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DavidR

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Re: 2015 sea ice area and extent data
« Reply #50 on: February 24, 2015, 09:26:40 PM »
Thanks for the replies.  :D

I agree a trend would seem more likely than a step change. Perhaps there could be a trend with 81, 84 and 85 being unusually high by chance. But if it doesn't look like a trend then correlation with something might be a better possibility than a step change?

The earlier maximums at the start of the period don't surprise me as, from a trend perspective, it's sea temperature and insolation that will stop expansion. The greater ice extent at the start of the period require it to be further south and thus exposed to  insolation, and consequent  sea warming, earlier.
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epiphyte

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Re: 2015 sea ice area and extent data
« Reply #51 on: February 24, 2015, 10:00:22 PM »

Just random noise or is there likely to be an underlying cause, and if so what?

Crandles, I sent you a PM - but I've got a hunch it's the moon. I looked at a couple of years and, and at first sight both the periodicity of the peaks and the timing of the nearest spring tide w.r.t the peaks for each year seem roughly right?


crandles

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Re: 2015 sea ice area and extent data
« Reply #52 on: February 25, 2015, 01:11:08 AM »
I doubt I have been very precise with this so don't take it as gospel, but what I got for dates of 15 day binomial weighted average peak days was as follows:

No days after new/full moon, Frequency
0   1
1   1
2   2
3   8
4   1
5   2
6   3
7   4
8   1
9   4
10   5
11   0
12   2
13   2
   
____36

If the frequencies of 4 and 5 were next to the 8 it would be more convincing.

3 to 10 days later have 28 of 36 of the occurrences, which seems a high proportion for 8/14ths of the time but I think I did a bit of cherry picking in choosing that 3 to 10 days later period. 20.5 would be average and by choosing which period you are bound to be able to get a few more, so I doubt there is statistical significance there.

Maybe the 8 is more significant but I think more accuracy might be required. If 2 or 3 actually belonged to 2 or 4 days later rather than 3 then the distribution would look pretty flat.

Thus I am doubting there is much if any significance, but that doesn't prove there is no effect.

Maybe someone has a suitable test of significance to hand rather than relying on my judgement?

Peter Ellis

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Re: 2015 sea ice area and extent data
« Reply #53 on: February 25, 2015, 10:25:14 AM »
Is there a correlation between the day of the maximum and the magnitude of the maximum?

You could argue it either way - a longer freezing season might imply a later maximum (because it's a cold year, so stuff goes on freezing for longer), or it could imply an earlier maximum (a high maximum means more ice at lower latitudes, so melt will start sooner once the sun comes up).

Would be interesting to know if either of those is supported by the data.

You'll need to detrend the data for both the date of the maximum and the magnitude of the maximum, otherwise you may get a spurious correlation if both are changing over time for unrelated reasons.

crandles

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Re: 2015 sea ice area and extent data
« Reply #54 on: February 26, 2015, 01:37:09 PM »
Used 31 day average for magnitude and day of peak. Detrended, I got correlation of -0.108

Put the calculation here if you are interested or want to do more (like test for significance?):

https://docs.google.com/spreadsheets/d/1nY_gMHOpITIIw0OMo_nqZxvR0KufUw1oZlL8YD5T7m4/edit?usp=sharing

FWIW

The day trendline increases from day 64.4 to 71.6

I think the negative correlation is what I would expect. If the magnitude of the maximum is low then the ice is at high latitude and you have to wait longer for the sun to get high enough at the edge of the pack.

The alternative given "a longer freezing season might imply a later maximum" perhaps isn't quite what you meant, maybe 'a strong freezing season' might imply ... ?

If that is what you meant, strength of freezing season is mainly well before the peak and why should weather continue to be unusual in that direction rather than reverting to the mean?
« Last Edit: February 26, 2015, 01:50:36 PM by crandles »

Peter Ellis

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Re: 2015 sea ice area and extent data
« Reply #55 on: February 26, 2015, 02:36:24 PM »
Yeah, I meant a stronger freezing season.  I agree with you that I'd personally expect the weak negative correlation, but thought it was sufficiently arguable that I should present both options.

If you want a slightly more mechanistic version of it, you could say "Cold/warm weather conditions near the ice margins in March are likely to both increase/decrease the overall maximum and also prolong/shorten the melting season. This means you expect longer freezing seasons to correlate positively with higher maxima."

crandles

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Re: 2015 sea ice area and extent data
« Reply #56 on: February 26, 2015, 03:09:12 PM »
Not sure I really like your

If you want a slightly more mechanistic version of it, you could say "Cold/warm weather conditions near the ice margins in March are likely to both increase/decrease the overall maximum and also prolong/shorten the melting season. This means you expect longer freezing seasons to correlate positively with higher maxima."

