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Author Topic: What is the cause of the PIOMAS volume loss?  (Read 42496 times)

crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #50 on: January 27, 2014, 08:40:54 PM »
Rarely is an above average melt loss followed by a winter able to 'recover' the loss.

During a decline in volume, melts are generally larger than freezes so it is rare to get a 'recover the loss' particularly late on in the series.

A better way might be to calculate correlation of melt volume with previous freeze = 0.488
and correlation of freeze volume with previous melt = 0.603

Probably need to test the significance of the above difference.

If significant this would seem to suggest a large melt (with consequent low minimum) causes a large freeze is a more powerful relationship than a large freeze (with consequent high maximum) causes a large melt.

Trying to improve on that
If I look for correlation between distance above gompertz fit trend at maximum and size of following melt, I get 0.312
and compare to correlation between distance above trend at minimum and size of following freeze, I get -0.625

This pair of correlations works better, giving a larger difference though I am surprised at the 0.312 being positive.

Anyway best correlation is from distance above trend at minimum to following freeze.

Correlation doesn't prove causation however the suggestion, that the consequence of a larger than expected melt is for the freeze volume to increase, is what we would expect from thermodynamic reasoning of max volume approaching a thermal equilibrium.

Not sure if this gets us anywhere. The consequence of larger melts seems highly likely to be larger freezes by around 0.6* the melt increase. This is likely a feedback process, identifying what originally happened to start it off is more difficult.

Perhaps smaller freeze resulted in lower volume which caused larger melts and not quite so large freeze increases and feedback processes then kick in which makes the situation indistinguishable from the process being started by larger melts.

Or we could speculate the system was never in equilibrium but has always been lurching around due to things like medieval warm period, little ice age so that 'original cause' is not really meaningful.

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #51 on: January 27, 2014, 09:04:10 PM »
@ChrisReynolds - ocean heat flux is a factor I'm thinking about as well.  I think it applies during both melt and refreeze.  If you will, I think it proves the focus around which year over year variations play out.

The insolation and general mechanics of freeze and melt haven't changed, but point of symmetry between them has. I think the answer to why lies in the increasing balance of sensible heat over time.

I'll have to see about finding numbers for enthalpy changes over time, but that's where my hunch regarding ice loss lies.
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ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #52 on: January 27, 2014, 09:43:32 PM »
JD Allen,

See Korhonnen et al "Time and space variability of freshwater content, heat content and
seasonal ice melt in the Arctic Ocean from 1991 to 2011"
http://www.ocean-sci-discuss.net/9/2621/2012/osd-9-2621-2012-print.pdf
Quote
During the 2000s, freshening of the upper ocean is decreasing the depth of winter convection and the established stratification restricts, at least during summer, the upward mixing of Atlantic heat. Comparison of the hydrographic melt estimate to the potential ice melt obtained from reanalysed heat fluxes indicates that the seasonal ice melt rather reflects the variability in atmospheric heat fluxes than changes in the deep ocean heat content.

It was reading this (hat tip to Sidd) that made me have a last ditch effort to identify what season the losses were coming from.

The current discussion, interesting as it is, is academic. I framed the initial question of volume loss in terms of PIOMAS purposefully. The Lindsay & Zhang paper "The Thinning of Arctic Sea Ice, 1988–2003: Have We Passed a Tipping Point?" find that the recent (late 1990s onwards) loss of volume is due to the ice albedo effect, in summer.

Quote
Since 1988 the largest net change in the surface fluxes
compared to the mean values, amounting to the equivalent
of about 3 m of ice loss, is that due to the net solar
flux
(Fig. 8..). This loss is partially compensated by a
change in net longwave flux equivalent to about 2 m of
ice gain
, a large amount because of the heat lost from
the warmer open water or thin ice surfaces. The loss of
ice during this period due to ocean heat flux is about
2-m ice equivalent.
Some of this ocean heat is from the
solar heat absorbed by open water. Notably the change
in ice thickness due to changes in the turbulent sensible
and latent heat terms is relatively small. These fluxes
are largely determined by the air temperature (relative
to the ocean temperature), so the recent changes in the
mean ice thickness are not primarily due to recent
changes in the surface air temperature.


The increased net solar flux in the simulations can
only arise from changes in the model albedo because
the cloud fraction in the model, and hence the estimate
of the downwelling solar flux, has no interannual variability.

So the net loss of ice due to solar fluxes is 3m and this isn't due to clouds or changes in the sun as they're held constant, so it must be due to albedo changes. The ocean heat flux loss is 2m, but part of this is due to summer warming of the ocean due to the ice albedo feedback. But this is offset by a 2m gain in thickness due to increased emission of infra-red - the massive loss of heat each autumn in recent years comes to mind here.

A note before I continue - the Lindsay/Zhang paper seems (from its references) to be based on the first version of PIOMAS).

So combining those two papers: If the PIOMAS study reflects in broad scale the process that's been happening then the loss has been due to summer processes (I think it does) - the ice albedo feedback, with winter heat loss venting much of the accuumulated heat. Evidence for that latter statement is that the ice hasn't crashed to nothing after 2007. And Korhonnen's evidence indicates that during the summer the Atlantic Water isn't likely to interact with the melt process, indicating that it only interacts in Autumn/Winter when there's a large net output of heat into the atmosphere. And as the PIOMAS study indicates, and statistics and physics suggest (thickness/growth feedback) - the growth of ice happens in response to thin ice and low area of ice at the end of the previous season, less summer ice leads to more autumn/winter growth of ice. The evidence for this is from models (e.g. Tietsche et al), and the post 2007 increase in annual range.

Therefore it is unlikely that ocean heat flux is playing anything but a negligible role in the loss of sea ice.

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #53 on: January 27, 2014, 10:02:18 PM »
Kevin,

After what Crandles has said I'm beginning to wonder whether you've just confirmed what I've found with synthetic data sets and that there is no way to tell if the main volume loss is from freeze or melt - although as I say above the discussion is academic. I feel like Indecisive Dave from the Fast Show.

Crandles,

I'm less interested in initial cause than what process has caused the loss of volume, I'm satifsfied that it is ice albedo feedback (probably). It's worth recalling that Notz & Marotzke ruled out self acceleration for Extent, but they never looked at volume...

