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Author Topic: Latest PIOMAS update (May 2019)  (Read 937163 times)

Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #650 on: July 09, 2015, 06:29:05 PM »
It can also be reduced by high amounts of snow cover, insulating the newborn first year ice.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #651 on: July 09, 2015, 06:42:25 PM »

Lower September extent leads to greater growth - the growth thickness feedback again.

Why?
It is a statement that I often see, but after years of lurking still do not comprehend from an energy budget point of view.
I would expect that ice growth is mostly depending on the energy in the system. If we have a low September extent we have a lot of energy in the system that needs to get out before we can have substantial ice growth.
Same if we have a warmer than average winter. Again we have an energy system that is not favourable for ice growth.
Additional energy is also entering the Arctic in winter due to higher sea water temperatures in the gulf stream and other currents.
So why do we expect a large volume growth when we reach a low September extent if we have a energy system that is not in equilibrium and an Arctic where the average winter temperatures are increasing significantly?

Back to lurking now.....

Oren has already answered it but...

Calculate the autumn/winter month to month PIOMAS volume changes for 1979 to 2015, get the preceding September extent data for each year. Then take each annual series of month to month volume gain, and the series of September minimum and calculate as interannual averages.

So for each month you have a series of interannual differences in volume increase, and you have interannual difference in the preceding September extent. Correlation of the resulting timeseries has the following result.

Nov   -0.592   99.95% confidence
Dec   -0.685   99.95% confidence
Jan   -0.575   99.95% confidence
Feb   -0.656   99.95% confidence
Mar   -0.452   99.5% confidence
Apr   -0.471   99.5% confidence

In other words, as the September extent goes down the autumn/winter volume gains go up, and this can be asserted with high confidence. Note that I just had to work this out because it is so obvious I have not kept a spreadsheet with this data.

You might then proceed to think that this is interesting.

You could examine the physics of sea ice growth.
http://dosbat.blogspot.co.uk/2015/01/the-simplest-model-of-sea-ice-growth.html

And from that you could transform your simple model in terms of growth as a function of initial thickness.
http://dosbat.blogspot.co.uk/2015/01/the-slow-transition-thickness-growth.html

You would find a very good agreement with what a complex model like PIOMAS reproduces, and that where the agreement fails other processes are at work.

If you want to understand things from an energy budget point of view you must do the physics and use the maths to develop understanding. Trying just to reason with words will invariably result in the wrong answer.


ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #652 on: July 09, 2015, 06:47:15 PM »
Plinius,

The ability of the ocean to vent heat to the atmosphere in the cold of winter after the sun goes down must not be underestimated. Heat flux from leads measured in winter has been observed to be over 1kW/m^2. Even 2012 with very late refreeze then went on to the largest volume gain from September to April.


NeilT

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Re: Latest PIOMAS update (July)
« Reply #653 on: July 09, 2015, 10:40:53 PM »
Chris,  here is my problem with PIOMAS and let me see if I can get it exactly right.

If we take the season from 2011 maximum to 2011 minimum, to 2012 maximum, to 2012 minimum, to 2013 maximum.

Then we compare max PIOMAS
Then we go to the CT area and confirm the comparable maximum area and the comparable minimum area in the following

2011 max/min
2012 max/min
2013 max

We should be able to see the corresponding volume loss of the 2012 huge extra melt reflected in the 2013 max ice PIOMAS.

Because whatever we melted more than the 2011 minimum must have been more than first year ice.  Let us be generous and say 2.5m instead of 2m FYI which will be created to replace that which was lost in that 2012 record area minimum.

Let's be even more generous and assume that the difference between 2012 max area and 2013 max area (2013 being bigger), is actually MYI instead of FYI.  I'm doing this because it makes the calculations easier for me.

What we should see, were PIOMAS estimating correctly, is the difference between the MYI area lost in the exceptional melt and the FYI ice area which replaced it at the 2013 max.

Follow me so far?

So to the calculations.

2011 Max area was 12.99m mkm^2 on April 6th
2011 Min area was 2.9899m mkm^2 on 24 Aug

2012 Max area was 13.70m mkm^2 on  on 28 March
2012 Min area was 2.6399m mkm^2 on on 26 Sept

2013 Max area was 13.79m mkm^2 on on 26 Feb
Although this area peaked again at 13.79 on 14 Mar

OK so to PIOMAS
 
2011 max volume was 22.5mkm^3 average for April
2012 max volume was 23.11mkm^3 average for April
2013 max volume was 23.12mkm^3 average for April

Now here's the thing that blows me away and makes me fail to trust PIOMAS

2011 - 2012 I can understand.  It was clearly more volume and it was roughly in April that the volume was largest.

OK so why 2013

2012 had an area low 350kkm^2 lower than 2011.  That means that 350kkm^2 of MYI melted to be replaced with FYI.

OK on my rules above, 2013 was 90kkm^2 higher than 2012 so we remove that and get a figure of 260kkm^2 more FYI than MYI in the 2013 maximum, compared to the 2012 maximum.

So at the postulated 0.5m thickness, that's 130kkm^3 additional volume lost in the 2012 summer melt which has to be replaced by the 2013 re-freeze.

OK, again, that is within the bounds of variance for a colder winter.  Except that the winter was exceptionally slow to start for 2012/13 in terms of area.  2012 was lower than 2011 almost all the way to the year end.  2013 started much lower than 2012 until mid Jan where they crossed over.

Which means, the FYI in 2013 was thinner than the FYI in 2012.

So I don't understand how we get a max ice volume some 10kkm^3 larger than 2012.  All logic tells me that it should be at least the 130kkm^3 lower if not more because of the slow FYI generation.  Although I could be wrong on that.

Finally I can't align the PIOMAS data with the area calculations over the months.

2013 peaked on Feb 26th then remained high till Mar 14th.  It then fell from that date all the way to the end of April.  In fact April ended 1.85mkm^2 lower than the 14th March maximum.

Yet the PIOMAS figures for Feb, Mar and April 2013 were 19.318,   21.964 and 23.122 respectively.

The only answer I have for this is "It's a model".