Cold weather certainly will mean a late maximum but IMHO that might have very little affect on the area at maximum. It may have a strong effect on (peak area - area on say 15 Feb) but that isn't all that important to the peak area. I don't know if there is some sophisticated analysis possible there - tease out the effect of cold weather causing a late peak, adjust for that and then show a strong negative correlation between detrended maximum and date of maximum as adjusted for weather?


Steven

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Re: 2015 sea ice area and extent data
« Reply #57 on: February 26, 2015, 09:23:33 PM »
Used 31 day average for magnitude and day of peak. Detrended, I got correlation of -0.108
...
I think the negative correlation is what I would expect.

The correlation seems to be very weak.  In fact, it turns out that the sign of the correlation coefficient depends on the fact that you used 31-day averages.

E.g., using 15-day (rather than 31-day) simple moving averages, the correlation between the day of the maximum and the magnitude of the maximum is weakly positive, +0.09, if both time series are detrended.

So depending on how the maximum is calculated, you can obtain a weak negative or a weak positive correlation.
« Last Edit: February 26, 2015, 11:11:52 PM by Steven »

jdallen

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Re: 2015 sea ice area and extent data
« Reply #58 on: February 27, 2015, 12:27:32 AM »
Used 31 day average for magnitude and day of peak. Detrended, I got correlation of -0.108
...
I think the negative correlation is what I would expect.

So depending on how the maximum is calculated, you can obtain a weak negative or a weak positive correlation.

Which by extension implies neither correlation, casual relationship, or underlying common cause; at least no simple one.
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BornFromTheVoid

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Re: 2015 sea ice area and extent data
« Reply #59 on: March 01, 2015, 05:47:32 PM »
Update for the week to February 28th

The current 5 day mean is on 14,412,600km2 while the 1 day extent is at 14,354,900km2.
The daily anomaly (compared to 81-10) is at -1,023,690km2, an increase from -979,110km2 last week. The anomaly compared to the 07, 11 and 12 average is at -215,6500km2, an increase from -181,500km2 last week. We're currently 2nd lowest on record, the same as last week.



The average daily change over the last 7 days was +7.7k/day, compared to the long term average of +14.1k/day, and the 07, 11 and 12 average of +12.6k/day.
The average long term change over the next week is +0.4k/day, with the 07, 11, and 12 average being +20.6k/day.




The increase this February was the 9th smallest on record.



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DavidR

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Re: 2015 sea ice area and extent data
« Reply #60 on: March 01, 2015, 09:51:18 PM »
BFTV,
I  can't see any way you  can have the NSIDC extent increasing by a greater amount in 2015 than 2014. My  figures show a maximum increase in Feb of just  414 K in 2015 compared with 470 in 2014.  Measuring from 31 Jan to  28 Feb gives an even starker difference of 230 K vs 456 K. 

Are you using the 5 day  average? That  might explain it as 2015 rose very  rapidly in the last week of January.  OK That's it  417 K in 2014 vs 429 in 2015. 

2015 rose almost 200 K in the last 5 days of Jan compared to  virtually no rise in 2014. The reverse occurred at the end of the month with 2015 dropping 100K and 2014 rising 160.  Hence the variation.
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BornFromTheVoid

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Re: 2015 sea ice area and extent data
« Reply #61 on: March 01, 2015, 10:00:58 PM »
Yup, I'm using the 5 day trailing average, David
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DavidR

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Re: 2015 sea ice area and extent data
« Reply #62 on: March 01, 2015, 10:40:38 PM »
BFTV,
It would be great to  see the entire series for March from now to the maximum to  see how likely  we are to get back up to the record low maximum extent.  On my  figures the average rise from now won't get  us back to the current maximum for 2015.   
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crandles

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Re: 2015 sea ice area and extent data
« Reply #63 on: March 02, 2015, 12:53:48 PM »
For Cryosphere Today area numbers

following path of previous 36 years:

17 fail to get higher than 13.274 reached 11 data days ago
5 rise further but stay below 13.317 so 22 years paths keep this year as 2nd lowest maximum on record
2 rise to between 13.317 and 13.358 to be 3rd lowest maximum on record
4 rise to between 13.358 and 13.460 to be 4th lowest maximum on record
0 rise to between 13.460 and 13.487 to be 5th lowest maximum on record
8 rise to between 13.487 and 13.700 to be 6th lowest maximum on record (current 6th is 13.708)

average increase of last 10 or 36 year puts us 4th lowest maximum on record

If just use last 10 years, 4 show no rise past 13.274 peak. So just under half of the paths whether you use 10 years or 36 years.

BornFromTheVoid

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Re: 2015 sea ice area and extent data
« Reply #64 on: March 02, 2015, 02:09:25 PM »
BFTV,
It would be great to  see the entire series for March from now to the maximum to  see how likely  we are to get back up to the record low maximum extent.  On my  figures the average rise from now won't get  us back to the current maximum for 2015.