As for the ice being in equilibrium, the last time the ice was in a state similar to 2012 for protracted period was the Holocene Thermal Optimum (5k years ago), and that was under 40W/m^2 greater July 65degN insolation. I think it's fair to say it has been in a sort of equlibrium between then and now.

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #54 on: January 29, 2014, 08:37:10 PM »
Kevin, Crandles,

I've made my mind up about this...

Kevin said:

Quote
If we take the average of the Melt data and break the data set into those Melt seasons above and below average we find there is little correlation between low melt years and the following refreeze (0.181), but a stronger link between above average melt years and the following freeze (0.467).  More important, the average volume change for below average melt seasons and the following freeze is + 0.05, while the change for above average melt seasons and the following freeze is -0.76.

From this I think we can conclude that volume loss is due to above average melt seasons – despite above average freeze in the subsequent winter.

I agree. The freeze seasons following strong melts are dependent on the preceding melt, yet even in those years (April to following April) there is still a strong loss. Therefore it cannot be a weakness in the growth season.

Summing the melt seaon losses and freeze season gains and taking the difference reveals that for the above average years the overall loss due to dominance of the melt season is 11.509k km^3, for the below average years the same difference is a gain of 0.946. As stated in the initial post of this thread the total loss from Sept 1979 to Sept 2013 is 11.866k km^3. This implies that most of the volume loss has come from these above average years. I've tabled the above and below average years below.

Above and below average melts.
Year,   Above Avg,   Below Avg,
1980   ---------   15.925
1981   17.937   ---------
1982   ---------   15.468
1983   ---------   15.195
1984   ---------   15.705
1985   ---------   16.294
1986   ---------   14.863
1987   ---------   16.440
1988   ---------   16.214
1989   ---------   15.347
1990   ---------   16.090
1991   17.153   ---------
1992   ---------   14.565
1993   17.985   ---------
1994   ---------   15.877
1995   17.208   ---------
1996   ---------   13.495
1997   ---------   16.146
1998   17.795   ---------
1999   17.414   ---------
2000   ---------   16.074
2001   ---------   15.367
2002   16.587   ---------
2003   16.963   ---------
2004   ---------   15.716
2005   16.772   ---------
2006   ---------   16.002
2007   17.236   ---------
2008   17.75   ---------
2009   17.986   ---------
2010   18.658   ---------
2011   17.564   ---------
2012   18.358   ---------
2013   16.637   ---------

2013 can't be used because the 2013 freeze season data following the 2013 melt is not yet available.

I've re-run Kevin's stats, my answers are very slightly different. I get a correlation between melt period and following freeze period of: 0.477 for the above average years (15), 0.182 for the below average (18). The number of pairs in each correlation are given in brackets. For 15 data points statistical significance (95%) is 0.44, for 18 data points statistical significance (95%) is 0.40. Ref - bookmark this one it's useful.

So the above average melt correlation of 0.477 is statistically significant at the 95% confidence level (i.e. wrong only 5% of the time), while the below average correlation is not statistically significant.

Just sayin'  ;D
« Last Edit: January 29, 2014, 08:43:27 PM by ChrisReynolds »

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #55 on: January 30, 2014, 02:29:11 AM »
I've made my mind up about this...
...
So the above average melt correlation of 0.477 is statistically significant at the 95% confidence level (i.e. wrong only 5% of the time), while the below average correlation is not statistically significant.

Excellent and counter-intuitive analysis, Chris!

The additional implication might be, that the volume of refreeze is therefore similarly not a significant factor?

-J
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ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #56 on: January 30, 2014, 06:02:14 AM »
Chris,

Yes, I thought it was a clincher set of numbers :)

The actual correlations I had were 0.18146 and 0.476988 - I truncated the first to `0.181 and must have mistyped the 2nd.

There is a way to get the p-value in Excel, so there's no need for lookup tables.

=TDIST((pearson_cell*sqrt(N-2)/sqrt(1-(pearson_cell*pearson_cell))), N, tail)

Where pearson_cell is the cell containing the correlation value, N is the number of pairs of data, and tail is 1 or 2.

http://www.ehow.com/how_8554041_calculate-its-correlation-excel-2007.html
« Last Edit: January 30, 2014, 06:16:04 AM by ktonine »

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #57 on: January 30, 2014, 07:31:30 PM »
Kevin,

Yes I've used that before, but it's a bit complex, so I find that look up table easier to use. I suspected a typo.

JDAllen,

The volumes of melt and refreeze are nearly identical (very roughly 850k km^3 IIRC - I didn't keep the spreadsheet), it's just that the melt is smaller by about the same amount of overall loss).

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #58 on: January 30, 2014, 09:55:40 PM »
The volumes of melt and refreeze are nearly identical (very roughly 850k km^3 IIRC - I didn't keep the spreadsheet), it's just that the melt is smaller by about the same amount of overall loss).

So, if you will, the "symmetry point" between refreeze and melt is rising.  The question that comes to my mind then is, what sets of forces define that focus?  I'm not talking about the greenhouse gasses here, as their direct effect on ice formation or melt during any given year is negligible.
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ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #59 on: January 30, 2014, 10:52:51 PM »
During the Holocene Climatic Optimum about 5000 to 9000 years ago ice was around or lower than at present in the summer, this was due to much higher summer insolation.



So why is the sea ice declining now? Why is there this assymetry?

The Lindsay & Zhang paper tells us the recent (2000s) loss of volume is due to melt processes in the Summer. Kevin's reasoning leads to the same conclusion, note the clustering of above average melt seasons in the list I posted above in recent years.

However this is an incomplete explanation. If typically ice were biassed to loss then we'd see more evidence of reduction of ice than the evidence in the above graph summarises. Models provide a clue - only with anthropogenic forcing does the ice decline. The ice albedo feedback actually works both ways, with a forcing that slightly favours more ice, ice albedo feedback will amplify that and create more ice. With a forcing that acts against ice survival, ice albedo feedback acts to amplify the loss of ice.

Johannessen has shown that CO2 tracks the loss of sea ice in terms of annual average extent.



