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Author Topic: Latest PIOMAS update (November 2019)  (Read 1060380 times)

Wipneus

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Re: Latest PIOMAS update (February)
« Reply #800 on: February 04, 2016, 12:32:30 PM »
Animation of the daily ice thickness for January.

Click to start the 3 Meg animation.

[EDIT: showed the wrong year, this should be 2016]
« Last Edit: May 29, 2016, 03:26:22 PM by Wipneus »

Jim Hunt

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Re: Latest PIOMAS update (February)
« Reply #801 on: February 04, 2016, 01:42:26 PM »
Click to start the 3 Meg animation.

I click, but I don't see any animation :( Firefox on Scientific Linux and Chrome on Windows 7.
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Wipneus

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Re: Latest PIOMAS update (February)
« Reply #802 on: February 04, 2016, 03:00:36 PM »
Click to start the 3 Meg animation.

I click, but I don't see any animation :( Firefox on Scientific Linux and Chrome on Windows 7.

It is the forum software that does not upload any of the frames but the first one, if it is in that mood.

So when I upload an animated gif, I always try to remember to check if it works, if not fiddle with the file and try again and repeat.

This time, being rather busy with replacing the Raspberry Pie's harddrive (1TB->3TB), I just forgot.

Loading and saving in the Gimp was enough to convince the forum software that the animation was OK.

Jim Hunt

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Re: Latest PIOMAS update (February)
« Reply #803 on: February 04, 2016, 03:07:17 PM »
Loading and saving in the Gimp was enough to convince the forum software that the animation was OK.

Thanks Wipneus. OK for me now!
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TenneyNaumer

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Re: Latest PIOMAS update (February)
« Reply #804 on: February 04, 2016, 05:37:22 PM »
PIOMAS is hopelessly wrong.

The sea ice is right now undergoing its breakup pattern, normally seen in late March ("normal" in the last few years; pre-2007 it was in May-June).

The ice is so thin that the normal currents are breaking it up.  (Not to mention that the ice has been beaten to death by storms entering the Arctic all winter long.)

You can watch it here:  https://weather.gc.ca/data/satellite/hrpt_dfo_ir_100.jpg

seaicesailor

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Re: Latest PIOMAS update (February)
« Reply #805 on: February 04, 2016, 05:43:02 PM »
With this indication, and the current high if it persists, there will be another interesting Beaufort battle this year

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Re: Latest PIOMAS update (February)
« Reply #806 on: February 04, 2016, 06:10:02 PM »
PIOMAS is hopelessly wrong.

The sea ice is right now undergoing its breakup pattern, normally seen in late March ("normal" in the last few years; pre-2007 it was in May-June).

The ice is so thin that the normal currents are breaking it up.  (Not to mention that the ice has been beaten to death by storms entering the Arctic all winter long.)

Caution!  Remember all the fuss about the 'Crackocalypse' in 2013.  It ended up meaning extra MYI got advected into the Beaufort Sea, which helped stall the melt there in summer of 2013.  Meanwhile, the open leads vented heat to the atmosphere and rapidly froze over, so the net effect probably increased ice production.

Not all ice fracturing is equivalent (remember that as ice cools, it shrinks, which will also cause cracks to open), and open leads in the coldest part of winter is a great way for the Arctic to lose heat.

I would be very wary of making any projections about the melt season until ooh, mid-May or thereabouts.

jdallen

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Re: Latest PIOMAS update (February)
« Reply #807 on: February 04, 2016, 06:11:28 PM »
PIOMAS is hopelessly wrong.

The sea ice is right now undergoing its breakup pattern, normally seen in late March ("normal" in the last few years; pre-2007 it was in May-June).

The ice is so thin that the normal currents are breaking it up.  (Not to mention that the ice has been beaten to death by storms entering the Arctic all winter long.)

You can watch it here:  https://weather.gc.ca/data/satellite/hrpt_dfo_ir_100.jpg

I like the CWS microwave and IR satellite imagery.  It was looking at that which brought me to the page years ago.  What I'm seeing now looks quite familiar - a major cracking event in the Beaufort - not unakin to what we saw over each of the last few years.

Do others recall timing?  I think its about the same timing this year, maybe a week or two earlier?
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Peter Ellis

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Re: Latest PIOMAS update (February)
« Reply #808 on: February 04, 2016, 06:25:32 PM »
It's maybe a week earlier than 2013.  I suspect this kind of event may be one of the feedbacks that stabilises winter ice volume loss - i.e. thinner ice is more likely to fracture into leads, thereby exposing more water for rapid ice formation.  I have certainly seen publications that say increase ridging of thinner ice is such a feedback, and ridging and rifting are logically part of the same phenomenon of fracture and regrowth.

Remember that there is no melt - no volume loss - in the Beaufort at the moment, nor will be for months yet.  If you see a gap open up, then the ice that used to be in that gap is now somewhere else, making another part of the ice sheet thicker.

Wipneus

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Re: Latest PIOMAS update (February)
« Reply #809 on: February 04, 2016, 06:34:51 PM »
Here is a side by side animation of the last two weeks now in 2016 compared with 2013 as seen by AMSR2 (ASI sea ice concentration data from UH Hamburg).
The "Crackocalypse" did not happen until 20 February or so.