Going from the last day of February, the biggest extent increase to the max was 498k, the 95th percentile is 388k, 81-10 average is 136k and several years hit their maximum in February.

With the 5 day average, 11 of the last 36 years would not beat the current max. That doesn't take into account that the 5 day average will probably drop for another few days at least. However given how much extra space we have, especially in the Bering sea and Okhotsk, and how only 1 in the last 10 years didn't hit their max in March, I'd still say there's a ~75% chance that we'll set a new max this month.
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Jim Pettit

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Re: 2015 sea ice area and extent data
« Reply #65 on: March 02, 2015, 02:24:48 PM »
IJIS Extent:
13,827,443 km2 (01 March)
10,649,988 km2 above record minimum extent of 3,177,455 km2 (16 September 2012).
Up 9,126 km2 from previous day.
Down 73,242 km2 over past seven days (daily average: -10,463 km2).
Up 9,126 km2 for the month of March (daily average: 9,126 km2).
820,649 km2 below 2000s average for this date.
362,354 km2 below 2010s average for this date.
219,490 km2 below 2014 value for this date.
700,351 km2 below 2012 value for this date.
Lowest March to-date average.
Lowest value for the date.
6 days this year (10% year-to-date) have recorded the lowest daily extent.
11 days (18.33%) have recorded the second lowest.
17 days (28.33%) have recorded the third lowest.
34 days (56.67%) in total have been among the three lowest on record.


CT Area:
13,087,684 km2 (01 March [Day 0.1616])
10,853,674 km2 above record minimum area of 2,234,010 km2 (14 September 2012).
Up 8,573 km2 from previous day.
Up 61,159 km2 over past seven days (daily average: 8,737 km2).
Up 8,573 km2 for the month of March (daily average: 8,573 km2).
552,195 km2 below 2000s average for this date.
132,852 km2 below 2010s average for this date.
39,822 km2 above 2014 value for this date.
143,094 km2 below 2012 value for this date.
4th lowest March to-date average.
4th lowest value for the date.
0 days this year (0% year-to-date) have recorded the lowest daily area.
1 day (1.67%) has recorded the second lowest.
5 days (8.33%) have recorded the third lowest.
6 days in total (10%) have been among the lowest three on record.


Jim Pettit

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Re: 2015 sea ice area and extent data
« Reply #66 on: March 02, 2015, 02:33:43 PM »
BFTV,
It would be great to  see the entire series for March from now to the maximum to  see how likely  we are to get back up to the record low maximum extent.  On my  figures the average rise from now won't get  us back to the current maximum for 2015.

I maintain a couple of graphics showing just this information. One for IJIS extent:



...and one for CT area:



A quick eyeball shows that, based solely on past years' performances, neither area nor extent may have yet maxed out, though it appears more likely with each passing day...

crandles

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Re: 2015 sea ice area and extent data
« Reply #67 on: March 02, 2015, 04:43:38 PM »
BFTV,
It would be great to  see the entire series for March from now to the maximum to  see how likely  we are to get back up to the record low maximum extent.  On my  figures the average rise from now won't get  us back to the current maximum for 2015.

If you want it in numbers,

16 of last 27 years do not go above prev max this year of 14.539
23 of 27 do not go above record minimum max of 14.671

This is a lot better odds for NSIDC extent numbers having already peaked than for CT area numbers despite their similarity - NSIDC 185k below previous peak this year vs CT area 187k below previous peak this year. You would think that 187k on smaller area numbers would be more significant, but perhaps extra variability means it isn't more significant.

Siffy

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Re: 2015 sea ice area and extent data
« Reply #68 on: March 02, 2015, 04:50:39 PM »
Forgive me if i'm being silly but isn't comparing to how the last x number of years ran from this point on kind of naive or futile? Weather patterns were different in those years in the run up towards their maximums and in that regards using those figures doesn't actually give you a good idea of what's likely to happen later?

I realize I'm probably preaching to the choir here so to speak but as long as the current weather patterns hold isn't it highly probable the maximum has already been reached?

crandles

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Re: 2015 sea ice area and extent data
« Reply #69 on: March 02, 2015, 05:46:48 PM »
Suggesting it will follow year X is a bit silly, it won't follow any year precisely. However if you compare to 36, this may well give a reasonable representation of the range of what is possible. This just assumes that what happens now is pretty much random due to weather.

I have wondered if we could do better though. If you did it from a point where the area/extent had fallen rapidly or risen rapidly in the past few days, it might be sensible to find years where that had also happened and only use those years. i.e. there could well be some autocorrelation rather than just random fluctuations. Either way you end up with probability distribution which cannot be falsified and would take a lot of data to show one such pdf was better than another pdf.


BornFromTheVoid

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Re: 2015 sea ice area and extent data
« Reply #70 on: March 02, 2015, 05:47:33 PM »
Siffy,

Yeah, comparing with another individual year isn't of much use. But to get an idea of the range of likely outcomes, it's ok I think. Weather patterns rarely hold for all that long anyway, and several other years have seen long plateaus and drops into the start of March, so our situation this year isn't entirely unique.