But look at the last few points, leading up to 2007, they're breaking away from the previous linear relationship towards more intense loss, and that graph is only from 1900 to 2007, it doesn't include the post 2007 period, which plays a big role in the volume loss. Note also that's annual average so is less affected by recession of ice within the Arctic Ocean, but is affected by winter extent recession, so it's a relationship more likely to bring out the effects of AGW.

The way I see it, CO2 and the resultant ocean and atmospheric warming with global warming is 'tipping the balance'. Without that we'd not see the extreme loss.

Does that answer your question?

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #60 on: January 31, 2014, 12:03:35 AM »
During the Holocene Climatic Optimum about 5000 to 9000 years ago ice was around or lower than at present in the summer, this was due to much higher summer insolation.



So why is the sea ice declining now? Why is there this assymetry?

The Lindsay & Zhang paper tells us the recent (2000s) loss of volume is due to melt processes in the Summer. Kevin's reasoning leads to the same conclusion, note the clustering of above average melt seasons in the list I posted above in recent years.

However this is an incomplete explanation. If typically ice were biassed to loss then we'd see more evidence of reduction of ice than the evidence in the above graph summarises. Models provide a clue - only with anthropogenic forcing does the ice decline. The ice albedo feedback actually works both ways, with a forcing that slightly favours more ice, ice albedo feedback will amplify that and create more ice. With a forcing that acts against ice survival, ice albedo feedback acts to amplify the loss of ice.

Johannessen has shown that CO2 tracks the loss of sea ice in terms of annual average extent.



But look at the last few points, leading up to 2007, they're breaking away from the previous linear relationship towards more intense loss, and that graph is only from 1900 to 2007, it doesn't include the post 2007 period, which plays a big role in the volume loss. Note also that's annual average so is less affected by recession of ice within the Arctic Ocean, but is affected by winter extent recession, so it's a relationship more likely to bring out the effects of AGW.

The way I see it, CO2 and the resultant ocean and atmospheric warming with global warming is 'tipping the balance'. Without that we'd not see the extreme loss.

Does that answer your question?

Thank you, Chris, mostly.  It certainly gives me more information to digest.  I consider it a given that CO2 forcing is providing the additional energy.  I guess my question is more on the order of, how is that energy being applied?  The ice is not melting as a direct effect of increased CO2.  I'm trying to understand the intermediate forces which change the point of symmetry around which the ice volume annually oscillates.

Albedo is most certainly one of those factors.  I imagine looking at what factors are included in climate models is the place to start, as well as looking at changes in heat in regions outside of the arctic.  For example...
-    Salinity
-    Net Ocean sensible heat
-    Heat transport
-    Atmospheric moisture
-    Changes in re-radiation

Not a new idea, I'm certain, but each of those can be broken down further, but perhaps by examining the assemblage, and looking at cyclical variations within them and how they line up, we may find hidden patterns, which give us more power of prediction?

It is a pity we don't have decent history of some of those factors much before 1970.
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ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #61 on: February 02, 2014, 09:43:51 AM »
I'm not quite saying that CO2 is giving the extra energy, in a system with feedbacks active much of the energy can come from the feedbacks. What the models show is that CO2 is biassing the ice/ocean system such that the feedback is able to drive the ice volume lower.

If you take ice volume as indicative of the energy gain (melting ice takes energy), then what Lindsay & Zhang shows is that in the feedback period (1995 to 2005) the ice loss is mainly due to ocean heat flux not atmospheric, in the melt season. They point towards the ice albedo feedback.

I'm taking this a step further and arguing the Kohonnen et al indicates that most of the ocean heat flux is due to ice albedo feedback not due to ocean warming, although I still think there's a small role for that. L&Z also show that in their model the preconditioning (1948 to 1989) is due to warming air temperatures, although in the real world there is equivocal evidence for this (which I suspect may be due to lack of data in land fast ice).

I've just been looking at NSIDC Extent and there's no clear link between the above/below average PIOMAS melts and either seasonal loss of volume or minimum at the end of the melt season, indeed NSIDC Extent at minimum for 2013 is high for recent years, depite an above average melt. I'm not sure how your idea could be taken further.

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #62 on: February 02, 2014, 10:10:13 AM »
Thank you, Chris.  I guess I can sum my reaction up as... My inner "systems analyst" thinks there are gaps in our understanding of the system, but is as yet at a loss to identify them. With more and better data hopefully will come greater illumination.
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Andreas T

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Re: What is the cause of the PIOMAS volume loss?
« Reply #63 on: February 02, 2014, 01:57:07 PM »
Chris, you quote Lindsay & Zhang as
Quote
...... Some of this ocean heat is from the
solar heat absorbed by open water. Notably the change
in ice thickness due to changes in the turbulent sensible
and latent heat terms is relatively small. These fluxes
are largely determined by the air temperature (relative
to the ocean temperature), so the recent changes in the
mean ice thickness are not primarily due to recent
changes in the surface air temperature.

The increased net solar flux in the simulations can
only arise from changes in the model albedo because
the cloud fraction in the model, and hence the estimate
of the downwelling solar flux, has no interannual variability.
There are two questions which this raises for me. The answers may be different for short term (yearly) and longer term consideration.
The amount of heat available from air in contact with the ice surface is of course determined by temperature and humidity of the air but also by the rate at which this air is replaced as its heat is tranfered to the ice, especially when melting/freezing and condensation mean heat is transferred without changing temperature. Would that not mean that wind patterns not only in the arctic but in its vicinity could have a significant influence even when that isn't reflected in temperatures?
The other issue is about clouds. I do not understand whether cloud fraction is fixed in the model as a set parameter but it has been said (I would like to know where data for this can be seen) that the summer of 2013 was cloudier than 2012 at times critical for the melt. So in this case interannual variability did occur.
Taking a global view, albedo effects of course affect the heat balance of the globe as a whole, shortwave radiation reflected is gone for good, changes in ocean or atmospheric heat fluxes move heat from one part of the globe to another. I.e. heat gained through radiation imbalance skewed by CO2 can be distributed unevenly but is going somewhere.  Greater or lesser heat input by albedo changes are additional terms in that balance. So it does matter where the energy for the melt is coming from.



ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #64 on: February 02, 2014, 02:48:29 PM »
Andreas,

The authors state:
Quote
The model is forced with daily fields of sea level air pressure (SLP) and 2-m air temperature (T2m) obtained from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis (Kalnay et al. 1996) for the 56-yr period 1948–2003...

...The specific humidity and longwave and shortwave radiative fluxes are calculated following the
method of Parkinson and Washington (1979) based on the SLP and T2m fields. The cloud fractions used to compute the downwelling radiative fluxes only have seasonal variability and no spatial or interannual variability.

With regards air temperature, yes it will have an effect, but the authors find it is not the driving process in the loss of volume from about 1995 onwards.

The summer of 2013 was cloudier, but the anomalies of the monthly rate of loss were still high in 2013. The problem in 2013 was that the season started with a large increase of volume (hence thickness) due to a cold May, I think a lot of the cold of 2013 was due to lack of melt, not the other way round. I discuss the issue further here:
http://dosbat.blogspot.co.uk/2014/01/post-2007-summer-melts-ice-or-atmosphere.html

Yes it does matter where the energy for the melt is coming from, I think that broadly speaking Lindsay and Zhang's model results apply to the real world. So I think that the volume losses since about 1995 are due to the ice albedo effect, but that a lot of the additional energy gained by the oicean is then being lost to the atmosphere in autumn (i.e. the Tietsche effect), which is why we haven't seen the ice crash to zero by now after the 2007 crash.

ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #65 on: February 02, 2014, 05:19:40 PM »
I've seen no one really account for ice temperature. There's buoy data, but they are few (and they're mobile) so  it's hard to make any historical comparison.   

But a 3 meter slab of ice that has a temperature of -2 C° on the bottom and -40 C° on top requires a lot more energy to melt than one defined by -2 C° and -25 C°.  Preconditioning is not just thickness, but temperature. 

So, not only is the ice thinner, it is also 'warmer' and even ice of the same thickness as in the past likely requires less energy to reach the melting point.  I think we'd find some interesting correlations between ice temperature and the records of extent and volume loss. 










ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #66 on: February 02, 2014, 09:26:04 PM »
If the arctic climate were in perfect balance then all of the melt in any given year would be replaced by an equal amount of freeze.  We would have a seasonal cycle that wouldn't necessarily be a sine wave, but it would be repeated year after year with equal amplitude minimums and maximums.

The fact that there is overall loss does NOT mean the process is driven by more melt - only that melt exceeds freeze. As I tried to explain, there are 3 possibilities mathematically (assuming the process is thermodynamic and the loss is not due to chaotic variability and the time window open to us just happens to be when the random chaotic features lead to a loss).

If we accept that the loss is a trend, and we know there are only 3 possible explanations, examination of the data tells us which of these possibilities is actually in effect - both melt and freeze are increasing, but melt is on average larger than freeze. But even knowing this does not tell us whether the losses are due to winter or summer processes.

We know that global warming does not just manifest itself in a particular month or season, but that does not mean that it's uniform.  Chris is actually asking (I think), Is the Arctic thermal balance more anomalous in winter or summer?  Arctic sea ice extent, area and volume anomalies are just indicators of this energy imbalance. 

The intuitive answer is that the losses are driven by summer melt processes.  The data seems to bear intuition out: The correlations between the preceding winter and summer melt are very low.  The correlations between melt and the following freeze are significant (though barely at 95% and with a small sample size).

BUT .... arctic winter warming is 4 times larger than summer warming! Hmmm .... back to the drawing board.

A consistent story has to mesh with all the facts.  The fact that winter warming is greater than summer warming in the Arctic is not, on its face, consistent with an explanation that says summer processes are responsible for the ice losses.

In looking for a freeze-melt correlation - and finding none - I believed the preceding winter's volume gain told us little about the summer melt losses.  This may be misleading.  Just because it's true doesn't actually prove anything.  What if volume gain isn't a particularly significant attribute of winter?

In fact, after a couple days reflection I believe that is actually the case - that volume gain per PIOMAS tells us very little about winter.  Arctic temperatures historically on average fall to -45 C°.  That's far lower than necessary to create ice.  There is also a thermodynamic limit to how thick sea ice can grow over the winter. So a 5 C° warming during winter may not lead to any less ice, but it will lead to more summer losses - since less energy is needed to raise the ice temperature to the melting point.

Take a look at the Interpolated surface OLR for February 2013 and compare it to previous Februarys.  One has to go back to at least 2004 to find anything similar.  Probably 2002 or earlier.  It's also pretty easy to show that the February OLR plots are very closely related to the summer losses.  Rank them in order just by visual appearance and you'll come out very close to the same order as the actual losses.

In summary, the fact that PIOMAS volume gains for the preceding winter do not correlate to summer losses is probably misleading.  We used this lack of correlation to prove to ourselves that winter didn't determine summer losses - but the lack of correlation only tells us that volume gain is not correlated to summer losses, not winter in general. 

The winter OLR plots, particularly January and February, tell a different story.  The OLR plots should be a rough proxy for ice temperature.  And there's a huge energy difference between melting ice that might be at -40 C° as opposed to ice that might be 'only' -30 C°.

Of course I reserve the right to change my mind - again :)
« Last Edit: February 02, 2014, 09:36:57 PM by ktonine »

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #67 on: February 02, 2014, 09:35:35 PM »
I've seen no one really account for ice temperature. There's buoy data, but they are few (and they're mobile) so  it's hard to make any historical comparison.   

But a 3 meter slab of ice that has a temperature of -2 C° on the bottom and -40 C° on top requires a lot more energy to melt than one defined by -2 C° and -25 C°.  Preconditioning is not just thickness, but temperature. 

So, not only is the ice thinner, it is also 'warmer' and even ice of the same thickness as in the past likely requires less energy to reach the melting point.  I think we'd find some interesting correlations between ice temperature and the records of extent and volume loss.

While it would *seem* that 15C should make a great deal of difference, the difference in sensible heat is pretty trivial in contrast to that required to force the phase change.  The only (and possibly significant) effect would be to shift timing at the start of the melt season by a few days.  From what I've seen of the buoy data, temperatures in thick ice can remain quite cold well into the melt season and don't appear to significantly impede melt.
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crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #68 on: February 02, 2014, 09:53:55 PM »

In summary, the fact that PIOMAS volume gains for the preceding winter do not correlate to summer losses is probably misleading.  We used this lack of correlation to prove to ourselves that winter didn't determine summer losses - but the lack of correlation only tells us that volume gain is not correlated to summer losses, not winter in general. 


