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Author Topic: Latest PIOMAS update (June)  (Read 452002 times)

Wipneus

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Re: Latest PIOMAS update (June)
« Reply #50 on: June 10, 2013, 09:16:05 PM »
Wipneus,

Is that TOA or surface, adjusted for angle of incidence?

Yet an answer: atmosphere is ignored and the angle of incidence is taken into account.

ChrisReynolds

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Re: Latest PIOMAS update (June)
« Reply #51 on: June 10, 2013, 09:59:20 PM »
I've just been doing some trigonometry and it's really obvious: Insolation must be highest at the pole since as one moves south from the pole the angle of incidence begins to vary substantially.

Wipneus

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Re: Latest PIOMAS update (June)
« Reply #52 on: June 11, 2013, 07:43:01 AM »
insolation vs latitude was discussed on the asi blog here:

http://neven1.typepad.com/blog/2011/10/september-2011-sea-ice-extent-looking-ahead.html

Wipneus

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Re: Latest PIOMAS update (July)
« Reply #53 on: July 04, 2013, 11:30:51 AM »
Updated, graphs in the top post.

crandles

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Re: Latest PIOMAS update (July)
« Reply #54 on: July 04, 2013, 01:03:12 PM »
Great work and fast as always.

At 31 May (day 151) we had 0.9 K Km^3 more than last year (19.087 vs 18.186)

By 23 Jun (Day 174) the gap had doubled to 1.861 K Km^3 (14.662 vs 12801)

In last 7 days, volume has begun to catch up a little and gap is down to 1.72 K Km^3 (13.002 vs 11.282).

At that rate of catch up, it would take more than 12 weeks to catch up, and we haven't got that long.

I also doubt that that rate of catch up would continue once Hudson, Baffin, and South Western Kara melt out. i.e. we may be catching up because we are melting over a larger area. The areas will become more similar as current thin low latitude ice areas melt and then what would be the reason for melting more volume to continue catching up? This year has had more ice area therefore less ocean collecting heat so there may well be less volume melt again later in the season.

wanderer

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Re: Latest PIOMAS update (July)
« Reply #55 on: July 04, 2013, 01:10:07 PM »
As expected, but now confirmed!
This melt season is so exciting - I wonder how the last days of fast melting show up in next month's graph!

Wipneus

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Re: Latest PIOMAS update (July)
« Reply #56 on: July 04, 2013, 01:23:29 PM »
For what I thought I knew about the ASI, this is a both sobering and exciting season.

Anyway, the anomaly is now at minimum (normally ) and at a level slightly above 2010. We are going to the part of the season where the negative swing of the anomaly will get smaller again.

One of the proposed reasons for this was that the easy ice was gone, that reason is not valid now. If the anomaly stays constant, or even get lower than anything is still possible.

Richard Rathbone

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Re: Latest PIOMAS update (July)
« Reply #57 on: July 04, 2013, 01:42:18 PM »
Catch up with May, though not April, is to be expected. There's some sort of mechanism that means fast melt in June makes it harder to melt in July through September. and vice versa, because that's the way the historical data tend to go. May 31 to minimum is surprisingly close to a constant loss. You aren't backing off that finding of yours are you crandles? I reckon its pretty solid. I'd guess the mechanism as a mixture of thickness distribution and insolation peak sharpness.

Its not quite as far off June 2012 as I was thinking it would be, so I'll push my expectation of this year's minimum volume down a little, and say it comes in at 0.5M above 2012. I still reckon catchup with 2012 and a new record by a narrow margin is possible, but it would take the right weather all the way.

The next region in line for contributing to catch up is Beaufort.

Vergent

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Re: Latest PIOMAS update (July)
« Reply #58 on: July 04, 2013, 02:47:35 PM »
Arctic ice volume is kilo scale km^3, not mega scale. Sorry for the nit picking, but being off by a factor of 1,000..... Its like squeaking the chalk on the blackboard.

Vergent
« Last Edit: July 04, 2013, 02:55:31 PM by Vergent »

Richard Rathbone

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Re: Latest PIOMAS update (July)
« Reply #59 on: July 04, 2013, 04:49:48 PM »
T not kk3 if you are being picky in SI (no stacking allowed). ;)

M for thousand and MM for million if you stack prefixes American style.