EDIT: Trying a simple way to perhaps improve the method, if you correlate the February extent with each other, then just use all the years that had a value of over 0.9 then you get an average increase of 157k to the maximum, while the top 5 correlated years gives 102k.
« Last Edit: March 02, 2015, 06:07:30 PM by BornFromTheVoid »
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Jim Pettit

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Re: 2015 sea ice area and extent data
« Reply #71 on: March 02, 2015, 06:29:34 PM »
Forgive me if i'm being silly but isn't comparing to how the last x number of years ran from this point on kind of naive or futile? Weather patterns were different in those years in the run up towards their maximums and in that regards using those figures doesn't actually give you a good idea of what's likely to happen later?

I realize I'm probably preaching to the choir here so to speak but as long as the current weather patterns hold isn't it highly probable the maximum has already been reached?

I agree with crandles and BFTV that past performances are not a reliable indicator of future trends, as each year is indeed a different beast. However, as they also both noted, looking back at the entire dataset can give a rough idea of what's likely to occur--or, more to the point, what's not. So, you know, not silly. But YMMV.

viddaloo

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Re: 2015 sea ice area and extent data
« Reply #72 on: March 02, 2015, 06:30:09 PM »
Not that it's very important to 'predict' whether we'll max out later or not, but here's my take (related to IJIS extent):



This is the change in extent for 12 days ahead for 2008—2014. Assuming we're 'safe' if we get to day 13, or March 14th. Red line is 114617 km2, if we gain more, we have a new max extent. After yesterday, only two years — 2010 and 2014 — crossed the line. I'd therefore say there's a 5 in 7 chance that February 15th was the maximum extent this year. 2 in 7 say it comes later.
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DavidR

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Re: 2015 sea ice area and extent data
« Reply #73 on: March 02, 2015, 10:23:41 PM »
For Cryosphere Today area numbers

following path of previous 36 years:

17 fail to get higher than 13.274 reached 11 data days ago
5 rise further but stay below 13.317 so 22 years paths keep this year as 2nd lowest maximum on record
2 rise to between 13.317 and 13.358 to be 3rd lowest maximum on record
4 rise to between 13.358 and 13.460 to be 4th lowest maximum on record
0 rise to between 13.460 and 13.487 to be 5th lowest maximum on record
8 rise to between 13.487 and 13.700 to be 6th lowest maximum on record (current 6th is 13.708)

average increase of last 10 or 36 year puts us 4th lowest maximum on record

If just use last 10 years, 4 show no rise past 13.274 peak. So just under half of the paths whether you use 10 years or 36 years.

These,and other figures quoted here suggest about a 25% chance of a significant rise putting the minimum extent /area  well above the record low. Well at least outside the lowest three.  This probability doesn't seem to have changed over the past 36 years, despite the high rises in area in 3 of the past 5 years.

I've been predicting a low minimum for a while because of the warmth of the Northern Pacific ocean and I  think I'll stick with that  prediction.
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wili

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Re: 2015 sea ice area and extent data
« Reply #74 on: March 03, 2015, 01:39:49 AM »
rs has a new post on this topic: https://robertscribbler.wordpress.com/2015/03/02/arctic-sea-ice-flirts-with-new-record-lows-dragging-global-coverage-inexorably-down/

Arctic Sea Ice Flirts With New Record Lows Dragging Global Coverage Inexorably Down
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

viddaloo

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Re: 2015 sea ice area and extent data
« Reply #75 on: March 03, 2015, 04:21:18 PM »
Yesterday's drop raises the (red) bar somewhat (we now need a bigger gain to beat Feb 15), and it looks like after today, 2010 will be the only year to have such a big gain between now and March 13. With a 7–year sample (not cherry–picked, because it is the 7 latest years, and thus all post–2007 event years, which seems relevant) we will then probably be left with a 1 in 7 chance of reaching a later extent maximum than Feb 15. Barring of course a surprise gain today. Climate Reanalyzer looks very eager to melt Arctic ice for the next week or two, upping the odds of a 2010 gain. I'm thinking century drop before Tuesday 10th.
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deep octopus

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Re: 2015 sea ice area and extent data
« Reply #76 on: March 03, 2015, 04:35:07 PM »
Century rise followed by (almost) century drop on NSIDC extent: 14.36605 millions km2 makes this a daily record low.

viddaloo

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Re: 2015 sea ice area and extent data
« Reply #77 on: March 04, 2015, 05:36:20 AM »


This is the change in extent for 12 days ahead for 2008—2014. Assuming we're 'safe' if we get to day 13, or March 14th. Red line is 114617 km2, if we gain more, we have a new max extent. After yesterday, only two years — 2010 and 2014 — crossed the line. I'd therefore say there's a 5 in 7 chance that February 15th was the maximum extent this year. 2 in 7 say it comes later.
Wow! Just two days later, not only did 2014 dip below the red line, even 2010 did:



In my simplistic estimate model this means 0 of 7 chances of a higher IJIS max than Feb 15.