Should you be using winter volume gain? Shouldn't it be whether max volume is above or below trend?

However I am a little confused. In calculating a correlation more ice volume at max seemed to cause more melting in the following melt season. However in calculating a formula, less ice volume seemed to cause more melting. Maybe I have just done something wrong, please check rather than taking my word for it. Perhaps what happens in the following melt season is different from the longer term effects?

ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #69 on: February 02, 2014, 10:26:11 PM »
jd - Using the heat of fusion of ice as 334 J/g  and the specific heat capacity of ice as 2.1 J/g.  A 5 C° change would require 10.5 J/g. or 3% more/less energy.  That is not insignificant.

Now, the ice is not a monolithic slab.  Temperature diffusion will make the percentage considerably smaller, but even if it only approaches 1% it would not be insignificant.  Consider, that a 2 C° change in the earth's temperature is about 0.7% in terms of energy.  We live in a very narrow temperature band in terms of energy.

crandles - "Should you be using winter volume gain? Shouldn't it be whether max volume is above or below trend?"

I'm not sure what max volume would tell us about winter either.  Volume could be above trend because there was a high initial value (at the end of summer) - not because of the winter process.  Remember, the goal is to separate summer and winter processes.  Chris was trying to use the volume gain/losses as proxies for the summer and winter processes.  I am now of the belief they (volume changes) are poor proxies for the summer and winter processes no matter how we transform them.  They are (IMHO) only proxies for the overall system, not the individual seasonal components.

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #70 on: February 02, 2014, 10:26:49 PM »
<snippage>
The intuitive answer is that the losses are driven by summer melt processes. 
<more snippage>
BUT .... arctic winter warming is 4 times larger than summer warming! Hmmm .... back to the drawing board.

A consistent story has to mesh with all the facts.  The fact that winter warming is greater than summer warming in the Arctic is not, on its face, consistent with an explanation that says summer processes are responsible for the ice losses.

... but I think summer processes are responsible is the correct conclusion, but possibly for counter-intuitive reasons.

<more snippage>
The winter OLR plots, particularly January and February, tell a different story.  The OLR plots should be a rough proxy for ice temperature.  And there's a huge energy difference between melting ice that might be at -40 C° as opposed to ice that might be 'only' -30 C°.

As I mentioned earlier, that 10C difference in sensible heat is 1/8th of that required to force the phase change from solid to liquid.  I'd further assert, that 10C difference is itself an effect tied back to a common cause, rather than itself a cause of additional melting.

Going back to your "sine wave" metaphor - over all, the variation in heat over any given year has not changed significantly, in spite of higher temperatures in the arctic.  What *has* changed, in a very significant way, is the net heat in the system, in particular Oceanic heat content. 

The effect of that, I think, is to shift the point at which the 'sine wave' crosses the threshold which divides conditions which support melt from conditions which support freeze.  This creates the *appearance*  of more summer melt.  The confusing part about more heat available in winter is, (as we have observed...) that it does not so much reduce the amount of ice produced by the refreeze, as much as it reduces the amount of heat *lost* through re-radiation during the refreeze.

Of course I reserve the right to change my mind - again :)

The clear sign of an inquisitive and sensible thinker. ;)
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ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #71 on: February 02, 2014, 10:33:14 PM »
jd - "I'd further assert, that 10C difference is itself an effect tied back to a common cause, rather than itself a cause of additional melting."

Of course, we know the overall answer is global warming.  Take that away and we have a stable system with random weather fluctuations.  We're just trying to parse out the mechanics - if possible - of how warming in the arctic manifests itself.  Are sea ice losses due to mainly summer processes, mainly winter processes, or is it a mix of the two - and if it is a mix of the two what percentage goes to each?

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #72 on: February 02, 2014, 10:47:26 PM »
jd - "I'd further assert, that 10C difference is itself an effect tied back to a common cause, rather than itself a cause of additional melting."

Of course, we know the overall answer is global warming.  Take that away and we have a stable system with random weather fluctuations.  We're just trying to parse out the mechanics - if possible - of how warming in the arctic manifests itself.  Are sea ice losses due to mainly summer processes, mainly winter processes, or is it a mix of the two - and if it is a mix of the two what percentage goes to each?

My assertion is neither - that the assignment of loss to winter or summer is illusory.  I'm afraid I'm not adequately describing what I think I see.  More heat available to the system overall has changed the the point at which seasonal variation in prompt heat input combines with residual heat to force the transition from net freeze to net melt.  For support for this, I'd be looking to see how we could make an effective determination of that event from previous seasons - the start of the refreeze in fall, and the start of the melt season in spring. 

As the arctic as a system itself is heterogeneous, and does not make that transition smoothly across regions, sorting this out could be a tall order.  A secondary metric might be rates of recovery/melt, and to see how those have changed as well. Suggestions?
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ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #73 on: February 02, 2014, 11:08:35 PM »
jd - "My assertion is neither - that the assignment of loss to winter or summer is illusory."

You've lost me completely.

The losses have to come from melt season, freeze season, or a combination of the two.  There's nothing illusory about that -- unless you believe the process isn't thermodynamic.

It may be that you meant the question of whether ice sea ice loss is attributable to summer or winter processes is irrelevant.  That may be true in the overall scheme of things, but that doesn't mean we can or cannot answer it :)

ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #74 on: February 02, 2014, 11:25:09 PM »
jd-
Quote
The confusing part about more heat available in winter is, (as we have observed...) that it does not so much reduce the amount of ice produced by the refreeze, as much as it reduces the amount of heat *lost* through re-radiation during the refreeze.

I think this is the reverse of what actually happens.  MORE heat is radiated to space, not less.  That's the negative feedback or what we call the Tietsche effect. 

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #75 on: February 03, 2014, 12:04:28 AM »
jd-
Quote
The confusing part about more heat available in winter is, (as we have observed...) that it does not so much reduce the amount of ice produced by the refreeze, as much as it reduces the amount of heat *lost* through re-radiation during the refreeze.