If usage is loose it could be a thousand or a million of anything and if the magnitude isn't clear from the context you should always ask the user to clarify rather than assume they are using it the same way you are. M on its own is seriously ambiguous when used across cultures.

Jim Pettit

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Re: Latest PIOMAS update (July)
« Reply #60 on: July 04, 2013, 05:24:36 PM »
The year with the lowest volume lost after June 30 was--drum roll, please--2012. That's because so much of the fringe ice was gone by July 1 last year, which is obviously not the case this year. In fact, as this chart shows, post-June volume loss has been decreasing over the years as more and more ice has been melting earlier and earlier:



So my observations/assumptions/thoughts are these:

1) Roughly the same amount of volume is lost every year (between 16.5k and 17k km3);

2) This year's currently higher volume isn't due to thicker ice in the middle of the pack, but later-melting ice at the fringes;

3) That ice at the fringes is going to melt anyway, as it does nearly every year;

4) Extent and area have both indicated over the past several days that insolation is finally catching up, and they're starting to drop in earnest;

5) 2013 had the lowest volume maximum on record.

Upshot: there's a better than 50% chance that this year's mid-September volume minimum will be a new record. (I put it at 3.15k km3).

Frivolousz21

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Re: Latest PIOMAS update (July)
« Reply #61 on: July 04, 2013, 05:37:53 PM »
How much of this is peripheral ice that didn't melt out vs 2010, 2011, and 2012?


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crandles

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Re: Latest PIOMAS update (July)
« Reply #62 on: July 04, 2013, 07:04:20 PM »

3) That ice at the fringes is going to melt anyway, as it does nearly every year;

4) Extent and area have both indicated over the past several days that insolation is finally catching up, and they're starting to drop in earnest;


Average thickness for last three years (PIOMAS vol/CT Area)
1.747857842
1.70610248
1.71219451

If the average thickness was particularly low because of large areas of very thin ice at low latitude then you might have a point.

As it is, in a couple of weeks the area will have caught up some but this will mean that the average thickness will be noticeably higher than last year as well as still having more area.

So I don't think your argument works.

Dromicosuchus

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Re: Latest PIOMAS update (July)
« Reply #63 on: July 04, 2013, 07:20:42 PM »
Oh, thank goodness.  I have to say I wasn't expecting this, as I supposed that Ekman pumping acting on the fractured ice near the center would have drawn volume down.  I suppose the long-lasting perimeter saved the day.  I'm interested by the similarity between this year's June average uptick and that that occurred in 2008; it begins to look, to me at least, like this will end up being another "recovery" year (I know, I know, it's hardly a recovery and the trend continues.  A hiatus year?), which I have to say is welcome.  Time is precious, and the longer the Arctic holds back from complete collapse, the happier I am.  I want to have time to get myself North.

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Re: Latest PIOMAS update (July)
« Reply #64 on: July 04, 2013, 07:31:14 PM »
T not kk3 if you are being picky in SI (no stacking allowed). ;)

M for thousand and MM for million if you stack prefixes American style.

If usage is loose it could be a thousand or a million of anything and if the magnitude isn't clear from the context you should always ask the user to clarify rather than assume they are using it the same way you are. M on its own is seriously ambiguous when used across cultures.

????? As an engineer M stands for mega, which is 10^6 or one million.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #65 on: July 04, 2013, 07:36:32 PM »
No chance of beating 2012 now, as Neven has pointed out over on his blog (in comments) this year underlines the importance of the spring melt. It's so important that if it's missed it generates the appearance of a recovery.

Bob Wallace

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Re: Latest PIOMAS update (July)
« Reply #66 on: July 04, 2013, 08:06:32 PM »
2) This year's currently higher volume isn't due to thicker ice in the middle of the pack, but later-melting ice at the fringes;

3) That ice at the fringes is going to melt anyway, as it does nearly every year;

4) Extent and area have both indicated over the past several days that insolation is finally catching up, and they're starting to drop in earnest;

I hope Wipneus doesn't mind me linking to his excellent new regional maps in this comment.  But they see to be the perfect way to illustrate what Jim is saying.