But my point is this.  If it can get that situation wrong, then what did it do with the rest of it and since.  It may be that the averaging mechanism within the model does balance out.

But here's the final kicker.  A lot of what melted out in 2012 was not 2.5m ice. There was a lot of 3,4 and 5 year ice vanished that year.  It wasn't 350*0.5 It was a hell of a lot more.  Also it was not predominantly 2m FYI ice which replaced the lost ice from 2012 but a lot of 1M and 1.5M ice at the periphery.  I do recall that because of this very thin ice there was an expectation that 2014 would be another serious loss year.

If we add all this together, it should mean that PIOMAS by now is seriously off in it's calculation.

Or I got it all wrong and there is a simple explanation as to why FYI on a short warm winter can replace all the MYI volume lost in an exceptional melt year????


 
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Tor Bejnar

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Re: Latest PIOMAS update (July)
« Reply #654 on: July 09, 2015, 11:36:58 PM »
Part of the answer is probably how much did or did not get exported during each winter.  See Chris's
Quote
You would find a very good agreement with what a complex model like PIOMAS reproduces, and that where the agreement fails other processes are at work.
Arctic ice is healthy for children and other living things.

NeilT

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Re: Latest PIOMAS update (July)
« Reply #655 on: July 10, 2015, 12:03:50 AM »
As Neven said on the latest updates.  There was HUGE export in 2012 and much of it was old MYI.  I remember that myself.
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anotheramethyst

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Re: Latest PIOMAS update (July)
« Reply #656 on: July 10, 2015, 07:33:22 AM »
Chris,  here is my problem with PIOMAS and let me see if I can get it exactly right.

If we take the season from 2011 maximum to 2011 minimum, to 2012 maximum, to 2012 minimum, to 2013 maximum.

Then we compare max PIOMAS
Then we go to the CT area and confirm the comparable maximum area and the comparable minimum area in the following

2011 max/min
2012 max/min
2013 max

We should be able to see the corresponding volume loss of the 2012 huge extra melt reflected in the 2013 max ice PIOMAS.

Because whatever we melted more than the 2011 minimum must have been more than first year ice.  Let us be generous and say 2.5m instead of 2m FYI which will be created to replace that which was lost in that 2012 record area minimum.

Let's be even more generous and assume that the difference between 2012 max area and 2013 max area (2013 being bigger), is actually MYI instead of FYI.  I'm doing this because it makes the calculations easier for me.

What we should see, were PIOMAS estimating correctly, is the difference between the MYI area lost in the exceptional melt and the FYI ice area which replaced it at the 2013 max.

Follow me so far?

So to the calculations.

2011 Max area was 12.99m mkm^2 on April 6th
2011 Min area was 2.9899m mkm^2 on 24 Aug

2012 Max area was 13.70m mkm^2 on  on 28 March
2012 Min area was 2.6399m mkm^2 on on 26 Sept

2013 Max area was 13.79m mkm^2 on on 26 Feb
Although this area peaked again at 13.79 on 14 Mar

OK so to PIOMAS
 
2011 max volume was 22.5mkm^3 average for April
2012 max volume was 23.11mkm^3 average for April
2013 max volume was 23.12mkm^3 average for April

Now here's the thing that blows me away and makes me fail to trust PIOMAS

2011 - 2012 I can understand.  It was clearly more volume and it was roughly in April that the volume was largest.

OK so why 2013

2012 had an area low 350kkm^2 lower than 2011.  That means that 350kkm^2 of MYI melted to be replaced with FYI.

OK on my rules above, 2013 was 90kkm^2 higher than 2012 so we remove that and get a figure of 260kkm^2 more FYI than MYI in the 2013 maximum, compared to the 2012 maximum.

So at the postulated 0.5m thickness, that's 130kkm^3 additional volume lost in the 2012 summer melt which has to be replaced by the 2013 re-freeze.

OK, again, that is within the bounds of variance for a colder winter.  Except that the winter was exceptionally slow to start for 2012/13 in terms of area.  2012 was lower than 2011 almost all the way to the year end.  2013 started much lower than 2012 until mid Jan where they crossed over.

Which means, the FYI in 2013 was thinner than the FYI in 2012.

So I don't understand how we get a max ice volume some 10kkm^3 larger than 2012.  All logic tells me that it should be at least the 130kkm^3 lower if not more because of the slow FYI generation.  Although I could be wrong on that.

Finally I can't align the PIOMAS data with the area calculations over the months.

2013 peaked on Feb 26th then remained high till Mar 14th.  It then fell from that date all the way to the end of April.  In fact April ended 1.85mkm^2 lower than the 14th March maximum.

Yet the PIOMAS figures for Feb, Mar and April 2013 were 19.318,   21.964 and 23.122 respectively.

The only answer I have for this is "It's a model".

But my point is this.  If it can get that situation wrong, then what did it do with the rest of it and since.  It may be that the averaging mechanism within the model does balance out.

But here's the final kicker.  A lot of what melted out in 2012 was not 2.5m ice. There was a lot of 3,4 and 5 year ice vanished that year.  It wasn't 350*0.5 It was a hell of a lot more.  Also it was not predominantly 2m FYI ice which replaced the lost ice from 2012 but a lot of 1M and 1.5M ice at the periphery.  I do recall that because of this very thin ice there was an expectation that 2014 would be another serious loss year.

If we add all this together, it should mean that PIOMAS by now is seriously off in it's calculation.

Or I got it all wrong and there is a simple explanation as to why FYI on a short warm winter can replace all the MYI volume lost in an exceptional melt year????

it does seem strange.  in my infantile understanding of all this, ice volume appears to be among the harder characteristics to measure, and i've seen a lot of dubious looking claims about bolyme and ice thickness.

that said, i don't think you should throw the model away out of hand.  i was under the impression that one of the reasons 2012 was possible was that there were large volume drops in 2010 or 2011.  second, open water freezes faster and thicker than water covered with thin or low quality ice.  people on this forum have shown that detrended data reveals no correlation between arctic maximum and minimum, and i see no reason to believe a minimum would predict the following maximum.  six months is just too long for one single variable to have an affect in such a dynamic system.

all the models and measurements have their flaws.  the best we can do is take all the info from multiple sources and use them to construct a "most likely" picture of the arctic right now.  if piomas isn't working for u today, don't use it, but that doesn't mean u should stop checking it altogether.  six months from now, it might be the most accurate model, you just never know.