I think this is the reverse of what actually happens.  MORE heat is radiated to space, not less.  That's the negative feedback or what we call the Tietsche effect.

It makes sense - and you force me to correct myself.  My basic assertion should have been, that the increased winter heat, permits greater retention of heat year over year.  We may be radiating more, but I'm hypothesizing transport and increased capture is offsetting that negative feedback.

In a world without AGW, that would be the feedback that would regress the behavior of the system back to the mean.  With AGW, I think it is similarly "regressing back to the mean", but that "mean" - gross energy reserve - is steadily rising year over year.
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crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #76 on: February 03, 2014, 12:36:21 AM »
I'm not sure what max volume would tell us about winter either.  Volume could be above trend because there was a high initial value (at the end of summer) - not because of the winter process. 

I am inclined to disagree. The winter thickness approaches a thermal equilibrium thickness for much of the area such that the previous summer minimum does not matter much.

That equilibrium thickness is clearly getting less. I am only speculating on causes but the main ones would appear to me to be:

upward ocean heat flux
ghg levels
air temperatures


High air temperatures are mainly caused by thin ice and while they also cause ice to be thinner, I think much of the effect of higher temperatures has to be re-attributed elsewhere because the high air temperatures are mainly caused by thin ice. This leaves upward ocean heat flux and ghg levels though you can throw in others like atmospheric weather patterns and temperature of inflowing water....

To extent that Atlantic and Pacific warm water comes into contact with ice, these would have a quick effect. To extent they don't, then I am assuming there is likely to be prolonged effect over several years on the upward heat flux through heat diffusion.

Lindsay Zhang 2005 have warmer winter air temperature as the preconditioning and AO & PDO as the trigger.

I don't disagree with the AO and PDO potentially being the trigger that caused sufficient thin ice to get the summer albedo feedback going.

I am wondering if that trigger only had a small effect on the timing because ghg levels and upward ocean heat flux will be continuing to increase and this continues to cause thinner FYI and more FYI near Russia as less MYI makes it around the beaufort gyre flywheel. The thinner FYI and more of it causing higher air temperatures. Rather than as Lindsay Zhang have it that the higher temperatures cause the thinner ice.


ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #77 on: February 03, 2014, 02:40:23 AM »
crandles -
Quote
The winter thickness approaches a thermal equilibrium thickness for much of the area such that the previous summer minimum does not matter much.

I think this was one of the points I brought up regarding why ice volume gain is a poor proxy for winter conditions.  Over much of the area an average Jan/Feb temperature of -45 C° is indistiguishable from -35 C° if we're looking at volume gained.  But the latter will require less energy to melt out come summer (or the same amount of energy will melt more ice).

Otherwise I don't disagree with anything you wrote and share your skepticism that a trigger was really even needed.

crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #78 on: February 03, 2014, 12:24:59 PM »
Quote
-45 C° is indistiguishable from -35 C° if we're looking at volume gained

I accept than ice at -35C requires less heat to melt out than if it was at -45C. However, it looks like a fairly small effect to me.

Is it indistinguishable if we are looking at maximum thickness?

I think it is sensible to look at max volume or max thickness rather than volume gained because volume gained is essentially more noisy with extra noise coming from whether the previous minimum was high or low.

I think max thickness is distinguishable. The temperature is higher because the ice is thin and the ice is thin because upward ocean heat flux and ghg levels are high. If this wasn't the case then the thickness would adjust and we wouldn't be near an equilibrium thickness.

Trouble is, I don't see how to test this as data on upward heat flux is limited.

If max thickness is distinguishable then perhaps volume gained is also distinguishable albeit a little harder because of the extra noise.

ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #79 on: February 03, 2014, 02:31:12 PM »
crandles -
Quote
The temperature is higher because the ice is thin and the ice is thin because upward ocean heat flux and ghg levels are high. If this wasn't the case then the thickness would adjust and we wouldn't be near an equilibrium thickness.

Yes, no doubts here.   It may be possible to use thickness to derive seasonal attribution. To a large extent the OLR is a combination of winter temperatures and ice thickness.  So far I've only looked at OLR visually, but I may try and download the netcdf files and see what I can make of the data.

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #80 on: February 03, 2014, 08:13:22 PM »
Very interesting article just posted on the blog.  I must subscribe.

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2071.html

Implication is, we should look at lapse rate.
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ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #81 on: February 03, 2014, 08:25:18 PM »
JD Allen,

The current Arctic Amplification is largely due to loss of sea ice and snow cover. That paper is looking at the tropical side of the pole equator temperature gradient and finds processes that limit warming in the tropics.

***

I think it's been covered in the above discussion, but to be sure. There are sound physical reasonings underpinning the splitting of the year into freeze and melt seasons, at the thermodynamic core - in winter (freeze) heat flux is up through the ice and strongly so. This is not the case during summer.

I'm not convinced that the warming of ice is a strong factor. I see the transition to FYI from MYI as explaining most of the observations that in the past seemed to indicate ice warming. On which subject, I'm writing a blog post right now about the Spring Melt in PIOMAS post 2010 - that seems to be largely due to a shift to thinner ice in recent years.

ktonine

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Re: What is the cause of the PIOMAS volume loss?
« Reply #82 on: February 03, 2014, 10:03:17 PM »
Chris, as I mentioned above:
Quote
To a large extent the OLR is a combination of winter temperatures and ice thickness.

They're really two faces of the same coin.  Thin ice will allow more upward heat transfer making the ice and atmosphere above it warmer while very low surface temps will generate colder, thicker ice.

Even in years where we believe the thickness composition of the ice to be similar we can see significant differences in the OLR plots.  So while thickness definitely can affect surface temperatures the reverse is also true.  The differences between the 2012 and 2013 melt seasons were already evident in the OLR plots a month before the sun rose at 90N.


ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #83 on: February 03, 2014, 10:30:33 PM »
I think I said in my post on Siberian thinning and atmospheric warming that it wasn't a one way process, that the warming caused by thinner ice will reduce the equilibrium thickness.

