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Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1650 on: April 29, 2017, 05:06:59 PM »
To make clear, April Volume residuals not saying anything about extent residuals in september, here for 1979-2016

You have plotted April PIOMAS residuals against September NSIDC SIE residuals, but I'm not sure what physical reality this is meant to represent. If I was looking for some correlation between the two data series, I would use a function such as Excel's CORREL.

There are 38 data pairs in the 1979-2016 range. On 11 occasions, each member of the pair is negative, and on 14 occasions, each pair member is positive.

I know this is an artificial example, but try thinking in terms of tossing two coins, and getting either 2 heads{2H}, or 2 tails{2T}. Using the cumulative binomial distribution, the chances of only getting {1H + 1T} on 13 (or less) occasions is less than 1.7%

The fact that there is this degree of agreement demonstrates that there IS a positive correlation, and the p-value derived from the correlation coefficient and the number of Degrees of Freedom subsequently demonstrates the level of statistical significance.

If you consider the direction of the slope on your diagram, you will see that this actually corresponds to a preponderance of the data pairs being either, both negative, or, both positive.

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Re: Latest PIOMAS update (April)
« Reply #1651 on: April 29, 2017, 05:49:47 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.

The correlation is also going down over the last 2 decades.
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Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1652 on: April 29, 2017, 06:19:50 PM »
Just for a giggle, I did a quick correlation analysis between the PIOMAS September residuals and the NSIDC SIE September residuals.

The correlation is also going down over the last 2 decades.

Jai, here are the numbers I get when running CORREL on the PIOMAS September residuals and the NSIDC SIE September residuals...

1979-1998 +0.714
1997-2016 +0.808

I then thought you may have meant that the coefficient might have been dropping in a "jerky" fashion, so I locked the start year as 1979 and incremented the finish year...

1998   +0.714
1999   +0.715
2000   +0.717
2001   +0.741
2002   +0.733
2003   +0.736
2004   +0.738
2005   +0.734
2006   +0.734
2007   +0.751
2008   +0.750
2009   +0.745
2010   +0.735
2011   +0.744
2012   +0.773
2013   +0.755
2014   +0.760
2015   +0.758
2016   +0.755


Of course, as as been demonstrated before, it's not unheard of for me to pair up the wrong two columns.

I'll check my homework  ;)



Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1653 on: April 29, 2017, 07:07:53 PM »
Bill,

R= sqrt(R^2), so R^2 = 0.11 tells you that the linear relationship between the residuals of Volume in April to  Extent-Residuals in September is very weak. For Example, in June R^2 becomes arround 0.5, that its because June puts on the Melt-Moment, if June melt is weak, its like a cascade effect (also for late snow falls). So therefor, April-Volume is weak linear correlates, because a strong negative residual volume anomaly in april could cause only a weak negative residual anomaly in setember extent, if summer only have a weak melt saison.

So there is no really predicative forecast skill with april volume. In my own Model i use Temperature(T2m) and SST in June/July over a specific domain and forecast Extent-Residuals in Sepember with only 0.36 Mio km^2 Sigma1-Error

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Re: Latest PIOMAS update (April)
« Reply #1654 on: April 29, 2017, 08:25:52 PM »
Bill,

I meant r^2 values for Sept. monthly avg values

For
r^2 NSIDC SIE SEPT. monthly avg. vs. PIOMAS SEPT. monthly avg 
1979-2016 =  0.895
1996-2016 =  0.871
2005-2016 =  0.546

This shows that as total volume is thinning post 2005 that the increase in fracture, ice mobility and the bias of extent analysis to overestimate coverage (i.e. brash ice) is invalidating SIE as the primary sept. minimum ice metric.   (it is not correlating)
« Last Edit: April 29, 2017, 08:41:21 PM by jai mitchell »
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Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1655 on: April 29, 2017, 08:48:56 PM »
jay

Dosent seem fair, you have to make analysis on a constant time scale, so therefor its seem more fair to use a constant time scale (here i use 10y) and make a running r-correlation (Sept Extent:Volume September)



dosibl

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Re: Latest PIOMAS update (April)
« Reply #1656 on: April 29, 2017, 08:57:28 PM »
This seems a bit out of scope for a discussion of current PIOMAS numbers, might be better suited in a new thread?

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1657 on: April 30, 2017, 12:54:25 AM »
I agree with the comment from dosibl that this is getting into a statistics discussion, rather than a PIOMAS discussion.