(click req'd)

jdallen

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Re: Latest PIOMAS update (February)
« Reply #810 on: February 04, 2016, 06:52:22 PM »
Here is a side by side animation of the last two weeks now in 2016 compared with 2013 as seen by AMSR2 (ASI sea ice concentration data from UH Hamburg).
The "Crackocalypse" did not happen until 20 February or so.

(click req'd)
Two and a half weeks? That may actually be significant.
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Peter Ellis

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Re: Latest PIOMAS update (February)
« Reply #811 on: February 04, 2016, 07:21:55 PM »
... means even longer for the exposed water to freeze over and thicken. We really mustn't leap to assuming every event is a harbinger of the end.

jdallen

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Re: Latest PIOMAS update (February)
« Reply #812 on: February 04, 2016, 08:38:41 PM »
... means even longer for the exposed water to freeze over and thicken. We really mustn't leap to assuming every event is a harbinger of the end.
Absolutely and I understand your caution, Peter.

I would be happier if the air temps were 5-10C cooler so we could catch up a bit.

I'm curious what the additional contribution to heat loss open leads would add.  I'm wondering if it would even be as much as a couple of percent - they don't really cover that much area, even when considered in aggregate over time.

I'm looking at the cracking as a qualitative signal reflecting other dimensions of the system over all.  I doubt it will have a significant causative effect on the melt season - save for how it shuffles MYI around.
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jdallen

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Re: Latest PIOMAS update (February)
« Reply #813 on: February 04, 2016, 10:36:37 PM »
Pertinent to discussion about freezing and thickening, this is what we're going to start struggling with soon now, especially in the peripheral seas.

Sunrise.

The Bering and Okhostk are already getting multiple hours of sunlight a day over mostly open water.  If they aren't getting sunlight, the clouds will be holding in heat.  It will be rapidly ramping up in the Chukchi.

The Kara which has had very thin coverage (particularly the Western) over just a few weeks, will be back in daylight  in a few days, as will the Barents, which has been supernaturally warm all winter. 

Even with the high pressure, most of the basin is maintaining temperatures of 5C or more above normal.

Combine that with even modest returning insolation (especially where it's over open water) and we are rapidly running out of places where we can add significant volume.
« Last Edit: February 04, 2016, 10:43:55 PM by jdallen »
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TenneyNaumer

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Re: Latest PIOMAS update (February)
« Reply #814 on: February 05, 2016, 05:29:07 AM »
I have been downloading these satellite photos since early 2007 (unfortunately, I did not backup the old laptop most of them were on -- now I keep them on a USB drive).  That's 9 years of peering at these images.   In 2007, the ice only barely began to break up at the end of May, and by breakup, I mean that a crack appeared along the edge of the entire Canadian archipelago.  The ice was incredibly thick compared to what we have now.  Recall that land-fast ice shelves existed, some 120-feet thick.  Those all broke away and disappeared in the years after 2007.  Some of these ice shelves covered areas that had not seen open water in 14,000 years.  Those ice shelves had acted as a sort of break on the movement of the sea ice.  Further, although an increasing number of storms were entering the Arctic, during the winter months, this was still a rare occurrence.  Not anymore.

And you have only to look at the speed of the sea ice.  By about 2009, the speed had doubled over the long-term average.  Lord only knows how fast it is moving these days compared to the 1980s, for example. 

Further, the entire character of the sea ice is radically different -- you might as well be discussing the difference between cucumbers and artichokes.  In the past, the ice was very dense and strong, now it is like Swiss cheese made of spongy slush.

Here are some satellite photos from other years (2012 and 2013) at this time:











jdallen

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Re: Latest PIOMAS update (February)
« Reply #815 on: February 05, 2016, 09:42:00 AM »
I have been downloading these satellite photos since early 2007... <snippage>

All in all, not qualitatively that much different than what we are seeing now, from what I can tell.

Best guess is, 2016 is acting in accordance with what has been typical since 2010.
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Jim Hunt

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Re: Latest PIOMAS update (February)
« Reply #816 on: February 05, 2016, 01:44:36 PM »
Further, the entire character of the sea ice is radically different -- you might as well be discussing the difference between cucumbers and artichokes.  In the past, the ice was very dense and strong, now it is like Swiss cheese made of spongy slush.

Here are some of my own satellite screenshots:

http://GreatWhiteCon.info/resources/arctic-sea-ice-images/

Have you by any chance read Chris Reynolds on this topic, so dear to all our hearts?

http://forum.arctic-sea-ice.net/index.php/topic,933.0.html

How about this paper, mentioned in the latest edition of Arctic Sea Ice News?

