretty sure that tremendeous amounts of heat have entered into the Southern Ocean this melting season. Even if the refreezing is imminent the damage is already done. And I won't be surprised if we are going to see some decent polar amplification by March-April around Antarctica.

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #538 on: March 02, 2017, 06:41:33 PM »
(...) what is the accuracy of these measurements. Down to 1km2 or even 1000km2 obviously spurious accuracy ?

I would rather not call these measurements. The satellite sensor measures microwave brightness's. These are inputs to a calculation (perhaps involving other inputs) that delivers sea ice concentration on a grid with a certain cell size. Sometimes it stops there, sometimes extent is calculated (possibly with more corrections). In only a few cases area is calculated.

The first step, satellite measurements, have error levels specified.
The second only in a few cases. Jaxa is close to 10%, ASI (Hamburg, Bremen) may be 15%. Figures from the top of my head.
I cannot remember seeing extent or even area accuracy being estimated. Full error bars would probably measured in 100,000's of sqkm. Mostly systematic (gridsize etc.) , some part random noise.

The day-to-day changes (sticking to one calculation e.g. Jaxa) will  be more reliable. Maybe a just a few k in case of the Antarctic minimum as crandles observed.
With this in mind, I think the conclusion that the minimum can be called "rather late" is robust (with the possibility that it may later become "very late").

For year to year comparisons you need a time series that has been carefully compiled for this purpose. Only NSIDC can really be used. The IFREMER series uses the same satellite sensors as NSIDC (but other microwave bands) is available since 1992. From those I would say that lowest extent minimum since 1979 seems also robust. 1993 seems an odd year as it has a relatively very low area minimum but not by extent.

gerontocrat

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Re: Sea Ice Extent around Antarctica
« Reply #539 on: March 02, 2017, 08:16:29 PM »
Hullo ASIF Guv'nor. I actually engaged brain to read the notes on Jaxa. Confirms up to 10 % error on SIC data. BUT !
In statistics often an individual datum can have a very high error. But when enough bits of data are brought together the error of the sum of the entire data is reduced to virtualy zero.

I find it hard to believe that the current Jaxa measurement of Antarctic SIE is 2147 km2 '000 +/- 10 %. As they say - I think we need to know.
"Para a Causa do Povo a Luta Continua!"

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #540 on: March 03, 2017, 08:23:36 AM »
Increases in the Bremen sea ice concentration grids

Regional Antarctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-03-02 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                238.8  +13.9                1238.0  +39.2
                Indian Ocean           West Pacific Ocean
                128.0   -5.0                 456.6   +8.4
                    Ross Sea                        Total
                 81.1  -22.1                2142.5  +34.4

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                192.9   +8.8                1095.6  +30.7
                Indian Ocean           West Pacific Ocean
                104.8   -5.3                 382.6   +1.5
                    Ross Sea                        Total
                 57.9  -12.2                1833.8  +23.5
.


Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #541 on: March 03, 2017, 08:36:34 AM »

I find it hard to believe that the current Jaxa measurement of Antarctic SIE is 2147 km2 '000 +/- 10 %.

Nobody that I know of says so. Extent calculation makes that grid cells with concentration > 25% or < 5% will have no (zero) error. In the marginal zone ( 5%<sic<25%) random errors will cancel out, but systematic (too low or too high values ) won't. Especially in the Arctic false coastal ice is surprisingly large ( my coastal correction today in UH calculation is 262k extent and 157k area).

Bill Fothergill

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Re: Sea Ice Extent around Antarctica
« Reply #542 on: March 03, 2017, 11:24:20 AM »
So statistically indistinguishable from latest minimum on record for both JAXA and NSIDC daily because the shape of the minimum in 1986 means the minimum might have occurred on 29th Feb, 1st March or 2nd of March (3rd also possible but seems unlikely)

2.075 on daily NSIDC is new low as is 2147345 for JAXA.

By coincidence I have just asked on stupid questions what is the accuracy of these measurements. Down to 1km2 or even 1000km2 obviously spurious accuracy ?

This very valid question is at least partially addressed by the NSIDC in their FAQ section.

https://nsidc.org/arcticseaicenews/faq/#error_bars

The relevant bit reads as follows...

"We estimate error based on accepted knowledge of the sensor capabilities and analysis of the amount of “noise,” or daily variations not explained by changes in weather variables. For average relative error, or error relative to other years, the error is approximately 20,000 to 30,000 square kilometers (7,700 to 11,600 square miles), a small fraction of the total existing sea ice. For average absolute error, or the amount of ice that the sensor measures compared to actual ice on the ground, the error is approximately 50 thousand to 1 million square kilometers (19,300 to 386,100 square miles), varying over the year. During summer melt and freeze-up in the fall, the extent may be underestimated by 1 million square miles; during mid and late winter before melt starts, the error will be on the low end of the estimates. It is important to note that while the magnitude of the error varies through the year, it is consistent year to year. This gives scientists high confidence in interannual trends at a given time of year.

The absolute error values may seem high, but it is important to note that each year has roughly the same absolute error value, so the decline over the long term remains clear. NSIDC has high confidence in sea ice trend statistics and the comparison of sea ice extent between years."

gerontocrat

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Re: Sea Ice Extent around Antarctica
« Reply #543 on: March 03, 2017, 12:00:14 PM »
So statistically indistinguishable from latest minimum on record for both JAXA and NSIDC daily because the shape of the minimum in 1986 means the minimum might have occurred on 29th Feb, 1st March or 2nd of March (3rd also possible but seems unlikely)

2.075 on daily NSIDC is new low as is 2147345 for JAXA.

By coincidence I have just asked on stupid questions what is the accuracy of these measurements. Down to 1km2 or even 1000km2 obviously spurious accuracy ?