Michael Hauber

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Re: Latest PIOMAS update (July)
« Reply #657 on: July 10, 2015, 10:40:12 AM »
Perhaps the amount of melt in the next month or two will give an indication of how accurate PIOMAS is.  PIOMAS suggests that current volume and thickness is similar to 2007.  Currently weather conditions seem about as extreme as 2007.  If PIOMAS is correct and conditions continue we should see a minimum about 2007 levels.  If PIOMAS is seriously overestimating volume then we may see a final extent/area minimum like 2012 or even lower.
Climate change:  Prepare for the worst, hope for the best, expect the middle.

plinius

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Re: Latest PIOMAS update (July)
« Reply #658 on: July 10, 2015, 04:07:29 PM »
Plinius,

The ability of the ocean to vent heat to the atmosphere in the cold of winter after the sun goes down must not be underestimated. Heat flux from leads measured in winter has been observed to be over 1kW/m^2. Even 2012 with very late refreeze then went on to the largest volume gain from September to April.

@Chris: This is exactly the point! Just the other way round. Currently the heat flux per area of leads is high because they feed a bitingly cold and dry atmosphere.  However, we are not talking leads, but a 10Mio. sqkm open patch of ocean. If I did not toss away some units: If you now assume that through that boundary of about 10000km the air in the ground layer flows in with a height of roughly 1 km, I get that the total heat loss from that would be around 1W per m/s and K of that flow. Not so big any more...

The radiative losses are what will likely dominate an ice free arctic, since you have troubles bringing so much cold air in. So, how large are those radiative losses? The net upwelling radiation from a water layer near freezing is less than 300 W/m^2.  If you protect that thing with a fog layer at -10 celsius, you end up somewhere around 50W/m^2. With that kind of assumption you are at 90 days to produce 1m of ice... If you create such a huge open basin, you have to examine the prediction very closely how much radiative loss you still produce.

We have already seen smaller things like the Hudson bay troubled to freeze over. Will be way worse if the arctic is open and has time to accumulate heat during the summer months.

Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #659 on: July 10, 2015, 06:07:39 PM »
The net upwelling radiation from a water layer near freezing is less than 300 W/m^2.  If you protect that thing with a fog layer at -10 celsius, you end up somewhere around 50W/m^2. With that kind of assumption you are at 90 days to produce 1m of ice...

The problem is once you have 1/4 meter of ice (20 days?), you no longer have open water, so what does that mean for the fog layer?

Steven

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Re: Latest PIOMAS update (July)
« Reply #660 on: July 10, 2015, 06:28:49 PM »
Which means, the FYI in 2013 was thinner than the FYI in 2012.

No.  The first-year ice in spring 2013 was thicker than the FYI in spring 2012.

The first several months of 2013 were relatively cold compared to recent years in the Arctic (e.g. see here for the January to May average).  Sea level pressure was relatively high, so probably there were clear skies most of the time.  And I guess snow depth was relatively low.  That means conditions were favorable for sea ice volume growth during winter/spring 2013.

See also Neven's 2012/2013 Winter Analysis.

CryoSat agrees with PIOMAS in this case, in the sense that it agrees that sea ice volume in spring 2013 was similar to spring 2012.  E.g. see here (scroll down to the section about sea ice thickness):

Quote
With these assumptions, updated radar freeboard and sea-ice thickness maps of the CryoSat-2 data product from the Alfred Wegner Institute (Fig. 4.4) show an increase in average freeboard of 0.05 m in March 2014 compared to the two preceding years (2012: 0.16 m, 2013: 0.16 m, 2014: 0.21 m). This amounts to an increase of mean sea-ice thickness of 0.38 m (2012: 1.97 m, 2013: 1.97 m, 2014: 2.35 m). The mean values were calculated for an area in the central Arctic Ocean where the snow climatology is considered to be valid. Excluded are the ice-covered areas of the southern Barents Sea, Fram Strait, Baffin Bay and the Canadian Arctic Archipelago.

« Last Edit: July 10, 2015, 09:07:32 PM by Steven »

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #661 on: July 10, 2015, 06:45:31 PM »
Plinius,

The ability of the ocean to vent heat to the atmosphere in the cold of winter after the sun goes down must not be underestimated. Heat flux from leads measured in winter has been observed to be over 1kW/m^2. Even 2012 with very late refreeze then went on to the largest volume gain from September to April.

@Chris: This is exactly the point! Just the other way round. Currently the heat flux per area of leads is high because they feed a bitingly cold and dry atmosphere.  However, we are not talking leads, but a 10Mio. sqkm open patch of ocean. If I did not toss away some units: If you now assume that through that boundary of about 10000km the air in the ground layer flows in with a height of roughly 1 km, I get that the total heat loss from that would be around 1W per m/s and K of that flow. Not so big any more...

The radiative losses are what will likely dominate an ice free arctic, since you have troubles bringing so much cold air in. So, how large are those radiative losses? The net upwelling radiation from a water layer near freezing is less than 300 W/m^2.  If you protect that thing with a fog layer at -10 celsius, you end up somewhere around 50W/m^2. With that kind of assumption you are at 90 days to produce 1m of ice... If you create such a huge open basin, you have to examine the prediction very closely how much radiative loss you still produce.

We have already seen smaller things like the Hudson bay troubled to freeze over. Will be way worse if the arctic is open and has time to accumulate heat during the summer months.

At some stage in the latter part of this century this will be very significant, and the winter ice will be in serious decline. But even with the staggering warming of recent years the decline in winter freezing degree days is relatively modest.



This results in a modest decline in equilibrium thickness for thermodynamic growth from open water (Sept to April). Note that the limiting factor in ice growth is not currently time needed to grow, it is the winter cold.