However, if I am making a mistake in the way I try to use the available statistical functions, then I would be more than happy to be educated in their correct use. (Although that is always a difficult task where I'm concerned   :o) .

Therefore, can I just ask why R_W and Jai are NOT using a function such as CORREL?

I am pretty familiar with using the Coefficient of Determination (ie the R2 value) when one plots a traditional dependent variable versus independent variable chart, such as the decline of the September SIE through time, or the rise in global temperature anomaly through time.

When one then adds a trend line, the resultant R2 gives a measure of the unexplained variance. My understanding (again, this is always questionable) is that the fraction of the variance left unexplained is generally treated as being equal to { 1 - R2 }

I don't understand (and, yet again, that could be all down to my lack of in-depth knowledge) why you are choosing to use this metric when plotting two sets of residuals, instead of using a function such as CORREL - especially when it seems that CORREL has been specifically designed to calculate the correlation coefficient between two data series.

http://www.excel-easy.com/examples/correlation.html

https://support.office.com/en-us/article/CORREL-function-995dcef7-0c0a-4bed-a3fb-239d7b68ca92?ui=en-US&rs=en-US&ad=US&fromAR=1


Perhaps we can iron this out using the forum's Messages functionality, rather than clogging the thread?

jai mitchell

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Re: Latest PIOMAS update (April)
« Reply #1658 on: April 30, 2017, 05:43:52 AM »
correlation between SIE and PIOMAS post 2005 are deviating from the norm.  R_W's post shows decadal averages and equates later decade's loss deviation with the deviation that was found with maximum >4 year ice in the early satellite period.  My point is that post 2005 the correlation value declines significantly between PIOMAS and SIE values.  This indicates that many studies that rely on SIE alone, (correlated to GMST and CO2 cumulative emissions) are understating the reality of actual ice conditions during the September minimum. 

Using CORREL or excel to derive r^2 values does not matter.  The values are the same.  and yes, if we are to continue this discussion we should transfer to a new thread.
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Re: Latest PIOMAS update (April)
« Reply #1659 on: April 30, 2017, 08:35:14 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.}

Thank you Bill. Much appreciated.
First thing I noticed is that you and Random_Weather agree.
Your correlation between PIOMAS April numbers and NSIDC September numbers is R=0.342, which gives R^2=0.117 which is exactly what Random_Weather reported (thank you for that scatter plot RW!).

And both of you are right that this is not a strong correlation (explains only 11.7% of the variability).

So PIOMAS in April is not a good predictor of September SIE.

And to get back on track for this thread, that conclusion actually gives me some hope, :

After all, with PIOMAS numbers running so low right now, I am concerned about volume left over after even an average melting season. But since the correlation is so low, we may see a 'realignment' of PIOMAS numbers before this melting season is over...
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Rob Dekker

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Re: Latest PIOMAS update (April)
« Reply #1660 on: April 30, 2017, 08:46:18 AM »
That said, I still cannot think of any 'physical' property that would reduce the 'volume' of melt if April ice is thin.
So I'm still concerned, and surprised by the poor correlation between ice volume in April and September SIE.

There has to be a way to measure the influence of a warm winter, with resulting low ice volume in April, on the sea ice extent left over in September.
Anything that is better than the linear trend (which gives us a pretty tight 550 k km^2 Standard Deviation).

Maybe we are overlooking something.
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Re: Latest PIOMAS update (April)
« Reply #1661 on: April 30, 2017, 03:10:22 PM »
That said, I still cannot think of any 'physical' property that would reduce the 'volume' of melt if April ice is thin.
So I'm still concerned, and surprised by the poor correlation between ice volume in April and September SIE.

There has to be a way to measure the influence of a warm winter, with resulting low ice volume in April, on the sea ice extent left over in September.
Anything that is better than the linear trend (which gives us a pretty tight 550 k km^2 Standard Deviation).

Maybe we are overlooking something.
I am sure I asked the qu on correlation between max and min  VOLUMES and the answer was 0.65 . And not a correlation twixt vol and SIE. Apologies for not remembering who did it - Steven on this thread ?

So is the question as to why such a poor link twixt SIE and vol ?
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Re: Latest PIOMAS update (April)
« Reply #1662 on: April 30, 2017, 04:22:28 PM »

So I'm still concerned, and surprised by the poor correlation between ice volume in April and September SIE.