There are no years post–2007 that sport the amount of refreeze necessary from March 4 to 13, to take us higher than 13.94 million.
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DavidR

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Re: 2015 sea ice area and extent data
« Reply #78 on: March 04, 2015, 08:48:56 AM »
Wow! Just two days later, not only did 2014 dip below the red line, even 2010 did:

In my simplistic estimate model this means 0 of 7 chances of a higher IJIS max than Feb 15.

There are no years post–2007 that sport the amount of refreeze necessary from March 4 to 13, to take us higher than 13.94 million.
NSIDC shows an extent increase after March 13th of 230 K km^2 in 2010. Rapid increases are quite common in March when bad weather hits. So I don't think we can be confident of this years maximum for a couple of weeks yet.

It would be interesting to know if anyone has plotted the distribution of the dates of maximums over all the data sets, and if so if any of the measures show a predominance of early or late maximums. My dataset (post 2007) suggests the CT Area has a tendency to late maximums and more frequent  rapid rises in March. But that's only 8  years.
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Wipneus

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Re: 2015 sea ice area and extent data
« Reply #79 on: March 04, 2015, 08:59:12 AM »
By PM i got the following question:

Quote
: Wipneus  March 01, 2015, 08:00:03
Jaxa AMSR2 data for 20150227 is similar, with Baffin dropping at the same rate as the Bering region. [...] Total Extent -112.4

I'm puzzled by this figure, as the official IJIS numbers do not indicate a century drop here.

What am I missing? Are you excluding lakes or other areas that I am not aware of?

First,  I calculate regional extent and area data from a number of satellite derived sea ice concentration data sets. I do this because:
- regional data is hard to get;
- area data is not provided;
- calculation details differ, e.g. is lake ice included?

Now the question why century yes/no, while they both use Jaxa data. Since in this time of the season concentrating on the largest peak is a study in noise, whether weather related or any uncertainty in the chain of measuring and analysis. Comparing my Jaxa data with the Jaxa/IJIS/IARC extent I can think of the following differences.

- there is no IJIS or IARC in my calculations. I do not know all the what's and the how's of what eaxctly they do;
- For the totals, I only include at this moment the 14 well known regions. Since the IJIS/IARC extent data are consistently well above mine, I guess they include all of the ice. It is not sufficient though, even including all the ice my calculations are still a bit below.
- timing: correlating changes in both measurements show that my calculations lag those of the IJIS/Jaxa numbers. A difference of 12 hours would explain my observations.
- Averaging, they seem to suggest that a 2 day averaging period is used (3 days for the Windsat era). There is no averaging in my calculations;
- the data source:  I am using Level 3 data from Jaxa, that is already processed to some degree. Level 2 data would be an option. I have no idea what the IJIS/IARC calculations use.
- homogenization: IJIS/IARC offer continuous data since 2002 even with different sensors. Some compensation for the differences is likely to make them comparable. Details are unknown.

I publish the data as soon as it is calculated, locations are summarized in this post.

For Jaxa, I use L3 sea ice concentration available here, free registration required.



 

viddaloo

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Re: 2015 sea ice area and extent data
« Reply #80 on: March 04, 2015, 09:01:49 AM »
NSIDC shows an extent increase after March 13th of 230 K km^2 in 2010. Rapid increases are quite common in March when bad weather hits. So I don't think we can be confident of this years maximum for a couple of weeks yet.

DavidR, we're already 2% down or 204K since the max, plus you must remember that 2010 is an extreme outlier year. But even if 2010's refreeze path was to be chosen this year after March 13th, we will be low enough on March 13th to not go above Feb 15 and 13.94.
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DavidR

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Re: 2015 sea ice area and extent data
« Reply #81 on: March 04, 2015, 09:20:15 AM »
DavidR, we're already 2% down or 204K since the max, plus you must remember that 2010 is an extreme outlier year. But even if 2010's refreeze path was to be chosen this year after March 13th, we will be low enough on March 13th to not go above Feb 15 and 13.94.
viddaloo,
in NSIDC records 3 of the past 8 years show extent gains of around 300 K km^2 after March 2nd so I don't think 2010 is that extreme an outlier. It just depends when the icy blast comes, if indeed it  does.

I  have to  say I don't expect it to, and have predicted a near record low maximum for about a month.
http://forum.arctic-sea-ice.net/index.php?action=post;topic=997.msg44884;quote=44884
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viddaloo

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Re: 2015 sea ice area and extent data
« Reply #82 on: March 04, 2015, 09:38:36 AM »
I see. But you'd now have to look at March 4th or after. Every day counts at this time of year, particularly when 2015 has a major drop on March 3rd, and half of that on the 2nd.