It looks to me that the CAB might not be doing as well this year as it was last.  Take a look at the Area chart.  As long as the CAB is melting at close to the 2012 rate then the horse race is not over.  The other two regions in which we might expect some remaining ice are the Greenland Sea and Canadian Archipelago.  GS is ahead of last year and CA about tied.

jdallen

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Re: Latest PIOMAS update (July)
« Reply #67 on: July 04, 2013, 08:10:15 PM »
No chance of beating 2012 now, as Neven has pointed out over on his blog (in comments) this year underlines the importance of the spring melt. It's so important that if it's missed it generates the appearance of a recovery.

Not so sure of this conclusion yet.  The early July losses have been shockingly large.  Looking at holes opening up in the <b>center</b> of ice covered areas, I am left with serious concern regarding the ice's durability.

I'm also wondering about wide swaths of extent that are showing up "brown" - it seems like these are weaker still.

That said, I hope you are right, Chris.
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Neven

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Re: Latest PIOMAS update (July)
« Reply #68 on: July 04, 2013, 08:20:18 PM »
No chance of beating 2012 now,

The chance is small.  :)
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Bob Wallace

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Re: Latest PIOMAS update (July)
« Reply #69 on: July 04, 2013, 08:26:51 PM »
No chance of beating 2012 now

It looks like there's a decent chance of a big hole opening up in the CAB.  That happens and 2012 is in for a struggle. 

It's all about the CAB. 

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #70 on: July 04, 2013, 09:01:17 PM »
No chance of beating 2012 now, as Neven has pointed out over on his blog (in comments) this year underlines the importance of the spring melt. It's so important that if it's missed it generates the appearance of a recovery.

Not so sure of this conclusion yet.  The early July losses have been shockingly large.  Looking at holes opening up in the <b>center</b> of ice covered areas, I am left with serious concern regarding the ice's durability.

I'm also wondering about wide swaths of extent that are showing up "brown" - it seems like these are weaker still.

That said, I hope you are right, Chris.

July volume losses are large but...

From 30 June to minimum losses have a small downward trend from 1979, then a step drop post 2010, i.e. late summer losses are decreasing (see below). Not increasing. It remains to be seen whether 2013 will be in the pre or post 2010 set.

2010 to 2012 average loss 8.24k km^3.
1979 to 2009 average loss 9.88k km^3.
1979 to 2009 trend -0.0214x + 10.227.

Jim Pettit

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Re: Latest PIOMAS update (July)
« Reply #71 on: July 04, 2013, 10:51:28 PM »
From 30 June to minimum losses have a small downward trend from 1979, then a step drop post 2010, i.e. late summer losses are decreasing (see below). Not increasing.

That's my point. Those post-June drops have been getting increasingly smaller over the years for the simple reason that more fringe ice has melted out earlier. And that hasn't happened this year. Now, my "theory" will obviously be proved wrong if SIA stays a million km2 or so above 2013. But I'm willing to be money that it won't. I'm not saying either area or volume will necessarily catch 2012--but by by the same token I don't think the odds of a record this year are nearly as remote as some are expressing. And I do think it's far too early to call it a day and shove 2013 into the "recovery" column.

(I'll revisit and recalculate at the end of July; if volume then is over, say 8,000 km3, I'll admit my mistake and be happy. But I've a feeling end-of-July volume will be closer to 6.5-6.8k. And if it is, look out.)


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Re: Latest PIOMAS update (July)
« Reply #72 on: July 04, 2013, 11:26:02 PM »
Jim,

This I exactly why I noted: "It remains to be seen whether 2013 will be in the pre or post 2010 set."

However apart from 2008, every post 2007 year has shown an increase in anomalies post June, and the 2008 decrease in June was modest. I also think that the final levelling tendency in the PIOMAS anomalies for late June 2013 is significant, such an inflection is seen in all post 2007 years. Which implies to me that the drop in anomalies is done this year, as has been the case in other post 2007 years.

Neven

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Re: Latest PIOMAS update (July)
« Reply #73 on: July 04, 2013, 11:35:00 PM »
I'm posting a PIOMAS update tomorrow or the day after that, because I want my latest post to remain at the top of the main page a bit longer.

At the danger of being accused that I express doubt because as an alarmist I don't like the data (2013 being almost 2000 km3 higher than 2012), but could PIOMAS have trouble getting to grips with this year that could be seen as the first year of the New Abnormal era that perhaps started last year? I know the weather has caused an extremely slow start, but volume as high as 2010?