Hi Rob,

Thats because of variance in melt intensity in summer, in other words, if melt saison is weak it partly or complete compensate the lower april volume. Ok, i think that trivial, so lets go to the base, a weak or strong melt saison is formed mainly due atmosphere conditions aka early melt ponds... so the thing is, april atmosphere condition also tells nothing about summer atmosphere conditions.

So in the End, so long as volume in april is higher then the weakest possible summer melt, so long will april volume produce different extent outcomes in september, because in april its not clear if there is coming a strong or weak melt sasion.

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Re: Latest PIOMAS update (April)
« Reply #1663 on: April 30, 2017, 04:38:32 PM »
@ Rob again,

Quote
There has to be a way to measure the influence of a warm winter, with resulting low ice volume in April, on the sea ice extent left over in September.

It does, but its not on a year to year base, as said before, its not possible for confident forecast summer melt saison. If you would take 5y Extent and 5y April Volume, i think (not testet yet) the residual correlation would become much stronger, because a 5y mean would cancel some weather effects on melt saison out and the reduction of volume becomes more important

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Re: Latest PIOMAS update (April)
« Reply #1664 on: April 30, 2017, 06:20:54 PM »
I would suggest that there is a very strong correlation between april volume max and september volume minimums.  the deviation in the post-2005 period between volume and extent metrics shows that, as thicker multi-year ice has been lost, the dynamics of arctic melt are changing.  This is also born out from the average thickness graph per year which is changing dramatically.  The inability to capture the changing nature of what sea ice extent is telling us, by assuming that what it says today compared to what it said in 1996 is a flawed use of the metric. 

It should be expected that as older, thicker ice volume is lost over the melt years that the behaivour of the melt will change.  It also stands to reason that Sea Ice Extent will show an inflated value over this period as ice disperses and is counted as coverage though it is only centimeters thick.  This is why i declare that sea ice extent is an anachronistic measure and its use as the primary method to communicate ice conditions in the September minimum is no longer appropriate.

It should be expected that sea ice extent will continue to lag behind volume until some critical threshold of volume is reached and then SIE will collapse quite suddenly (I expect this to occur sometime around 750 km^3).

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Random_Weather

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Re: Latest PIOMAS update (April)
« Reply #1665 on: April 30, 2017, 06:46:30 PM »
Quote
I would suggest that there is a very strong correlation between april volume max and september volume minimums.

hmm more good, not a very strong,for April Residuals Volume and Residuals September Volume in 1979-2016



Quote
It should be expected that sea ice extent will continue to lag behind volume until some critical threshold of volume is reached and then SIE will collapse quite suddenly (I expect this to occur sometime around 750 km^3).

I would expect that variance between minimum to minimum will increase, because the less thicker ice will make the ice stronger respond to weather pattern, on the other hand, distribution of ice thickness is also important, is thick ice concentrated on a small area or a wide area, if its on small it could survive the melt saison although the full volume would suggest it could melt all of it
« Last Edit: April 30, 2017, 06:55:53 PM by Random_Weather »

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Re: Latest PIOMAS update (April)
« Reply #1666 on: April 30, 2017, 07:28:23 PM »
It should be expected that sea ice extent will continue to lag behind volume until some critical threshold of volume is reached and then SIE will collapse quite suddenly (I expect this to occur sometime around 750 km^3).

Can you explain your rationale behind the 750 km^3 figure?   I fully expect the regime to change when there is no longer enough ice to keep the ocean cold, but I have not so far found a good metric for when this will happen.

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Re: Latest PIOMAS update (April)
« Reply #1667 on: April 30, 2017, 08:11:17 PM »
this is the correlation I am speaking of, as opposed to, you know, sea ice extent
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Re: Latest PIOMAS update (April)
« Reply #1668 on: April 30, 2017, 08:18:30 PM »
And tells nothing, because both are autocorrelated or in other word, what makes them good in correlation is only their trend, but it say nothing about the real correlation

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Re: Latest PIOMAS update (April)
« Reply #1669 on: April 30, 2017, 08:23:35 PM »

It should be expected that as older, thicker ice volume is lost over the melt years that the behaivour of the melt will change.  It also stands to reason that Sea Ice Extent will show an inflated value over this period as ice disperses and is counted as coverage though it is only centimeters thick.  This is why i declare that sea ice extent is an anachronistic measure and its use as the primary method to communicate ice conditions in the September minimum is no longer appropriate.