This very valid question is at least partially addressed by the NSIDC in their FAQ section.

https://nsidc.org/arcticseaicenews/faq/#error_bars

The relevant bit reads as follows...

"We estimate error based on accepted knowledge of the sensor capabilities and analysis of the amount of “noise,” or daily variations not explained by changes in weather variables. For average relative error, or error relative to other years, the error is approximately 20,000 to 30,000 square kilometers (7,700 to 11,600 square miles), a small fraction of the total existing sea ice. For average absolute error, or the amount of ice that the sensor measures compared to actual ice on the ground, the error is approximately 50 thousand to 1 million square kilometers (19,300 to 386,100 square miles), varying over the year. During summer melt and freeze-up in the fall, the extent may be underestimated by 1 million square miles; during mid and late winter before melt starts, the error will be on the low end of the estimates. It is important to note that while the magnitude of the error varies through the year, it is consistent year to year. This gives scientists high confidence in interannual trends at a given time of year.

The absolute error values may seem high, but it is important to note that each year has roughly the same absolute error value, so the decline over the long term remains clear. NSIDC has high confidence in sea ice trend statistics and the comparison of sea ice extent between years."


So it is the trend that matters as if there is error it is consistent. It is just as well the trolls are pretty dumb. The potential for misinformation is high.


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Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #544 on: March 03, 2017, 04:48:02 PM »
Also NSIDC sees more ice:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-03-02 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        230.2  +12.7  -221.5        1204.5  +19.0   -44.4
                Indian Ocean           West Pacific Ocean
        106.4   -3.1   -84.2         501.5   +4.8  +127.1
                    Ross Sea                        Total
         68.4   +2.6  -752.4        2111.0  +36.1  -975.4

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        120.4   -8.3  -138.5        1002.3  +19.3   +51.1
                Indian Ocean           West Pacific Ocean
         51.7   -4.4   -43.5         293.7   -4.8   +76.3
                    Ross Sea                        Total
         23.2   +0.4  -424.6        1491.2   +2.2  -479.2

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #545 on: March 04, 2017, 08:55:55 AM »
Not a very convincing start of the refreezing season, according to Bremen AMSR2 data:

Regional Antarctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-03-03 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                229.5   -9.9                1242.8   +2.5
                Indian Ocean           West Pacific Ocean
                129.9   +0.3                 435.7  -22.4
                    Ross Sea                        Total
                 92.2  +10.5                2130.1  -19.0

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                186.1   -7.2                1120.8  +23.3
                Indian Ocean           West Pacific Ocean
                107.2   +1.2                 366.1  -17.9
                    Ross Sea                        Total
                 64.1   +5.8                1844.2   +5.3

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #546 on: March 04, 2017, 02:27:26 PM »
NSIDC show increases, but slow compared with most other years.

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-03-03 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        213.1  -17.1  -244.4        1230.9  +26.4   -30.2
                Indian Ocean           West Pacific Ocean
        103.8   -2.5   -89.7         498.3   -3.1  +124.5
                    Ross Sea                        Total
         79.4  +11.0  -769.6        2125.6  +14.6 -1009.3

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        112.2   -8.2  -150.8        1017.7  +15.4   +55.9
                Indian Ocean           West Pacific Ocean
         50.2   -1.5   -45.7         284.8   -8.9   +68.0
                    Ross Sea                        Total
         26.6   +3.4  -442.2        1491.5   +0.3  -514.7

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #547 on: March 05, 2017, 07:19:29 AM »
Small drops according to Bremen data:

Regional Antarctic Sea Ice Extent and Area calculated from Uni Bremen ASI AMSR2 concentration data
See ub_am2_3.125_ant.txt for more details
Date: 2017-03-04 12:00  Values in 1000 km^2

Extent (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                224.7   -6.3                1241.1   -3.8
                Indian Ocean           West Pacific Ocean
                133.9   +3.3                 426.4  -11.0
                    Ross Sea                        Total
                109.8  +16.9                2135.9   -0.9

Area (value, one day change):
Bellingshausen&Amundsen Seas                   Weddel Sea
                180.3   -6.6                1119.5   -2.9
                Indian Ocean           West Pacific Ocean
                108.9   +1.2                 359.2   -8.2
                    Ross Sea                        Total
                 72.8   +8.1                1840.7   -8.4

Wipneus

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Re: Sea Ice Extent around Antarctica
« Reply #548 on: March 05, 2017, 02:29:57 PM »
NSIDC sea ice concentration shows some small changes too:

Regional Antarctic Sea Ice Extent and Area calculated from NSIDC NASA Team concentration data
Date: 2017-03-04 12:00  Values in 1000 km^2

Extent (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        226.3  +13.2  -237.1        1226.6   -4.3   -43.9
                Indian Ocean           West Pacific Ocean
        103.7   -0.2   -92.3         491.2   -7.2  +112.7
                    Ross Sea                        Total
         93.0  +13.5  -784.8        2140.7  +15.1 -1045.5

Area (value, one day change, anomaly):
Bellingshausen&Amundsen Seas                   Weddel Sea
        118.3   +6.2  -148.8         997.5  -20.1   +26.5
                Indian Ocean           West Pacific Ocean
         50.9   +0.7   -45.3         286.0   +1.1   +67.7
                    Ross Sea                        Total
         33.4   +6.8  -453.8        1486.1   -5.4  -553.6



The drop in area means a new minimum. The date, 4th March, is the latest on record, shared with 2006.

iceman

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Re: Sea Ice Extent around Antarctica
« Reply #549 on: March 05, 2017, 02:57:10 PM »
NSIDC sea ice concentration shows some small changes too:
   ....
Thanks for providing details on both series during this time.  Interesting to note there are day-to-day differences by region, though the regional deltas were more in agreement on 03-01 when extent hit its minimum.