I'm not really expressing doubt, as I've always stressed the uncertainty in PIOMAS output because it's a model, especially when numbers plummeted. I'm just entertaining the possibility, but will have to think about how I'm going to put it into words tomorrow.
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Bob Wallace

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Re: Latest PIOMAS update (July)
« Reply #74 on: July 04, 2013, 11:49:10 PM »
What I'd love to see is regional volume graphs.  Like the extent and area above.

It looks to me that all regions but the CAB will melt out.  More precisely, the ice currently in all other regions will melt out.  The Greenland Sea and CA will likely be replenished somewhat by ice currently in the CAB.  (Beaufort is getting a late start, but it has a two month cushion based on 2012 hitting zero by the end of July.)

It could be that CAB volume for 2013 is already lower than for 2012.  If that's the case and weather from here on out contributes about the same amount of melt then it's a new record.


BornFromTheVoid

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Re: Latest PIOMAS update (July)
« Reply #75 on: July 05, 2013, 01:05:20 AM »
Something to note, the recent NSIDC update said that CryoSat found the average thickness this March to be 8% less than March 2012. http://nsidc.org/arcticseaicenews/

This didn't appear to be the case with PIOMAS in March.

dree12

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Re: Latest PIOMAS update (July)
« Reply #76 on: July 05, 2013, 03:43:34 AM »
I'm posting a PIOMAS update tomorrow or the day after that, because I want my latest post to remain at the top of the main page a bit longer.

At the danger of being accused that I express doubt because as an alarmist I don't like the data (2013 being almost 2000 km3 higher than 2012), but could PIOMAS have trouble getting to grips with this year that could be seen as the first year of the New Abnormal era that perhaps started last year? I know the weather has caused an extremely slow start, but volume as high as 2010?

I'm not really expressing doubt, as I've always stressed the uncertainty in PIOMAS output because it's a model, especially when numbers plummeted. I'm just entertaining the possibility, but will have to think about how I'm going to put it into words tomorrow.

I believe it. It was really cold this spring, far colder than in 2011 or 2012. In addition to the rapid refreeze last year, it was enough to bring volume far up.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #77 on: July 05, 2013, 07:43:19 AM »
With regards the weather I agree with Dree12.

The large ref-freeze was merely a result of record low ice at the end of last season. But as I've shown in my blog posts on the atmospheric set up in June, the spring melt being far less marked this year was not a surprise in view of the weather. And as the spring melt sets the melt season in the years 2010 to 2012 that we are now above 2012 in volume is quite believable to me.

Steven

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Re: Latest PIOMAS update (July)
« Reply #78 on: July 05, 2013, 12:33:13 PM »
I'm not really expressing doubt, as I've always stressed the uncertainty in PIOMAS output because it's a model, especially when numbers plummeted. I'm just entertaining the possibility, but will have to think about how I'm going to put it into words tomorrow.

Neven, I would be careful indeed to pick the right words.  By the way, many commenters on the ASIB blog will mention this issue anyway :)

The Beaufort ice was thin at the start of the melting season.  But the ice has been compressing towards the coasts.

The divergence (and thinning?) in the Arctic Basin have moved ice volume towards the fringes.

Melt pond formation and albedo drops have been way behind schedule.  Insolation has been wasted. 

Altogether, I still believe PIOMAS.
« Last Edit: July 05, 2013, 05:59:47 PM by Steven »

TerryM

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Re: Latest PIOMAS update (July)
« Reply #79 on: July 05, 2013, 04:25:53 PM »
Neven
Your pessimism may be justified. PIOMAS does well when melt is from the edges under clear skies. Whether the same can be said when melt consists of thinning from the center under clouds & fog is still to be seen.
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Neven

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Re: Latest PIOMAS update (July)
« Reply #80 on: July 06, 2013, 12:15:45 AM »
I just posted PIOMAS July 2013 on the ASIB.

Conclusion:
Right now I'm not sure what to make of that big gap between 2013 and previous years. If it's real, this could mean that 1) the start of the melting season is of paramount importance, and 2) 2013 is a recovery year, the first one in 5 years, volume-wise. More or less the same conclusion I drew a couple of days ago, after reviewing maps showing atmospheric circulation patterns in May and July.