It should be expected that sea ice extent will continue to lag behind volume until some critical threshold of volume is reached and then SIE will collapse quite suddenly (I expect this to occur sometime around 750 km^3).

And this is exactly how the ice is behaving in an Arctic with far less MYI and a declining volume at max which is comprised of far more FYI. The dispersion of ice at minimum has been increasing for almost 4 decades and there have been dramatic steps up in dispersion following years where MYI and volume took hits in high melt years.

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Re: Latest PIOMAS update (April)
« Reply #1670 on: April 30, 2017, 08:55:54 PM »
Just because residuals to the linear fit do not have a strong r^2 does not mean that there is a better/different model (than the linear fit with high direct r^2).  Find me a better fit curve with (significantly) higher residual coefficients.
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Re: Latest PIOMAS update (April)
« Reply #1671 on: April 30, 2017, 09:16:19 PM »
Jai,

Have already done, a Model based on June Data R^2 becomes 0.44 for residuals in SIE in September, Model based on JJA becomes R^2= 0.68

Here residuals of Observation (SIE in September) and Model (JJA)


Good enough?

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Re: Latest PIOMAS update (April)
« Reply #1672 on: April 30, 2017, 09:18:37 PM »
PS: As said before, all things are nearly useless before summer comes, the summer makes the things up

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Re: Latest PIOMAS update (April)
« Reply #1673 on: April 30, 2017, 09:29:54 PM »
Good enough?

Yes, that is great!  JJA is a great predictor for Sept Min. (better than April)
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oren

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Re: Latest PIOMAS update (April)
« Reply #1674 on: April 30, 2017, 10:55:22 PM »
Gents, this should have been in a new thread since many posts ago, both for the sake of readers looking for PIOMAS updates and related info, and for the sake of those who want to dive deep an make long term calculations and statistics and revisit the correlations in a few months or even years.

Rob Dekker

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Re: Latest PIOMAS update (April)
« Reply #1675 on: May 01, 2017, 07:37:34 AM »
This discussion might not fit the exact definition of "Latest PIOMAS update", but since the latest PIOMAS update reported record low numbers, it is not out-of-thread to discuss what these record low numbers mean for the upcoming minimum.

Also, anyone looking for exact PIOMAS updates ONLY (and not the implications of them for September SIE) can also follow Neven's monthly updates on the ASIB.

I don't think a bit of statistics is hurting this thread.
In fact, it makes it more interesting IMHO.
« Last Edit: May 01, 2017, 07:48:23 AM by Rob Dekker »
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Re: Latest PIOMAS update (April)
« Reply #1676 on: May 01, 2017, 08:10:41 AM »
Have already done, a Model based on June Data R^2 becomes 0.44 for residuals in SIE in September, Model based on JJA becomes R^2= 0.68

RW, thanks !
Do you have a similar graph (as you did for JJA) for June PIOMAS volume (regressed against September SIE) ? And what you find as the SD for the residuals of that (June) model ?
That would tell something about the predictive value of (June) PIOMAS volume numbers.
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Re: Latest PIOMAS update (April)
« Reply #1677 on: May 01, 2017, 08:15:51 AM »
Quote
I don't think a bit of statistics is hurting this thread.
In fact, it makes it more interesting IMHO.

No objections at all, if needed I can change the topic name (but I hate long subjects).

Not that this discussion has not been held before. The conclusion is similar: best predictor of September volume minimum is last years (capturing the long trend) minimum combined with June (or later) volume of the current year.

It is not a very linear system though, so every number that assumes it is should be regarded with caution.

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Re: Latest PIOMAS update (April)
« Reply #1678 on: May 01, 2017, 09:39:20 AM »


RW, thanks !
Do you have a similar graph (as you did for JJA) for June PIOMAS volume (regressed against September SIE) ? And what you find as the SD for the residuals of that (June) model ?
That would tell something about the predictive value of (June) PIOMAS volume numbers.