Just checked, my closing comment:
Quote
So the close tracking of thinning and surface warming seems less likely to be due to warming affecting ice, and more due to thinning causing warming, although there is likely a feedback going on: Thinner ice warms the atmosphere which in turn reduces the thickness to which ice grows in the winter.

Because of this interdependency I think the only way to extract the various factors would be in a model where certain factors can be artificially held static.

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #84 on: February 03, 2014, 10:47:51 PM »
JD Allen,

The current Arctic Amplification is largely due to loss of sea ice and snow cover. That paper is looking at the tropical side of the pole equator temperature gradient and finds processes that limit warming in the tropics.

***

I think it's been covered in the above discussion, but to be sure. There are sound physical reasonings underpinning the splitting of the year into freeze and melt seasons, at the thermodynamic core - in winter (freeze) heat flux is up through the ice and strongly so. This is not the case during summer.

I'm not convinced that the warming of ice is a strong factor. I see the transition to FYI from MYI as explaining most of the observations that in the past seemed to indicate ice warming. On which subject, I'm writing a blog post right now about the Spring Melt in PIOMAS post 2010 - that seems to be largely due to a shift to thinner ice in recent years.

Yes, but it does contrast forces at work in the arctic as well.  On thing that stands out from a cursory review of their figures, is the much different forces and mechanisms at work.
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Dave C

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Re: What is the cause of the PIOMAS volume loss?
« Reply #85 on: February 04, 2014, 01:45:23 AM »
Pretty sure that paper is primarily about the arctic. I'm not at all qualified to assess its accuracy, but it's different enough from the standard albedo/ocean current assumptions that it's definitely worth looking into further.

http://news.yahoo.com/arctic-39-39-layer-cake-39-atmosphere-blamed-160858894.html

crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #86 on: February 04, 2014, 05:17:31 PM »
Pretty sure that paper is primarily about the arctic. I'm not at all qualified to assess its accuracy, but it's different enough from the standard albedo/ocean current assumptions that it's definitely worth looking into further.

http://news.yahoo.com/arctic-39-39-layer-cake-39-atmosphere-blamed-160858894.html

http://scienceblogs.com/stoat/2008/01/05/polar-amplification-again-1/

points out a post on realclimate by Jianhua Lu in 2008 that a 2007 paper by Jianhua Lu & Ming Cai had already shown that the temperature effects are greater than the ice albedo effect.

So it doesn't seem all that new or different. Just shows sea ice albedo feedback is much loved because it is easy to explain?

jdallen

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Re: What is the cause of the PIOMAS volume loss?
« Reply #87 on: February 04, 2014, 07:04:28 PM »

So it doesn't seem all that new or different. Just shows sea ice albedo feedback is much loved because it is easy to explain?

... But perhaps implies that the current temperature anomalies are good reason for increased pessimism regarding the coming melt season?
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ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #88 on: February 04, 2014, 07:54:08 PM »
Mmm...

Ice albedo feedback isn't directly the main player in the increased Arctic warming vs lower latitudes because during the summer temperatures are pegged low by melting ice. It's during Autumn/Winter that the highest Arctic temperature increases are found.

Dave,

I've not found a copy of the paper (without having to pay for it), but my reading of the abstract suggested suppresion of mid lat warming:
Quote
...the largest contribution to Arctic amplification comes from a temperature feedbacks: as the surface warms, more energy is radiated back to space in low latitudes, compared with the Arctic.
But the fact remains, the Arctic is warming much faster than the global average, and I'm not convinced this mid lat suppression is really the issue because of the massive warming in the Arctic.

Crandles linked to a Nature blog post, but that's about Graverson, which Screen & Simmonds have shown to be due to the reanalysis data used (IIRC), and that most of the warming actually comes from the surface. Again, this is not due to summer effects but due to anomalous venting of heat in autumn and winter over the Arctic Ocean.

I do recall correctly, from Screen & Simmonds, 2010, "The central role of diminishing sea ice in recent Arctic temperature amplification."
Quote
The findings of ref. 8 [Graverson et al] have been contested15,23–25, and concerns have been expressed over the validity of trends in ERA-40 that may reflect inhomogeneities or artefacts in the reanalysis rather than true climate signals23,24.

I should clarify here - The Pithan/Mauritsen paper is looking at AA in GCMs probably over a long period of projection. Screen and Simmonds are using contemporary data, which might explain part of the difference.

crandles

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Re: What is the cause of the PIOMAS volume loss?
« Reply #89 on: February 04, 2014, 11:56:28 PM »
Crandles linked to a Nature blog post, but that's about Graverson, which Screen & Simmonds have shown to be due to the reanalysis data used (IIRC), and that most of the warming actually comes from the surface. Again, this is not due to summer effects but due to anomalous venting of heat in autumn and winter over the Arctic Ocean.

In case anyone is confused (like me). I linked to Ming Cai & Jianhua Lu (2007) via stoat and realclimate. The realclimate post was about Graverson but the relevant comment was about Ming Cai & Jianhua Lu (2007).


The new paper in Nature GeoScience is Pithan/Mauritsen paper which looks at CMIP5 models.

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #90 on: February 05, 2014, 07:42:43 PM »
Crandles,

Sorry, the Stoat blog post links to this article:
http://www.nature.com/nature/journal/v451/n7174/full/nature06502.html
Which is about the Graverson paper.

You didn't link to the Nature blog post.

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #91 on: March 23, 2014, 10:03:27 AM »
For completeness. I've finally got round to blogging on the cause of the sea ice volume loss, here.
http://dosbat.blogspot.co.uk/2014/03/what-caused-volume-loss-in-piomas.html

Tor Bejnar

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Re: What is the cause of the PIOMAS volume loss?
« Reply #92 on: March 24, 2014, 04:20:51 AM »
I understand that precipitation (presumably mostly as snow) is increasing over the Arctic Ocean.  I understand snow reflects heat better than does ice (therefore summer melt is slowed) and snow insulates the ice underneath (therefore ice growth in winter is slowed).  As I verbally map the effects, more snow would put a damper on both melt and freeze.  I appreciate the thermodynamic wizardry some of you possess.  Is this inconsequential to the discussion of winter processes vs summer processes (or even not accurate)? 