Take this graphic from Thorndike 1975.


Note how massive the growth rate from open water to 1m thick ice is. This is a result of the massive heat flux through thinner ice, and is then limited as the ice grows thicker. This is so powerful that weather and late freeze factors have a relatively small impact on peak winter ice thickness.

Andreas T

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Re: Latest PIOMAS update (July)
« Reply #662 on: July 10, 2015, 06:50:51 PM »
Plinius,

The ability of the ocean to vent heat to the atmosphere in the cold of winter after the sun goes down must not be underestimated. Heat flux from leads measured in winter has been observed to be over 1kW/m^2. Even 2012 with very late refreeze then went on to the largest volume gain from September to April.

@Chris: This is exactly the point! Just the other way round. Currently the heat flux per area of leads is high because they feed a bitingly cold and dry atmosphere.  However, we are not talking leads, but a 10Mio. sqkm open patch of ocean. If I did not toss away some units: If you now assume that through that boundary of about 10000km the air in the ground layer flows in with a height of roughly 1 km, I get that the total heat loss from that would be around 1W per m/s and K of that flow. Not so big any more...

The radiative losses are what will likely dominate an ice free arctic, since you have troubles bringing so much cold air in. So, how large are those radiative losses? The net upwelling radiation from a water layer near freezing is less than 300 W/m^2.  If you protect that thing with a fog layer at -10 celsius, you end up somewhere around 50W/m^2. With that kind of assumption you are at 90 days to produce 1m of ice... If you create such a huge open basin, you have to examine the prediction very closely how much radiative loss you still produce.

We have already seen smaller things like the Hudson bay troubled to freeze over. Will be way worse if the arctic is open and has time to accumulate heat during the summer months.
My doubt about that fog layer in arctic night is that the top of the layer radiates out to space at its temperature which either is as cold as the top of the ice is now which probably means precipitation or it is warmer and radiates more strongly requiring more heat input from below to stay at that temperature.
These are the reasons why people have developed models, there are interdependent processes at work which can't be quantified in isolation.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #663 on: July 10, 2015, 07:05:58 PM »
Neil T,

I'm having problems following what you are trying to say, so sorry if I get it wrong.

Does it all come down to:

1) Winter 2013 should have reflected the volume loss in 2012.
2) You can't align area and volume.
3) PIOMAS volume goes up when area declines after March.

If I am correct in that presumption your answers are:

1) The growth thickness feedback.

2) You can only align volume and area using thickness, and you'll get nowhere with CT Area. It produces weird 'compactness' as shown in CAPIE, and I found very quickly that while NSIDC Extent and Area work fairly neatly with PIOMAS (though not perfectly), CT Area is quite bonkers - that's why I stopped using it! The best way to use PIOMAS and area is to use their area.h and .heff files for area (concentration of ice) and thickness respectively.

3) Area loss from March onwards comes from thin ice outside the Arctic Ocean, meanwhile the Arctic Ocean is still sub zero and volume of ice within the Arctic Ocean continues to increase after the area maximum. Indeed the volume within the Central Arctic peaks in May!

Gray-Wolf

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Re: Latest PIOMAS update (July)
« Reply #664 on: July 10, 2015, 08:31:56 PM »
Quick question. How well does the PIOMAS team cope with 'rotten ice'? We've all seen the floes from the 'aloft cam' come late August so we know some pretty raggerty ice makes it through the year ( to be in filled with FY ice over winter) so would we not expect the FY ice to melt out leaving the old carcass behind? Would this not leave a lot of 'Swiss cheese ice' over July/Aug? Would such not mean the volume tends high over such regions?
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plinius

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Re: Latest PIOMAS update (July)
« Reply #665 on: July 10, 2015, 08:40:08 PM »
Chris: Your point of massive growth rates from Thorndike 1975 is null, since that is simply based on a cold arctic and single patches. Of course you lose giant amounts of heat from a lead or a small patch of thin ice. I would also say that a loss of ~10% of the freezing degree days that we have seen is _massive_, given the fact that current ice conditions have only very moderately affected the heat balance of the ocean.

@AndreasT: As far as I know the model situation is not fully conclusive concerning those parameters. Just too far out of our normal experience (and that of the models) and also quite a close call in energy balance, if there is a stable winter ice equilibrium. Look for Langlaufer's stuff, among other things.

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Re: Latest PIOMAS update (July)
« Reply #666 on: July 10, 2015, 08:47:25 PM »
Neil T,

I'm having problems following what you are trying to say, so sorry if I get it wrong.

Does it all come down to:

1) Winter 2013 should have reflected the volume loss in 2012.
2) You can't align area and volume.
3) PIOMAS volume goes up when area declines after March.

If I am correct in that presumption your answers are:

1) The growth thickness feedback.

2) You can only align volume and area using thickness, and you'll get nowhere with CT Area. It produces weird 'compactness' as shown in CAPIE, and I found very quickly that while NSIDC Extent and Area work fairly neatly with PIOMAS (though not perfectly), CT Area is quite bonkers - that's why I stopped using it! The best way to use PIOMAS and area is to use their area.h and .heff files for area (concentration of ice) and thickness respectively.

3) Area loss from March onwards comes from thin ice outside the Arctic Ocean, meanwhile the Arctic Ocean is still sub zero and volume of ice within the Arctic Ocean continues to increase after the area maximum. Indeed the volume within the Central Arctic peaks in May!
The major problem is, our instrumentation to measure thickness directly is very sparse, and the tools we have to gather it by inference (e.g. Satellite microwave) subject to high degrees of variability.   Extent and area can be directly measured, volume only inferred. As a result, our confidence intervals are quite broad.

I'm sure the people taking the measurements are quite aware of it, and the significantly diverging estimates of thickness and volume by various institutions is mute testament to it.

Those estimate will tend to close up as our sampling increases and tools improve, but until then we will have to accept both uncertainty and occasional surprises.
This space for Rent.

ktonine

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Re: Latest PIOMAS update (July)
« Reply #667 on: July 10, 2015, 09:14:28 PM »
Extent and area can be directly measured, volume only inferred.