Hi,

No, to make its clear, its not volume, its T2m and SST on a arctic domain which is put together to a model which is very good after May. It dont need Volume, because its respresent volume in a indirect way also for summer melt conditions. So as you ask here some skills of Model (to predict SIE September)


Month : Sigma1

June = 0.41 Mio km^2
July = 0.40 Mio km^2
August = 0.38 Mio km^2

For Summer-Saison
JJA  = 0.32 Mio km^2


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Re: Latest PIOMAS update (April)
« Reply #1679 on: May 01, 2017, 03:09:16 PM »
Have already done, a Model based on June Data R^2 becomes 0.44 for residuals in SIE in September, Model based on JJA becomes R^2= 0.68

RW, thanks !
Do you have a similar graph (as you did for JJA) for June PIOMAS volume (regressed against September SIE) ? And what you find as the SD for the residuals of that (June) model ?
That would tell something about the predictive value of (June) PIOMAS volume numbers.

The correlation between detrended June PIOMAS volume and detrended September sea ice extent is R = 0.605.  Since the standard deviation of detrended September sea ice extent is 0.55 million km2,  the standard deviation of the residuals from the regression is then equal to  SQRT(1 - R2) * 0.55 = 0.437 million km2.

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Re: Latest PIOMAS update (April)
« Reply #1680 on: May 02, 2017, 07:14:47 AM »
RW, Steven, thanks guys !
Looks like RW's model or June PIOMAS numbers are a decent (but not great) predictor of September SIE.

I also think that Wipneus has a point about incorporating prior year's minimum volume.
After all, the strength of winter freezing is best included by subtracting prior-year's minimum ice volume.
Or maybe we could go all-out and estimate FYI thickness as :
(Volume_now - Volume_prior_year_min) / (Area_now - Area_prior_year_min).
And see what if that serves as a better predictor.

Incidentally, Steven, that  SQRT(1 - R^2) factor only works if you are calculating the SD for 'detrended' variables, right ?
« Last Edit: May 02, 2017, 07:24:47 AM by Rob Dekker »
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Re: Latest PIOMAS update (April)
« Reply #1681 on: May 02, 2017, 07:45:29 AM »
Incidentally, RW, do you have a post somewhere where you explain your model ?
Or did you make an entry for Arcus SIPN where we can read about it ?
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Re: Latest PIOMAS update (May)
« Reply #1682 on: May 02, 2017, 09:22:50 AM »
There was a late-april update of the so called giceday data. Giceday is a gridded piomas data that specifies the thickness distribution in each gridcell, using dividing the ice into 12 thickness categories.

From giceday I can calculate average thickness from which volume is calculated. This does not exactly reproduce the official volume data but it is close enough.

With that said, volume on day 115, 25th April is about 20.7 [1000 km3]. If confirmed, that means the "volume gap" does not seen to be closing. More likely the opposite.

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Re: Latest PIOMAS update (April)
« Reply #1683 on: May 02, 2017, 09:30:00 AM »
Incidentally, RW, do you have a post somewhere where you explain your model ?
Or did you make an entry for Arcus SIPN where we can read about it ?

Rob, yes, if arcus is calling for june report, then my model will start and explained on there webside. This should happen arround the End of May. Before, i dont want to share exactly what i did.

slow wing

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Re: Latest PIOMAS update (May)
« Reply #1684 on: May 02, 2017, 11:38:00 AM »
Thanks Wipneus! So was 25 April the date of maximum sea ice volume by that method?

oren

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Re: Latest PIOMAS update (May)
« Reply #1685 on: May 02, 2017, 11:39:26 AM »
Thanks Wipneus. The most awaited number is in, even if an estimate.
A growth of ~1.07 is similar to almost all years with Mar vol <23, except 2016 which grew less.
Theoretically low Mar thickness and volume coupled with reasonable temps this month could have brought higher growth, but that did not happen and we are still on track for what could easily become a record low volume year.

Bill Fothergill

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Re: Latest PIOMAS update (April)
« Reply #1686 on: May 02, 2017, 12:28:33 PM »
...
Thank you Bill. Much appreciated.
First thing I noticed is that you and Random_Weather agree.
Your correlation between PIOMAS April numbers and NSIDC September numbers is R=0.342, which gives R^2=0.117 which is exactly what Random_Weather reported (thank you for that scatter plot RW!).
...
So PIOMAS in April is not a good predictor of September SIE
...

I've said it before, and will doubtless say it again.. D'Oh!!!!  :-[

Sorry for being so slow guys.

Can I just point out that I never said April PIOMAS figures had great skill at predicting the September SIE. The question originally was along the lines of did early month PIOMAS have more skill than early month SIE.