My point being: Even 300k as a potential gain before March 13th will hardly be a match for 2015, as we're already this low and at least a week ahead will be extremely mild in the Arctic. We'll go lower than 300k below Feb 15th, therefore the ~11th to 13th gain would have to be gigantic.
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Wipneus

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Re: 2015 sea ice area and extent data
« Reply #83 on: March 04, 2015, 09:54:55 AM »
Next questions:

Quote
with a lot of focus these days on record lows, amid huge differences in the estimates between NSIDC and IJIS, that both claim to measure >= 15% ice concentration, maybe you could just briefly point out why they differ, too? I know I would be curious to read that!


Let me talk about Jaxa instead of IJIS. IJIS and IARC seem to have been removed from all the graphs and website.

- NSIDC is using SMMR, SSM/I and SSMIS instruments on several instruments. Jaxa has used since 2002 the AMSR-E, Windsat and AMSR2 data.;
- NSIDC data is a single data set, explicitly homogenized for climatic purposes. I have serious doubts about Jaxa's homogenization;
- NSIDC uses the "Nasa Team" algorithm. Jaxa the "bootstrap" algorithm;
- NSIDC uses a 25km grid. Jaxa probably used a 12.5 km grid, an since AMSR2 10km;

Most of the differences in extent are probably explained by the last point: extent increases with a courser grid and gives more false ice due to the land spillover effect. The effect on area is much smaller, NSIDC area is mostly below that of Jaxa.

Quote
And if you will: Why should anyone use NSIDC rather than IJIS, or the other way around?

I don't doubt Jaxa ( I am not sure if calling it IJIS is still appropriate) is currently the most accurate available. The uncertainties start to get bigger before 2013. So for comparison with previous years (anything except 2013 and 2014) NSIDC should be used. Especially when searching for records I would add.


BTW I notice now the claim for 15% cut-off is explicitly for AMSR-E. Thus opening the possibility that another threshold is used, I can remember some suggestion that the AMSR2 is accurate enough to lower the limit to 8%. Interesting research subject.

Neven

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Re: 2015 sea ice area and extent data
« Reply #84 on: March 04, 2015, 10:23:55 AM »


Very interesting developments. I wonder two things: What will PIOMAS do with all this, and when will it bounce up again, and by how much? OK, that's three things.
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Re: 2015 sea ice area and extent data
« Reply #85 on: March 04, 2015, 11:41:57 AM »
Very interesting developments. I wonder two things: What will PIOMAS do with all this, and when will it bounce up again, and by how much? OK, that's three things.

I think NSIDC will help to PIOMAS - their vision is slighty different from ijis )

Jim Pettit

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Re: 2015 sea ice area and extent data
« Reply #86 on: March 04, 2015, 01:41:53 PM »
IJIS Extent:
13,738,251 km2 (03 March)
Down 203,809 km2 (1.46%) from 2015 maximum-to-date of 13,942,060 km2 on 15 February.
If extent were to follow the same path from today forward that it did in 2004, 2010, or 2014, we'd see a new 2015 maximum. Only 2010 and 2014 saw enough extent increase from today onward to break the 14 million mark.
10,560,796 km2 above record minimum extent of 3,177,455 km2 (16 September 2012).
Down 59,898 km2 from previous day.
Down 174,601 km2 over past seven days (daily average: -24,943 km2).
Down 80,066 km2 for the month of March (daily average: -26,689 km2).
927,010 km2 below 2000s average for this date.
483,821 km2 below 2010s average for this date.
388,642 km2 below 2014 value for this date.
957,696 km2 below 2012 value for this date.
Lowest March to-date average.
Lowest value for the date.
8 days this year (12.9% year-to-date) have recorded the lowest daily extent.
11 days (17.74%) have recorded the second lowest.
17 days (27.42%) have recorded the third lowest.
36 days (58.06%) in total have been among the three lowest on record.


CT Area:
13,144,496 km2 (03 March [Day 0.1671])
Down 130,059 km2 (0.98%) from 2015 maximum-to-date of 13,274,555 km2 on 17 February [Day 0.1288].
10,910,487 km2 above record minimum area of 2,234,010 km2 (14 September 2012).
Up 7,473 km2 from previous day.
Up 13,650 km2 over past seven days (daily average: 1,950 km2).
Up 65,385 km2 for the month of March (daily average: 21,795 km2).
559,098 km2 below 2000s average for this date.
122,193 km2 below 2010s average for this date.
229,893 km2 above 2014 value for this date.
315,543 km2 below 2012 value for this date.
4th lowest March to-date average.
4th lowest value for the date.
0 days this year (0% year-to-date) have recorded the lowest daily area.
1 day (1.61%) has recorded the second lowest.
5 days (8.06%) have recorded the third lowest.
6 days in total (9.68%) have been among the lowest three on record.