It would be an interesting endeavor to do so, but alas we do not measure either directly.  We infer ice concentration/extent/area from satellite measurements of brightness temperature. At least 7 different algorithms have been used to try and differentiate ice from water using brightness temperature as a proxy.

Perhaps when the remaining ice is down to a single floe we can send a surveying team out to measure the area directly.

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Re: Latest PIOMAS update (July)
« Reply #668 on: July 10, 2015, 09:16:56 PM »
But they'll have to hurry...
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Re: Latest PIOMAS update (July)
« Reply #669 on: July 10, 2015, 10:09:09 PM »
Quick question. How well does the PIOMAS team cope with 'rotten ice'? We've all seen the floes from the 'aloft cam' come late August so we know some pretty raggerty ice makes it through the year ( to be in filled with FY ice over winter) so would we not expect the FY ice to melt out leaving the old carcass behind? Would this not leave a lot of 'Swiss cheese ice' over July/Aug? Would such not mean the volume tends high over such regions?

PIOMAS assimilates concentration of sea ice from NSIDC.

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #670 on: July 10, 2015, 10:11:01 PM »
Chris: Your point of massive growth rates from Thorndike 1975 is null, since that is simply based on a cold arctic and single patches. Of course you lose giant amounts of heat from a lead or a small patch of thin ice. I would also say that a loss of ~10% of the freezing degree days that we have seen is _massive_, given the fact that current ice conditions have only very moderately affected the heat balance of the ocean.

 ::)

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Re: Latest PIOMAS update (July)
« Reply #671 on: July 10, 2015, 11:40:13 PM »
Extent and area can be directly measured, volume only inferred.

It would be an interesting endeavor to do so, but alas we do not measure either directly.  We infer ice concentration/extent/area from satellite measurements of brightness temperature. At least 7 different algorithms have been used to try and differentiate ice from water using brightness temperature as a proxy.

Perhaps when the remaining ice is down to a single floe we can send a surveying team out to measure the area directly.
Hah! True enough; that said, the granularity of those samples provides far higher precision than we have when measuring volume.

I like your reply as well, Neven...
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iceman

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Re: Latest PIOMAS update (July)
« Reply #672 on: July 11, 2015, 01:22:26 PM »
In recent years the volume anomaly has consistently bottomed in late June or July.  2015 could be an exception, with several factors pointing toward an extended decline:
   -  sustained heat over the MYI north of Canadian Archipelago
   -  fragmentation around the big floes in Beaufort
   -  winds pushing other thick ice near the Atlantic edge into Kara and Barents
   -  an uptick in Fram export a week or so from now
   -  a lobe in southern Laptev that looks to be cut off from the main pack in a few weeks
   -  and as Neven mentioned on the blog, easy ice left in Hudson and Baffin Bay
My guess is for a low in August, with volume anomaly dropping in between the 2010 and 2013 traces.

plinius

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Re: Latest PIOMAS update (July)
« Reply #673 on: July 13, 2015, 04:28:37 PM »
Well, the one thing with which PIOMAS could really give a good view on the detailed quality of the model is publishing the necessary ex post corrections. I.e. statistics about where and how much the ice has to be removed from the model, where it has really melted out, and where and how much it melts out in the model, but not in reality. Not aware that such statistics would exist publicly, correct?

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Re: Latest PIOMAS update (July)
« Reply #674 on: July 13, 2015, 06:04:05 PM »
Neil T,

I'm having problems following what you are trying to say, so sorry if I get it wrong.

Does it all come down to:

1) Winter 2013 should have reflected the volume loss in 2012.
2) You can't align area and volume.
3) PIOMAS volume goes up when area declines after March.

If I am correct in that presumption your answers are:

1) The growth thickness feedback.

2) You can only align volume and area using thickness, and you'll get nowhere with CT Area. It produces weird 'compactness' as shown in CAPIE, and I found very quickly that while NSIDC Extent and Area work fairly neatly with PIOMAS (though not perfectly), CT Area is quite bonkers - that's why I stopped using it! The best way to use PIOMAS and area is to use their area.h and .heff files for area (concentration of ice) and thickness respectively.

3) Area loss from March onwards comes from thin ice outside the Arctic Ocean, meanwhile the Arctic Ocean is still sub zero and volume of ice within the Arctic Ocean continues to increase after the area maximum. Indeed the volume within the Central Arctic peaks in May!

Hi Chris,

Yes that does answer it for me.  Although I'd challenge the part about

Quote
Area loss from March onwards comes from thin ice outside the Arctic Ocean, meanwhile the Arctic Ocean is still sub zero and volume of ice within the Arctic Ocean continues to increase after the area maximum

Because if you need that area to create volume, then if it's really thin how did we get to a volume higher than 2012??  Given that much MYI was melted and flushed in 2012 and replaced with FYI.

FYI simply can't be MYI, there is not enough time for it to melt.

But, in general, you've answered my question.  PIOMAS is using a different area calc which would give different values which would tend to change the results.

I still think it's overestimating volume when significant portions of MYI are melted or flushed and replaced with FYI.  But, I guess, over time it would tend to average out if we didn't get another deep melt back.

I'll answer Steven separately.
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NeilT

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Re: Latest PIOMAS update (July)
« Reply #675 on: July 13, 2015, 06:09:13 PM »

Quote
The mean values were calculated for an area in the central Arctic Ocean where the snow climatology is considered to be valid. Excluded are the ice-covered areas of the southern Barents Sea, Fram Strait, Baffin Bay and the Canadian Arctic Archipelago.

Thanks for your post Steven.  But the conclusion I take from this is that the CAB, where the MYI melted, was replaced with slightly thicker FYI.

On the other hand, the other areas, which had a very short ice growth season, apparently, made up the rest of the lost MYI volume.

It doesn't make sense to me.  But I'm going to head back into watch mode.