But I think I'm seeing a huge melting potential out there, despite those slow start weather conditions, with holes in the interior of the ice pack and lots of discoloured, thin ice on the fringes. We mustn't forget that this melting season started with the most first-year ice on record. A bad start can postpone much of that ice to melt out, but all bad starts come to an end.

I believe there will be a rapid area/extent decrease in the coming weeks, and it remains to be seen how PIOMAS is going to interpret that. If, like I said, some of those parameters are sidetracked due to the unique pattern of this melting season so far, they just might get back on track once the melting season throws off its mask.


That last one about throwing off the mask, is pretty good, if I say so myself. That will probably be turned into a subtitle for the ASI update in two weeks from now.  8)
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dree12

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Re: Latest PIOMAS update (July)
« Reply #81 on: July 06, 2013, 01:06:50 AM »
I just posted PIOMAS July 2013 on the ASIB.

Conclusion:
Right now I'm not sure what to make of that big gap between 2013 and previous years. If it's real, this could mean that 1) the start of the melting season is of paramount importance, and 2) 2013 is a recovery year, the first one in 5 years, volume-wise. More or less the same conclusion I drew a couple of days ago, after reviewing maps showing atmospheric circulation patterns in May and July.

But I think I'm seeing a huge melting potential out there, despite those slow start weather conditions, with holes in the interior of the ice pack and lots of discoloured, thin ice on the fringes. We mustn't forget that this melting season started with the most first-year ice on record. A bad start can postpone much of that ice to melt out, but all bad starts come to an end.

I believe there will be a rapid area/extent decrease in the coming weeks, and it remains to be seen how PIOMAS is going to interpret that. If, like I said, some of those parameters are sidetracked due to the unique pattern of this melting season so far, they just might get back on track once the melting season throws off its mask.


That last one about throwing off the mask, is pretty good, if I say so myself. That will probably be turned into a subtitle for the ASI update in two weeks from now.  8)


I think that PIOMAS is not far off. Looking at the thickness charts, the post-2010 era has been relatively stable. The curves for 2010, 2011, and 2012 are not far off from each other—and 2013 is closely following them as well. The arctic may possibly have reached a lower limit on annual thickness, and further volume declines may be in the form of area declines, rather than ice thinning. If this hypothesis verifies, then the PIOMAS figure is likely accurate only because area is not lower than 2010.

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Re: Latest PIOMAS update (July)
« Reply #82 on: July 06, 2013, 09:04:19 AM »
PIOMAS is doing exactly what I'd expected in June given the other data I'd been following.

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Re: Latest PIOMAS update (July)
« Reply #83 on: July 06, 2013, 09:04:21 AM »
I think that PIOMAS is not far off. Looking at the thickness charts, the post-2010 era has been relatively stable. The curves for 2010, 2011, and 2012 are not far off from each other—and 2013 is closely following them as well. The arctic may possibly have reached a lower limit on annual thickness, and further volume declines may be in the form of area declines, rather than ice thinning. If this hypothesis verifies, then the PIOMAS figure is likely accurate only because area is not lower than 2010.

I don't think I can agree.  Ice bridge observations earlier this year suggested large areas of ice were considerably thinner than what is being modeled. Unfortunately, we won't be able to get a sense of who's right for a few weeks yet...
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Richard Rathbone

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Re: Latest PIOMAS update (July)
« Reply #84 on: July 06, 2013, 03:54:14 PM »
I don't think I can agree.  Ice bridge observations earlier this year suggested large areas of ice were considerably thinner than what is being modeled. Unfortunately, we won't be able to get a sense of who's right for a few weeks yet...

Have you got a reference with the detailed calculations for that comparison? My impression was that they were in decent agreement. I read that ice bridge observations noticed thin ice corresponding to refrozen cracks, but that's a lot of thin lines, not a lot of thin area.

jdallen

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Re: Latest PIOMAS update (July)
« Reply #85 on: July 06, 2013, 07:01:06 PM »
I don't think I can agree.  Ice bridge observations earlier this year suggested large areas of ice were considerably thinner than what is being modeled. Unfortunately, we won't be able to get a sense of who's right for a few weeks yet...