OldLeatherneck

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Re: 2015 sea ice area and extent data
« Reply #87 on: March 04, 2015, 09:19:17 PM »
While I seldom have , or take, the time to comment on this Forum, I'm still avidly following events in the Arctic on a daily basis.  While only a fool would take the current IJIS/JXA Extent to make any prediction about what the final minimum will be in September, it is time to make some reasonable predictions about the 2015 Maximum Extent.

In order for 2015 to not have the lowest IJIS/JAXA Extent on record, it would have to gain another 389,478 Km2.  In my humble opinion, I do not see anyway that will happen in the next 10-15 days.

In order for  the 2015 IJIS/JAXA Maximum Extent to exceed 14M Km2 would require a gain of another 261,749 Km2.. I find this to be highly improbable considering the  state of the ice and the near-term predictions of other commenters.

In order for  the 2015 IJIS/JAXA Maximum Extent to occur later than February 15th, it would have to gain more than 203,809 Km2.  While not impossible to happen this time of year, I  consider this unlikely.

If the 2015 IJIS/JAXA Maximum Extent turns out to be the  13,942,060 Km2, not only will it be the lowest on record, it will be first time below 14M Km2, and the earliest to have ever occurred.  The denialists will have trouble explaining this away, although I trust them to say someting irrelevant or blatantly false.

What does this mean for the remainder of March.  The lowest IJIS/JAXA Extrent ever measured in March was 13,569,042 Km2. on march 30th, 2006.  For 2015 to have a lower Extent than that this month only requires a loss of an additional loss of 169,209 Km2.  Average Extent loss from this date through March 31st for years 2003-2014 was 238,420 Km2.  The only years that did not achieve that were 2010, 2011 (w/gains) and 2012 with a loss of only 165 Km2.  The fact that those were 3 of the  past 5 years may or may not be relevant.....I do not know.


       
            
« Last Edit: March 05, 2015, 02:13:01 AM by OldLeatherneck »
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Buddy

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Re: 2015 sea ice area and extent data
« Reply #88 on: March 04, 2015, 10:47:13 PM »
One thing I would be curious to see....and someone may have already done it.....is to chart the number of days between (a) the date of the winter maximum, and (b) the date of the following minimum.

Over time.....I assume that number has decreased.  And going forward over coming years and decades....I assume that number will SHRINK further.   Certainly the last 15 - 20 years would be fascinating.
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DavidR

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Re: 2015 sea ice area and extent data
« Reply #89 on: March 05, 2015, 02:10:56 AM »
One thing I would be curious to see....and someone may have already done it.....is to chart the number of days between (a) the date of the winter maximum, and (b) the date of the following minimum.

Over time.....I assume that number has decreased.  And going forward over coming years and decades....I assume that number will SHRINK further.   Certainly the last 15 - 20 years would be fascinating.

You  can see the range here.
https://sites.google.com/site/pettitclimategraphs/sea-ice-area#asiammdpdsb
There doesn't appear to be any significant trend, winter and summer aren't really shifting much.

If this years maximum date stays at 17th Feb it  will be the earliest maximum in the record.
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OldLeatherneck

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Re: 2015 sea ice area and extent data
« Reply #90 on: March 05, 2015, 12:10:13 PM »
This almost qualifies for "Shocking News".  I compared the Extent value on March 4th, this year (2015) to March 31st of previous years. Only 2006 had a lower March 31st Extent than March 4th of this year!!

It seems that we are about 4 weeks ahead of schedule.

  Date           Year          EXTENT
March 31st       2006       13,575,600
March 4th   2015    13,688,997
March 31st       2007       13,714,811
March 31st       2005       13,838,113
March 31st       2014       13,877,174
March 31st       2011       13,968,366
March 31st       2013       14,222,135
March 31st       2009       14,234,871
March 31st       2004       14,271,527
March 31st       2008       14,370,732
March 31st       2012       14,530,807
March 31st       2003       14,687,712
March 31st       2010       14,688,540

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Buddy

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Re: 2015 sea ice area and extent data
« Reply #91 on: March 05, 2015, 12:22:05 PM »
That is rather startling.  And the next week will be VERY WARM over a large chunk of the Arctic.  This is really setting up as an "ugly year" for the Arctic.  Amazing what warming oceans can do.

I said 3 years ago that the Arctic would "melt out" except for a few hundred mile strip along the Canadian Archipelago....by September of 2016.....and I have little doubt that will indeed happen.

Too much warming water attacking the ice from all sides......
 