I see almost the entire CAB in melt right now with huge intrusion into the CAB from the Pacific side.  Time will tell but the melt season is certainly under way in a big way.  What it results in will come down to both weather and current thickness.
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epiphyte

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Re: Latest PIOMAS update (July)
« Reply #676 on: July 14, 2015, 06:34:32 AM »
@ChrisReynolds - Thanks for following up on my post a few days back and apologies for not responding earlier...  real life is getting in the way of my ability to spend time on this stuff.

I stand corrected on the historical Feb-Mar growth numbers. What I should have said was that in the post 2000 period the modeled Feb-March gain has almost always been >~ 2M. Nonetheless, eyeballing the graph again, I can only see one 2000-2014 year (2003) when it was significantly less than that - so I think the point still has some validity..

Quote
  [...] 2015 was 1.75, not unusal. Lower September extent leads to greater growth - the growth thickness feedback again.

It still seems to me that that 1.75 *is* unusual -  later on you yourself mention that it is the third lowest on record  - and the lowest since 1995,

Quote
Quote
In other words, the January number is high enough to guarantee that the April number will be more than a million km3 *higher* than it was in 2014, absent worse than existing worst-case behavior in February and March.


Yes, it was 1.31 higher.

Quote
So we just lived through Feb - and to my eyes at least it looked as though it might indeed have have been the worst ever. Assume that PIOMAS cuts it's previous worst-case Feb growth in half (i.e. from ~2.5 to ~1.25m). If it did that the Feb number would be the same as it was last year.

Sorry, you lost me here, but February volume was 23.21, Jan Feb gain was 3.01 not unusual, Feb to Mar gain was 1.75 - towards the lower end of the distribution. 1993 (1.74), 1995 (1.52), were lower making 2015 Feb to Mar gain the third lowest on record.

Isn't it interesting though that 1995 went on to have a (then) record low Sep volume, as did 1993 - the other low Feb-Mar growth year which you call out above.

Even more interesting is that for both years the modeled September volume was much lower than the previous year (~2.3m - 2.5m below 1992 and 1994, respectively). I think I'm right in saying that 1981 is the only Sep-Sep drop larger than 2.5. apart from those two.

Quote
I'm sorry but I really don't get how you conclude Apr/May was/would be an 'incredible' i.e. unbelievable number. The PIOMAS April volume was as I said above 1.31 higher than in 2014, but area would be uninformative as this is concentrated in the thicker ice of the Central Arctic.

I think area is relevant because it enables a distinction between FYI growth and MYI growth. I think that the numbers are incredible because they require MYI to grow more quickly than it should.

2015 Sep volume was 1.5 higher than 2014.

If the starting and ending areas are the same and the and the starting volume was higher in year 2, then given the same weather conditions:

     1. the Overall volume growth should be less in year 2
     2. the FYI volume (i.e. FYI volume growth) should be the same for years 1 & 2
     3. the ending volume should be > ( starting volume + FYI volume) in both years.

what I was trying to say at the end of Feb was that in order to satisfy all of the above for the period sep 2014 - apr 2015, PIOMAS would need to come up with numbers which seemed inconsistent with either it's past behavior, or observed conditions at the time, or both.

you posted a temp. anomaly plot showing colder temps at the edges and warmer temps at the center - which IMO should disproportionately increase FYI over MYI growth, exacerbating the above. (mind you... I'm tired too :O )

ChrisReynolds

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Re: Latest PIOMAS update (July)
« Reply #677 on: July 14, 2015, 10:06:02 PM »
Neil, Epiphyte,

I'm sorry, but I hope you don't mind if I let your comments stand and don't address them. I've got a lot of maths to do for a project at work, and the sea ice is going to be a case of sit back and enjoy for the next few weeks.

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Re: Latest PIOMAS update (July)
« Reply #678 on: July 15, 2015, 08:38:41 PM »
Not in the slightest Chris. For me this is an interest and a diversion.  As a former analyst I just look at stuff and if it does not seem to make sense I ask why I can't make it make sense and keep asking questions to get my point over until I do understand why.

Work, as always, takes precedence.  Good luck with that.

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Benje

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Re: Latest PIOMAS update (July)
« Reply #679 on: July 25, 2015, 10:01:51 PM »
One thing that I think is important is how much ice volume we are losing each year....not just sea ice but from Greenland too ....because when we have lost the sea ice, if the same (or more!) annual heat is available in the area then we may expect the losses from Greenland to increase very rapidly: giving rise to much more sea level rise than we have seen up to now.

So I would like to see a combined graph of the total volume losses by year and, in an ideal world, with the sea level impact shown on one of the scales - perhaps from 2015 onwards (as well as the km cubed or GT values).

The losses from Greenland, say, since 2004 have been more than 3000Gt according to the  website
http://polarportal.dk/en/groenlands-indlandsis/nbsp/total-masseaendring/

The losses on Piomass since 2004 are between 3000 and 7000 km cubed per Wipneus (see below)...depending on which year!

I know it is to some extent using different sources of data for volume but isn't there a way to see the whole-loss picture.

I know that someone like Wipneus - or Chris or many other readers on this forum- would make a whole lot better job than me of combining the two.
Benje

https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd1.png?attachauth=ANoY7crpwhX-tfsSveSDHms2wPtbpPzWPYgjsNX0KJHC-w-_1_AScdyWtTapfJmQ_R3_s3Ez4x-FLeN2igsL0Ifhy8sQXjXt7tHGKOL9FbmjIezUaCBt1XJ4_S-uT7dKzPrdhA3JMzxyv7CA2MM_Me6YLcjew0G6jcbjVXdn5vp2L3sUuxsKK0cO_9JJQ802vipavkAEDQv8DGFpIdNvCQKtKlDvAg0UcGmssn3UZhmBbSQk7cDCUbKG-MMSWEdZTwStrV79t0Dy&attredirects=0

crandles

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Re: Latest PIOMAS update (July)
« Reply #680 on: July 26, 2015, 12:23:54 AM »
Aren't they rather different.

Sea ice volume in 2012 ranged from around 22k down to 4k km^3. When we have lost the sea ice in summer the range is then going to be from approx 19k down to 0 km^3 so instead of losing 18k km^3 we have extra heat which results in losing an extra 1k km^3 of sea ice and maybe the extra heat is a little more than 1k km^3 of ice melt resulting in some spill over into higher temperatures and more ice lost from greenland.