Have you got a reference with the detailed calculations for that comparison? My impression was that they were in decent agreement. I read that ice bridge observations noticed thin ice corresponding to refrozen cracks, but that's a lot of thin lines, not a lot of thin area.

Someone have the nice Ice Bridge link handy which shows the estimated thickness under their flight paths?  Best way to determine if my perception is wrong.
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Re: Latest PIOMAS update (July)
« Reply #86 on: July 06, 2013, 07:53:42 PM »
I tried to make a point a few days ago, and may have miscommunicated it, so I hope you don't mind if I try again, only with some simplification--and some new art.

That point was that over the years, total annual volume loss has remained fairly constant, with a yearly average of between 16.5k and 17.0k km3 disappearing from maximum to minimum. The "death spiral" is, thus, not due to increasingly greater melt, but is in fact almost entirely the product of decreasing annual maxima.

That being said, then, I threw together this dual plot showing volume losses from each year's maximum through June 30, and from July 1 through each year's minimum. And it's plain to see that, as the years have gone by, there's increasingly been more of the former and less of the latter. In fact, because of that c. 16.75k km3 average, there exists in most cases a loose inverse relationship: more early melt means less later melt, and vice versa.



Now, the 2013 volume maximum was the lowest on record yet (though admittedly not by much). And between that maximum and June 30, the amount of ice lost was less than it's been for a number of years. My estimation, then, is that the post-June loss this year will be greater than it's been for a number of years. And because of that, the 2013 volume minimum will be lower than some are predicting. Again, I'm not necessarily saying we'll see a new record (although that's certainly well within the bounds of possibility). I'm just saying that this year will show once again that any "recovery" is purely imaginary.

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Re: Latest PIOMAS update (July)
« Reply #87 on: July 06, 2013, 08:05:36 PM »
PIOMAS and IceBridge.
http://farm8.staticflickr.com/7385/9225201142_446243a2e6_o.png

This isn't the ideal way to do an intercomparison, far from it. But I've yet to motivate myself to get round to programming it, as I hate programming (I like results, but I've not yet been sufficiently motivated by the prospect of these results).

I've used a schematic of IceBridge (IB) thickness transects from here.
http://www.arcus.org/search/seaiceoutlook/2013/june
See 'Pan Arctic'.

This has been scaled and overlaid onto one of my PIOMAS thickness plots. My PIOMAS plot is in 25 cm increments, however 2m is 1.75 to 2m, so each thickness band is the upper limit of the band.

One important point: Note that from March to April there is thickening, the PIOMAS gridded data is monthly average and shows the 'effective thickness' for each grid box.

Beaufort is seen to be 1.5 to 1.75m (dark band along the Alaskan coast) rising to 1.75 to 2m further into the pack. In the same region towards Chukchi greens predominate in IB suggesting around 1.5m, but we don't know whether the flights occurred in early or late April, and as stated above, due to thickening between March and April averages this matters.

There is a suggestion of thicker ice in Beaufort near Banks Island in IB data, but in the central blue pack IB suggests reds and oranges (about 2 to 3m), here PIOMAS is 2.5m and above.

Given the approximate nature of the comparison, I think the two are in reasonable agreement.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #88 on: July 06, 2013, 09:09:54 PM »
Jim,

Considering the volume loss from June 30 to min, using the average from 2007 to 2009 applied to the volume at 30 June 2013 predicts a volume minimum of 3.25k km^3. Whereas using the average volume loss from 2010 to 2012 applied to volume on 30 June 2013 predicts a volume minimum of 4.76k km^3, higher than 2010!

So we're on track to at least meet 2012 volume, which suggests we'll have a similar area/extent record.... But, the situation isn't quite so clear.



Volume loss from maximum to 30 June for 2013 is between that for 2007 to 2009 and 2010 to 2012. So which camp will 2013 fall into?

I had been going to put this in my recent blog post, but somehow it got published before it was ready, and this got left out, I'll tidy that up tomorrow. But as it's germane to your point:

Call the volume loss from Max to 30 June 'Early'. Call the volume loss from 30 June to Min 'Late'. Calculate the ratio Late/Early. Now plot on a scatter plot as a function of the Early volume loss, and calculate the best fit.