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Jim Pettit

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Re: 2015 sea ice area and extent data
« Reply #92 on: March 05, 2015, 01:35:41 PM »
Keeping in mind that springtime performance is in no way a reliable indicator of the summer minimum, it's still startling to see that, as of today, extent is more than one million square kilometers lower than it was on this same date in 2012. That's nearly the size of California and Texas combined:

04 March 2012: 14,699,717 km2
04 March 2015: 13,688,997 km2

It's important to remember that even 2014 experienced a number of record daily lows in February and March, and that most of the daily record lows for April and May are still held by 2006. 2012--the Arctic sea ice's annus horribilis--didn't move into record territory for good until June, so any predictions made now should be taken with a huge grain of salt.

But, still; a million km2. Yikes...

richie3846

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Re: 2015 sea ice area and extent data
« Reply #93 on: March 05, 2015, 01:46:25 PM »
I've been 'lurking' on this board for a couple years now - this is my first post as I don't normally have much to add to the in-depth scientific knowledge some of the posters have. I suppose you could call me a layman.

Buddy, I am on your side with this one.  I reckon we are looking at virtually ice free over the next 1-2 years. I try not to get bogged down with the details on this board, but take a 'macro' view instead. Some readers of the board may be interested in taking a look at:

http://www.ncdc.noaa.gov/sotc/global/2014/13

What is of particular interest is the fact that the oceans last year were the warmest on record. I know weather conditions can sometimes go against the general trends, but the chances of recording the smallest maximum must surely be greatly amplified by the warm seas. I think we may have 'perfect storm' conditions for ice melt now, because of the warm seas and the possibility of El Nino making an appearance at some point this year. Of course weather conditions could still be favourable for ice retention, but there is a lot of heat already locked away, especially, it seems, in the northern hemisphere.

I wonder if there is any direct correlation between the global annual sea temperature and the minimum/maximum sea ice levels?

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Re: 2015 sea ice area and extent data
« Reply #94 on: March 05, 2015, 02:28:53 PM »
We humans really are pathetic sometimes.  We fail to see the most obvious things that are right in front of our face....if we would just look (and that certainly includes me).

The next few weeks will certainly be interesting.....as we chart the 2015 ice extent.  I expect it to continue to drop....and run parallel, but significantly below the other "low years".  It IS a "future event"....and while none of us know EXACTLY WHEN.....we all know WHERE we are headed.

2015 could very well end up between 1 mill and 2 mill km2.  Do we know that for sure?  Certainly not.  Do we KNOW that as CO2 levels continue to rise, that the temp of the planet continues to rise.....and that the ice sheets will continue to melt.  WE CERTAINLY DO.

The day is coming closer and closer that people that have been lying like Joe Bastardi, Anthony Watts, Sean Hannity, FOX News, and LONG LIST of politicians........are going to have to come up with some answers for their behavior.  The "dark side" of me is going to relish that.



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Re: 2015 sea ice area and extent data
« Reply #95 on: March 05, 2015, 05:03:07 PM »
In terms of the minimum this is the only graph that matters in the short term IMHO. The number of days over 271 Kelvin North of 80 North gives pretty good prediction. Last two years despite high temps in winter short cold high Arctic summer led to increases in ice volume despite fragile state of Arctic. I think we've had a couple of freak years weather wise and if we're above 271 much earlier than day 150 this year it will be interesting. If 2015 is repeat of 2013 & 2014 the possibility of an unknown negative feedback loop becomes stronger.


http://ocean.dmi.dk/arctic/meant80n.uk.php


viddaloo

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Re: 2015 sea ice area and extent data
« Reply #96 on: March 05, 2015, 05:15:04 PM »
If 2015 is repeat of 2013 & 2014 the possibility of an unknown negative feedback loop becomes stronger.

That 'unknown' negative feedback would be increase in wildfires caused by a warming sub–arctic taiga area, again causing more 'fog' or smoke over sea ice, IMnsHO.
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Re: 2015 sea ice area and extent data
« Reply #97 on: March 05, 2015, 05:32:41 PM »
Wouldn't any such smoky shading be a fairly short-term negative but longer-term positive feedback, as soot drops on the ice and changes albedo? (Not to mention the yet-longer-term effect of the GHGs released.)
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viddaloo

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Re: 2015 sea ice area and extent data
« Reply #98 on: March 05, 2015, 05:38:51 PM »
I'm certainly no expert, but I believe soot etc falls out of the sky locally near the fire before wildfire smoke travels thousands of miles to the CAB and stays airborn longer than the larger soot particles? Regarding short–term, you only need to shade the worst insolation period, the 10–15 weeks around Summer Solstice, to have a huge effect. And wildfires burn naturally in that same 'short–term' period, exactly around Solstice. Could very well be a negative feedback, IMO. Question is if it will be sufficient to save us.
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crandles

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Re: 2015 sea ice area and extent data
« Reply #99 on: March 05, 2015, 06:13:18 PM »
NSIDC extent 14.33513 lower than 23 of the last 24 days.

following movements in extent of last 27 years,

21 of last 27 years do not go above prev max this year of 14.539
26 of 27 do not go above record minimum max of 14.671