Adding different items together loses the detail.

The projections from climate models are that the losses of sea ice decline in rate as we approach virtually ice free. (Winters are long and cold and it is easy to build sea ice up to 20k km^3 in a winter if you start from having none.)

Whereas for Greenland we are talking increases in the rate of loss possibly even doubling every 10 years for a number of decades.

I suggest they are so different and have such different projected futures it really makes no sense at all to add them together.

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Re: Latest PIOMAS update (July)
« Reply #681 on: July 26, 2015, 08:00:06 AM »
Hi Crandles
Thanks for those comments
I was thinking of the (graphically) simpler situation of year on year loss. For example if the sea ice minumum movement year on year was added to the Greenland loss year on year then the true scale of ice loss over the years would be evident (its pretty much the same ice although the sea ice does have a bit of extra salt).
Benje

Neven

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Re: Latest PIOMAS update (July)
« Reply #682 on: July 26, 2015, 11:52:03 AM »
Greenland is losing 300 gigatonnes of ice on average. It doesn't grow back during winter, unlike sea ice. How much km3 is that? And how much km3 is average annual sea ice loss?

Other rather important point: When ice melts on Greenland, there's ice below it. When ice melts on the Arctic Ocean, there's open water below it.

My gut says the difference is orders of magnitude. Much more ice melts on Greenland, but sea ice loss causes much more albedo decrease. But that's my gut.
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Re: Latest PIOMAS update (July)
« Reply #683 on: July 26, 2015, 12:16:10 PM »
1 Gt is ~1.09 km^3 of ice.  To a first approximation we can just call that 1:1, which means Greenland is currently losing ~300 km^3 of ice per year.
http://www.sealevel.info/conversion_factors.html

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Re: Latest PIOMAS update (July)
« Reply #684 on: July 26, 2015, 12:21:40 PM »
1 Gt is ~1.09 km^3 of ice.  To a first approximation we can just call that 1:1, which means Greenland is currently losing ~300 km^3 of ice per year.
http://www.sealevel.info/conversion_factors.html

That's what I feared. So 300 km3 for Greenland that doesn't come back, and 20 km3 for sea ice that does come back. It's not useful to combine the two, Benje! But it never hurts to ask.  :)
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Re: Latest PIOMAS update (July)
« Reply #685 on: July 26, 2015, 12:27:49 PM »
The annual cycle for sea ice is of the order of 15-20 thousand km^3.

It's fairly intuitive to work out that the sea ice volume changes dwarf the changes on the Greenland ice sheet.

1)  The area of the Arctic ocean is much larger than the area of Greenland
2)  The thickness of Arctic sea ice changes by an average of a metre or more across the seasonal cycle
3)  The thickness of the Greenland ice cap doesn't fluctuate nearly that much during the seasonal cycle

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Re: Latest PIOMAS update (July)
« Reply #686 on: July 26, 2015, 12:34:09 PM »
However, the question was more about trends than the seasonal cycle.

Current trend in sea ice volume is a loss of 3000 km^3 per decade = 300 km^3 per year. So the year-on-year trend in Arctic sea ice volume is pretty much equal to the year-on-year trend in Greenland ice cap volume.  Nifty!
http://psc.apl.uw.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAnomalyCurrentV2.1.png

I think it's very misleading though to suggest that when the Arctic "bottoms out" at a summer volume of zero, there will be any neat numerical link to subsequent changes in GIS volume.  It's even plausible that GIS volume will go up for a while, due to extra moisture from Arctic evaporation leading to more snow deposition on Greenland.

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Re: Latest PIOMAS update (July)
« Reply #687 on: July 26, 2015, 12:40:43 PM »
The annual cycle for sea ice is of the order of 15-20 thousand km^3.

So much for my gut!  ;D

God, I'm stupid.  :-[
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Re: Latest PIOMAS update (July)
« Reply #688 on: July 26, 2015, 02:54:42 PM »
So much for my gut!  ;D

I can send some antacids.

 
  God, I'm stupid.  :-[

Not even close.
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Re: Latest PIOMAS update (July)
« Reply #689 on: July 27, 2015, 04:35:13 PM »
Thanks Peter for your comments and helpful clarifactions.

Obviously the future is tough to forecast ....whatever models or methods are used.

But history has happened and although difficult to measure, either the Greenland icesheet or the sea ice, "we" try pretty hard to understand the data we have. And the history is relevant, I suggest, with regard to the scale of heat (and scale of consequential ice loss) and with regard to the way that it is trending...accelerating  (which is what I think most of us fear) or whatever.

It is also relevant to look at both together because  the gross loss from Greenland divides into water run off and ice ...which becomes sea ice. It is probably difficult to measure the ice component but we can be sure that the accelerarting glaciers now provide an increasingly  material contrbution to the (now diminishing) sea ice volume.

I know that there might be more precipitation as snow on Greenland in a given year due to warmer moist air but it is the ice underneath which offers 7 metres of sea level rise (when melted) that is the big player here surely. Extra lubrication of the glaciers and inundation of the valleys with warm(ish) water in Greenland will surly hurry the ice decline.

I think that we should be very concerned that the absence of sea ice  will very soon allow substantial  latent heat absorbtion (previously by the sea ice as was)  to be transferred to the additional warming and ice loss from the Greenland ice sheet.

That's why I would like to see a chart of the two together: trouble is, I feel sure that I lack the skills of many of you to access and make compatible the appropriate data and to show the results in a complelling form. Absent any offers though, I will take it on but can anyone steer me to pre2004 data for the Greenland Ice sheet mass ...in an easy to access format?
Benje

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Re: Latest PIOMAS update (July)
« Reply #690 on: July 27, 2015, 11:59:28 PM »
I don't think there's any plausible mechanism whereby increased latent heat absorption by the Arctic Ocean can be transferred simply to cause additional ice loss from the Greenland ice sheet.  Can you give me a good reason why slightly warmer waters offshore in Barrow (say) should cause snowmelt in Cape Morris Jesup?