As Rob and I both wrote articles on the ASIB a few years ago discussing how weak (i.e non-existent) the April:September SIE relationship was, the bar was set pretty low to start with.

However, I still think that the April PIOMAS: September SIE correlation can correctly be described as "significant, but weak". Given such a tenuous relationship, it would never occur to me to do a September prediction predicated solely upon a single variable - and certainly not one involving SIE.

Wipneus

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Re: Latest PIOMAS update (May)
« Reply #1687 on: May 02, 2017, 01:01:04 PM »
Thanks Wipneus! So was 25 April the date of maximum sea ice volume by that method?

Volume was rather flat, in the last 12 days all daily numbers rounded to 20.7.
Here is the tail, April 11-25, rounded to 2 figures:

20.61, 
20.62, 
20.65 , 
20.66 ,
20.69, 
20.73, 
20.73, 
20.73,
20.72 , 
20.72, 
20.72, 
20.71,
20.71, 
20.72, 
20.72

Neven

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Re: Latest PIOMAS update (May)
« Reply #1688 on: May 02, 2017, 01:04:50 PM »
With that said, volume on day 115, 25th April is about 20.7 [1000 km3]. If confirmed, that means the "volume gap" does not seen to be closing. More likely the opposite.

That's interesting, and also somewhat surprising, as I expected this month to show a big uptick (given low volume and low temps).

But you're right. At April 25th the max has probably passed already, so end of month should be even lower (average loss for the last 10 years between April 25th and 30th is around 170 km3, but it could also be no more than 44 km3 (2014) or 51 km3 (2007)).

I eagerly await the numbers...
Compare, compare, compare

Random_Weather

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Re: Latest PIOMAS update (May)
« Reply #1689 on: May 02, 2017, 01:26:57 PM »

That's interesting, and also somewhat surprising, as I expected this month to show a big uptick (given low volume and low temps).


Hi Neven,

I think its because of the high temperature anomalies arround pacific side and the transport of ice to the atlantic where its fighting against the warm north atlantic current also transport due framstrait.

And temperature never was so low, just 0.2K less warm then 2016
http://www.karstenhaustein.com/reanalysis/gfs0p5/ANOM2m_monthly/ANOM2m_GFS_monthly_arctic.php?date=Apr%A02016&file=ANOM2m_CFSR_GFS_1604_monthly_arctic.png
http://www.karstenhaustein.com/reanalysis/gfs0p5/ANOM2m_monthly/ANOM2m_GFS_monthly_arctic.php?date=Apr%A02017&file=ANOM2m_CFSR_GFS_1704_monthly_arctic.png

gerontocrat

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Re: Latest PIOMAS update (May)
« Reply #1690 on: May 02, 2017, 03:35:01 PM »
Below is the jaxa amrs2 volume graph.

It shows a 2,000 km3 fast increase from late March to early April. For the rest of the month it wobbles around at just below 22,000 km3. i.e. although a larger figure, it does mirror a hiatus in volume growth for the latter half of April.

"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

Yuha

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Re: Latest PIOMAS update (May)
« Reply #1691 on: May 02, 2017, 06:28:32 PM »
Volume was rather flat, in the last 12 days all daily numbers rounded to 20.7.
Here is the tail, April 11-25, rounded to 2 figures:

So the April average is about 20.65. That is obviously a new record low for April, by a big margin, but it is also significantly lower than the May average has ever been (20.993 in 2016 is the lowest).

seaicesailor

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Re: Latest PIOMAS update (May)
« Reply #1692 on: May 02, 2017, 07:59:00 PM »

That's interesting, and also somewhat surprising, as I expected this month to show a big uptick (given low volume and low temps).


Hi Neven,

I think its because of the high temperature anomalies arround pacific side and the transport of ice to the atlantic where its fighting against the warm north atlantic current also transport due framstrait.

And temperature never was so low, just 0.2K less warm then 2016
http://www.karstenhaustein.com/reanalysis/gfs0p5/ANOM2m_monthly/ANOM2m_GFS_monthly_arctic.php?date=Apr%A02016&file=ANOM2m_CFSR_GFS_1604_monthly_arctic.png
http://www.karstenhaustein.com/reanalysis/gfs0p5/ANOM2m_monthly/ANOM2m_GFS_monthly_arctic.php?date=Apr%A02017&file=ANOM2m_CFSR_GFS_1704_monthly_arctic.png
Exactly. Although the Bering and Oshkosh have vanished they dont count as much as the gradually melting MYI that has been transported to Greenland sea since March... and the "piling up" of MYI against Svalbard, where melting at great rate must be happening as we speak. If the model picks that.