Arctic ice is healthy for children and other living things.

Frivolousz21

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Re: What is the cause of the PIOMAS volume loss?
« Reply #93 on: March 24, 2014, 07:32:41 AM »
I understand that precipitation (presumably mostly as snow) is increasing over the Arctic Ocean.  I understand snow reflects heat better than does ice (therefore summer melt is slowed) and snow insulates the ice underneath (therefore ice growth in winter is slowed).  As I verbally map the effects, more snow would put a damper on both melt and freeze.  I appreciate the thermodynamic wizardry some of you possess.  Is this inconsequential to the discussion of winter processes vs summer processes (or even not accurate)?

more snow would allow for larger and deeper melt ponds though.
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Re: What is the cause of the PIOMAS volume loss?
« Reply #94 on: March 24, 2014, 02:46:43 PM »
Zhang and Rothrock have done a paper in 2005 covering the period 1948 to 1999, pdf here. In a nutshell; during that early period they find that the volume loss is due to loss of thinner mechanically undeformed ice, in other words - thinning of younger ice.

Such a thinning has continued into the PIOMAS record for this century, but most of the volume loss this century has come from the central Arctic and loss of thick, mechanically deformed multi year ice. I can provide graphics if needed, but for now I want to crack on.

So what's been happening to cause volume loss in PIOMAS last century is different from after 1995, when the large rapid drop in volume happened, in short Zhang and Rothrock 2005 is of no use because the mechanism has changed. It's possible that some of the other gridded data from PIOMAS might be able to help, but I'm trying to see if there's a quick and easy way to the answer before I a) ask Dr Zhang, b) try a more advanced approach using the other gridded PIOMAS data.

I can break the year into two discrete periods with their own processes going on, again I can go into why this is valid, but want to crack on with this train of thought. So I have the melt season and the freeze season. Being able to tie the loss to either would be advantageous as I could bring other research to bear in the search for the cause of the volume loss. (I have been playing around with this since before Christmas!)

Using PIOMAS monthly averages calculated from their main season I use April to September as the melt season, September to April as the freeze season, with both seasons stated for the year in which April falls. This gives me a series of numbers for volume gain and volume loss.

Year   Freeze   Melt
1980   15.334   15.925
1981   14.431   17.937
1982   16.165   15.468
1983   16.887   15.195
1984   15.137   15.705
1985   16.244   16.294
1986   16.359   14.863
1987   15.721   16.440
1988   15.842   16.214
1989   15.128   15.347
1990   15.139   16.090
1991   16.930   17.153
1992   16.056   14.565
1993   15.348   17.985
1994   17.292   15.877
1995   14.578   17.208
1996   16.220   13.495
1997   15.416   16.146
1998   16.188   17.795
1999   16.834   17.414
2000   16.117   16.074
2001   16.554   15.367
2002   15.159   16.587
2003   16.401   16.963
2004   15.473   15.716
2005   16.012   16.772
2006   15.830   16.002
2007   14.656   17.236
2008   18.468   17.750
2009   17.717   17.986
2010   16.267   18.658
2011   17.188   17.564
2012   17.520   18.358
2013   18.309   16.637

Taking these as zig zagging through the years the first month used is September 1979, the last September 2013, over that period there's been a volume loss of 11.866k km^3. If I sum the above columns I get: 548.920 and 560.786, subtract those numbers and the result is -11.866, no surprise there, the total loss is as a result of an imbalance between volume gains over autumn/winter and losses over the spring/summer.

The problem is I don't know whether freeze season volume gains are less than they 'should' be, melt season losses greater than they 'should' be, or a combination of those two factors.

I make up two synthetic series of volume loss, one using a melt season that is losing 0.5k km^3 per year more than the freeze season gains, the other with a freeze season that produces 0.5k km^3 less ice than is lost in the melt season. This illustrates the two exclusive possibilities, loss of volume due to freeze season processes, and loss of volume due to melt season processes.

Say I fix the nominal freeze and melt season to be 15k km^3, so without an offset the peak volume stays at the initial value, which I could set to 30k km^3. When I apply the 0.5k km^3 offset to either the melt or freeze season I get the same result, the melt season losses are larger than the freeze season gains, either because I've set the melt season to be 0.5k km^3 larger, or the freeze season to be 0.5k km^3 smaller. The point is that the observation that total melt season losses exceed total freeze season gains, by the amount of volume lost, does not tell us whether the losses have been from the melt season, freeze season or indeed both.

Anyone got any ideas as to how I might seperate out the relative roles of melt and freeze seasons? Or indeed is it likely to be impossible?

In the Zhang Rothrock paper I linked to above they say that losses may be from either melt or freeze season processes, suggesting they've not been able to determine which - or perhaps just didn't have the time to do the extra digging into the far more detailed data they had...

What happens if you first exclude the volume outside the Arctic Ocean proper? Seems an obvious thing to try, since the outside areas have always been seasonal and have very little impact on the minimum. Try calculating volume for only the region that was typically covered by ice in September in the 20th century.

ChrisReynolds

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Re: What is the cause of the PIOMAS volume loss?
« Reply #95 on: March 24, 2014, 08:25:35 PM »
Nightvid,

That's easily worked out from the regional piomas breakdowns I've previously worked out. Data is here:
http://dosbat.blogspot.co.uk/2013/12/regional-piomas-volume-data.html

But the Lindsay & Zhang paper ended up giving the answer I wanted, see also the point Ktonine was making at the end of the last page and top of this page.

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Re: What is the cause of the PIOMAS volume loss?
« Reply #96 on: March 24, 2014, 08:27:51 PM »
I understand that precipitation (presumably mostly as snow) is increasing over the Arctic Ocean.  I understand snow reflects heat better than does ice (therefore summer melt is slowed) and snow insulates the ice underneath (therefore ice growth in winter is slowed).  As I verbally map the effects, more snow would put a damper on both melt and freeze.  I appreciate the thermodynamic wizardry some of you possess.  Is this inconsequential to the discussion of winter processes vs summer processes (or even not accurate)?

Since 2007 the annual range of area/extent has increased, and since 2010 there have been unusually aggressive spring melts. Both of those are connected with a drop in ice thickness. So I think ice processes are beating snow.