Now the above equation can be used to calculate the ratio of Early and Late given 2013's Early volume loss. After which the ratio can be applied to the Early volume loss of 2013 to calculate what we should expect the Late volume loss of 2013 to be, this can then be subtracted from volume at 30 June 2013.

This method predicts a minimum volume of 4.57k km^2.

ghoti

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Re: Latest PIOMAS update (July)
« Reply #89 on: July 06, 2013, 11:50:42 PM »
Isn't plotting a value against a ratio with the same value as the numerator an auto-correlation? As the numerator decreases the ratio also decreases if there is no correlation of the numerator to the denominator ( I think).

If you plot early versus late i'm pretty sure you will not get a significant correlation. This would suggest early melt doesn't predict late melt - within limits after all since if you melt all the ice early the late melt would have to be small.

Interesting either way. I'm just leery of ratios from what I found with them in my plant research many years ago.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #90 on: July 07, 2013, 09:31:48 AM »
Ghoti,

My maths isn't great, but plotting early vs late produces a greater scatter and lower R2 so the increase of R2 may be the autocorrelation at work. The reason I considered it reasonable is that it's the same sort of technique used in Hubbert Linearisation.
http://en.wikipedia.org/wiki/File:HubbertLin_US_Lower48.svg

Richard Rathbone

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Re: Latest PIOMAS update (July)
« Reply #91 on: July 07, 2013, 12:48:28 PM »
Ghoti is right. Its ones of the sins my supervisor warned me about.

Hubbert linearisation is a better descriptor than predictor. The results from using it to predict future oil production are a lot poorer than you'd think from looking at the graphical fit. That is partly down to the fit not actually being as good as it looks because the way the variables are plotted enhances it.

If you have good reasons for the expression you are plotting you can use this sort of plot to fit a parameter, but you need to establish that its the right thing to plot by other means first. The reason for using a Hubbert linearisation isn't that its a good fit, but that there are reasonable grounds for expecting oil production to follow a logistic curve.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #92 on: July 07, 2013, 02:10:35 PM »
Thanks Ghoti and Richard,

There is no way to predict, as a straight scatter plot doesn't give a good fit at all. 2010 to 2012 look more like a regime shift, with years before giving a wide scatter.
« Last Edit: July 07, 2013, 05:19:02 PM by ChrisReynolds »

Wipneus

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Re: Latest PIOMAS update (August)
« Reply #93 on: August 04, 2013, 06:44:07 AM »
Updated, graphs are in the top post.

slow wing

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Re: Latest PIOMAS update (August)
« Reply #94 on: August 11, 2013, 04:37:10 AM »
I'm wondering if there is going to be a poll for PIOMAS minimum volume?


We already have them for minimum area and minimum extent...  :P


slow wing

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Re: Latest PIOMAS update (August)
« Reply #95 on: August 18, 2013, 03:13:04 PM »
It would be fantastic if someone who knows how would be kind enough to do the PIOMAS sea ice thickness maps for the July data...  :)

Dave C

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Re: Latest PIOMAS update (August)
« Reply #96 on: September 01, 2013, 06:23:37 PM »
Thanks for keeping all these charts updated. Just a quick suggestion- Your "Monthly Average Arctic Ice Volume" chart would be much easier to read if you divided it into two charts, Oct-Mar and Apr-Sep.

Wipneus

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Re: Latest PIOMAS update (August)
« Reply #97 on: September 01, 2013, 06:52:55 PM »
Thanks for keeping all these charts updated. Just a quick suggestion- Your "Monthly Average Arctic Ice Volume" chart would be much easier to read if you divided it into two charts, Oct-Mar and Apr-Sep.
Perhaps I will do something like that (during the freezing season). It is definitely not clearest of graphs.

ChrisReynolds

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Re: Latest PIOMAS update (August)
« Reply #98 on: September 01, 2013, 08:55:35 PM »
It would be fantastic if someone who knows how would be kind enough to do the PIOMAS sea ice thickness maps for the July data...  :)

Sorry Slow Wing, missed this when you posted. The gridded data on which thickness maps are based has not been updated since June.

slow wing

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Re: Latest PIOMAS update (August)
« Reply #99 on: September 02, 2013, 04:00:36 AM »
Thanks for letting me know, Chris, much appreciated.


The next update is going to be very interesting!