VeliAlbertKallio

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Re: Latest PIOMAS update (May)
« Reply #1693 on: May 02, 2017, 11:05:11 PM »
jaxa amrs2 volume graph 2016 v. 2017:

Being an old style weather 'chartist' in forecasting future based on old patterns in weather maps, the graph comparison suggests me that 2017 will follow 2016. Last year had also been following the lowest sea ice volume for months until April. By April the lowest lines had converged, but then in 2016 the red line continues soon again to trail beneath all others.

If things were to happen the last year way and mimic it, we should now see May and two weeks in June trailing the lowest again. But then, last year the sea ice melting stalled for the summer to re-emerge at the end of August 2016 and run lowest until the end of this April (2017) when the three lowest lines again converged. The pulverisation, however, this winter is strongest and I fear the leads will trap heat enough and so keep the melt going this time further into summer.

Below is the jaxa amrs2 volume graph.

It shows a 2,000 km3 fast increase from late March to early April. For the rest of the month it wobbles around at just below 22,000 km3. i.e. although a larger figure, it does mirror a hiatus in volume growth for the latter half of April.

oren

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Re: Latest PIOMAS update (May)
« Reply #1694 on: May 02, 2017, 11:06:28 PM »
With that said, volume on day 115, 25th April is about 20.7 [1000 km3]. If confirmed, that means the "volume gap" does not seen to be closing. More likely the opposite.

That's interesting, and also somewhat surprising, as I expected this month to show a big uptick (given low volume and low temps).

But you're right. At April 25th the max has probably passed already, so end of month should be even lower (average loss for the last 10 years between April 25th and 30th is around 170 km3, but it could also be no more than 44 km3 (2014) or 51 km3 (2007)).

I eagerly await the numbers...
Another tiny piece of detail, the growth from End-March to Apr 25th was ~0.32 km3, more or less the average of the last few years. The negative feedback of low volume leading to higher growth failed to materialize.

CognitiveBias

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Re: Latest PIOMAS update (May)
« Reply #1695 on: May 03, 2017, 12:48:14 PM »
Another tiny piece of detail, the growth from End-March to Apr 25th was ~0.32 km3, more or less the average of the last few years. The negative feedback of low volume leading to higher growth failed to materialize.

Yes, according to the model.  The physical reality 'feels' like it should yield a higher growth.  Any ideas on what would drive PIOMAS lower than expected?

Tigertown

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Re: Latest PIOMAS update (May)
« Reply #1696 on: May 03, 2017, 04:23:25 PM »
Another tiny piece of detail, the growth from End-March to Apr 25th was ~0.32 km3, more or less the average of the last few years. The negative feedback of low volume leading to higher growth failed to materialize.

Yes, according to the model.  The physical reality 'feels' like it should yield a higher growth.  Any ideas on what would drive PIOMAS lower than expected?
One guess: Failure of lwr to efficiently escape to space, even from open water. The heat has been replenished at a greater rate than it could escape, even in the heart of winter.

Jim Williams

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Re: Latest PIOMAS update (May)
« Reply #1697 on: May 03, 2017, 05:01:00 PM »
Another tiny piece of detail, the growth from End-March to Apr 25th was ~0.32 km3, more or less the average of the last few years. The negative feedback of low volume leading to higher growth failed to materialize.

Yes, according to the model.  The physical reality 'feels' like it should yield a higher growth.  Any ideas on what would drive PIOMAS lower than expected?

The Atlantic Ocean.

CognitiveBias

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Re: Latest PIOMAS update (May)
« Reply #1698 on: May 03, 2017, 05:09:59 PM »
Wouldn't it have to be something PIOMAS could capture?

FishOutofWater

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Re: Latest PIOMAS update (May)
« Reply #1699 on: May 03, 2017, 05:38:25 PM »
Warm, relatively humid air has continued to be advected from both the Pacific and Atlantic oceans over the Arctic seas. Conditions were very poor for ice growth in the Arctic seas extending from Alaska to Eurasia, because of the warm air advection. Moreover, winds were favorable for transport of the thickest ice in the Arctic towards and out of the Fram strait. All in all the weather in April was not favorable for much ice growth.