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Re: Latest PIOMAS update (July)
« Reply #691 on: July 28, 2015, 12:11:33 AM »
I don't think there's any plausible mechanism whereby increased latent heat absorption by the Arctic Ocean can be transferred simply to cause additional ice loss from the Greenland ice sheet.  Can you give me a good reason why slightly warmer waters offshore in Barrow (say) should cause snowmelt in Cape Morris Jesup?

Presumably it wouldn't if I'm right in where I think Barrow is, presumably however an earlier ice free Baffin bay would mean warmer hotter water beside Greenland and subsequently warmer hotter air that could blow over into greenland.

Writ large on for instance a potential year which is ice free by the start of August presumably that could have a large effect on greenlands melt due to the increased amount of heat picked up by the ocean no?


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Re: Latest PIOMAS update (July)
« Reply #692 on: July 28, 2015, 02:10:07 AM »
I don't think there's any plausible mechanism whereby increased latent heat absorption by the Arctic Ocean can be transferred simply to cause additional ice loss from the Greenland ice sheet.  Can you give me a good reason why slightly warmer waters offshore in Barrow (say) should cause snowmelt in Cape Morris Jesup?

Presumably it wouldn't if I'm right in where I think Barrow is, presumably however an earlier ice free Baffin bay would mean warmer hotter water beside Greenland and subsequently warmer hotter air that could blow over into greenland.

Writ large on for instance a potential year which is ice free by the start of August presumably that could have a large effect on greenlands melt due to the increased amount of heat picked up by the ocean no?
Not to mention direct ice-sheet/ocean interactions: http://www.whoi.edu/science/PO/people/fstraneo/ice-sheet-ocean-interactions .
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crandles

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Re: Latest PIOMAS update (July)
« Reply #693 on: July 28, 2015, 12:03:15 PM »
Presumably it wouldn't if I'm right in where I think Barrow is, presumably however an earlier ice free Baffin bay would mean warmer hotter water beside Greenland and subsequently warmer hotter air that could blow over into greenland.

But why not continue that and say where that warmer moister air gets colder and snows out the moisture?

Which effect dominates extra melting at the edges or extra snow in the interior?

nukefix

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Re: Latest PIOMAS update (July)
« Reply #694 on: July 28, 2015, 01:28:35 PM »
Absent any offers though, I will take it on but can anyone steer me to pre2004 data for the Greenland Ice sheet mass ...in an easy to access format?
Benje
Here's some, haven't looked at the format though:

http://imbie.org/data-downloads/

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Re: Latest PIOMAS update (July)
« Reply #695 on: July 29, 2015, 08:40:52 PM »
Thanks Nukefix: its an excel spreadsheet; perfect for me.
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Re: Latest PIOMAS update (July)
« Reply #696 on: August 02, 2015, 12:32:39 PM »
Now that the month is done (well, almost for the daily composites page), I decided to try and get a feel for which July is most comparable to July 2015. For my July analysis I have downloaded sea level pressure and temperature anomaly maps for 2007, 2010, 2011, 2012, 2013 and 2014. But July 2015 has been much warmer and sunnier, only 2007 comes somewhat close.

And so I decided to have a look at the biggest July droppers according PIOMAS (in km3):

2006: 5990
2007: 6421
2008: 6187
2009: 6750
2010: 6053
2011: 5938
2012: 5619
2013: 6245
2014: 5057

2007 was warmest and sunniest in my analysis, but it looks like 2009 was the biggest July dropper in the past decade. So, off I went to get the SLP and SAT maps, and here's how July 2007 and 2009 compare to July 2015 (up to July 30th):



July 2015 temperature anomaly is comparable to 2007, whereas average sea level pressure is similar to 2009. But overall July 2015 was sunniest and warmest in the 2006-2015 record, with the heat and sun smack in the middle of the area where ice is supposed to be thickest.

And so I expect PIOMAS to put July 2015 at a volume loss of at least 6500 km3, which will put it around 1000 km3 below 2014, and close the gaps with 2011, 2012, 2013.

Of course, it's 2013 that I'm interested in, as I've written a guest article for the Guardian website, stating that the rebound could be wiped out. This depends on August weather conditions, but also melting momentum, of course. 2013 lost relatively little volume during August.

If 2015 slips under 2013 by September, it's going to be tight.
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Yuha

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Re: Latest PIOMAS update (July)
« Reply #697 on: August 03, 2015, 10:40:36 AM »
And so I decided to have a look at the biggest July droppers according PIOMAS (in km3):

2006: 5990
2007: 6421
2008: 6187
2009: 6750
2010: 6053
2011: 5938
2012: 5619
2013: 6245
2014: 5057

2007 was warmest and sunniest in my analysis, but it looks like 2009 was the biggest July dropper in the past decade.

...

July 2015 temperature anomaly is comparable to 2007, whereas average sea level pressure is similar to 2009. But overall July 2015 was sunniest and warmest in the 2006-2015 record, with the heat and sun smack in the middle of the area where ice is supposed to be thickest.

This is supported by the mean temperatures in Alert:

     June July
2006 -0.6  3.7
2007 -0.4  2.4
2008  1.7  4.6
2009 -2.4  5.3
2010 -0.3  5.5
2011  2.9  2.9
2012  2.0  4.3
2013  0.7  2.3
2014 -2.2  1.8
2015  1.6  5.5
Avg   0.3  3.8


July 2015 was the warmest July tied with 2010.
And 2015 has had the warmest summer so far (June+July).

Nick_Naylor

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Re: Latest PIOMAS update (July)
« Reply #698 on: August 03, 2015, 01:35:42 PM »
You really have to throw out 2007 and 2009 though.  Once you do that, the correlation is pretty good ;)

Wipneus

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Re: Latest PIOMAS update (August)
« Reply #699 on: August 04, 2015, 08:16:51 AM »
New PIOMAS data is available. I have updated my graphs, see the top post.

(I did not see any updated gridded data yet. The thickness (change) maps will have to wait)