"Predicted slowdown in the rate of Atlantic sea ice loss"
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Neven

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Re: Latest PIOMAS update (February)
« Reply #817 on: February 05, 2016, 09:17:18 PM »
I'm struck by the difference between 2016 and 2015, with all that deep blue north of Greenland and the CAA:
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jdallen

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Re: Latest PIOMAS update (February)
« Reply #818 on: February 05, 2016, 10:06:54 PM »
I'm struck by the difference between 2016 and 2015, with all that deep blue north of Greenland and the CAA:
Yeah, that's worrisome.  I think it exemplifies the odd movement of the ice at the end of the last melt season, and the generally unseasonably warm temperatures we've seen over the last 6 weeks.
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Re: Latest PIOMAS update (February)
« Reply #819 on: February 05, 2016, 10:40:29 PM »
... means even longer for the exposed water to freeze over and thicken. We really mustn't leap to assuming every event is a harbinger of the end.

Last year I got the strong impression that much of the ice which papered over the crackopalypse in Feb/Mar didn't last too long into the melting season (it is zeroth year ice, after all). Assuming for a moment that I'm right about that, the net effect of the cracking on the season as a whole isn't clear, to me at least, at all.

Yes, the open water in Feb causes faster ice formation now, but if those same areas become open water again when the sun is high, wouldn't they prematurely lower the average surface albedo, causing faster melting later?

On balance, while the net effect on the season doesn't appear obvious, it would seem reasonable to suppose that the earlier in the season the crackup happens, the less likely it is to result in a net decrease in volume - since the paper over the cracks would be thicker and take longer to melt...

Shared Humanity

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Re: Latest PIOMAS update (February)
« Reply #820 on: February 06, 2016, 02:08:13 AM »
I'm struck by the difference between 2016 and 2015, with all that deep blue north of Greenland and the CAA:

CAA took a beating last melt season. Unless thick MYI moves in, isn't this what we would expect to see?

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Re: Latest PIOMAS update (February)
« Reply #821 on: February 06, 2016, 12:13:57 PM »
I'm struck by the difference between 2016 and 2015, with all that deep blue north of Greenland and the CAA:

CAA took a beating last melt season. Unless thick MYI moves in, isn't this what we would expect to see?

All that deep blue seems noteworthy in part because they are red in maps showing comparison with other years mainly 2010 through 2014. If this year was particularly thin you would expect to see blue in these area against all or at least most year. This therefore seems to point to January 2015 being particularly thick in those areas.

So conclusion seems to be ice in those area in 2016 is thicker than 2010 through 2014 but not as thick as in 2015 when it was particularly thick in those areas.

That doesn't seem hugely exciting. Atlantic edge looks thin compared to most years, very nearly as thin as 2013 when it was vulnerable/still recovering from 2012. This seem to me to be the more interesting conclusion to reach.

A less exciting observation might be the ice is thicker over large areas compared to 2011, 12, 13, and 14.

Another point being this is January average and if the volume is only increasing very slowly part of this effect is not yet showing through.

magnamentis

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Re: Latest PIOMAS update (February)
« Reply #822 on: February 06, 2016, 01:01:00 PM »
I'm struck by the difference between 2016 and 2015, with all that deep blue north of Greenland and the CAA:

CAA took a beating last melt season. Unless thick MYI moves in, isn't this what we would expect to see?

All that deep blue seems noteworthy in part because they are red in maps showing comparison with other years mainly 2010 through 2014. If this year was particularly thin you would expect to see blue in these area against all or at least most year. This therefore seems to point to January 2015 being particularly thick in those areas.

So conclusion seems to be ice in those area in 2016 is thicker than 2010 through 2014 but not as thick as in 2015 when it was particularly thick in those areas.

That doesn't seem hugely exciting. Atlantic edge looks thin compared to most years, very nearly as thin as 2013 when it was vulnerable/still recovering from 2012. This seem to me to be the more interesting conclusion to reach.

A less exciting observation might be the ice is thicker over large areas compared to 2011, 12, 13, and 14.

Another point being this is January average and if the volume is only increasing very slowly part of this effect is not yet showing through.

honestly speaking i take all sea-ice-volume images with a prise of salt. going through the various available graphics they show far too different results to appear reliable. might well be the one of them is correct but who knows which one. especially many of those graphics don't correspond with what we see with our own eyes. last summer some of them were showing thick ice where satellites showed open water and polnyas LOL

Wipneus

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Re: Latest PIOMAS update (February)
« Reply #823 on: February 06, 2016, 01:55:15 PM »
Regular PIOMAS volume data update is still pending.
Calculating those from the gridded data I get for January:

Quote
2016 1 15.742
2016 2 15.829
2016 3 15.93
2016 4 16.013
2016 5 16.109
2016 6 16.193
2016 7 16.295
2016 8 16.409
2016 9 16.536
2016 10 16.685
2016 11 16.82
2016 12 16.917
2016 13 17.018
2016 14 17.116
2016 15 17.232
2016 16 17.315
2016 17 17.394
2016 18 17.482
2016 19 17.579
2016 20 17.668
2016 21 17.766
2016 22 17.87
2016 23 17.978
2016 24 18.073
2016 25 18.148
2016 26 18.206
2016 27 18.246
2016 28 18.315
2016 29 18.393
2016 30 18.471
2016 31 18.538

Attached are the preliminary volume and volume anomaly graphs. No surprise, January growth was relatively slow.

TenneyNaumer

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Re: Latest PIOMAS update (February)
« Reply #824 on: February 06, 2016, 11:15:12 PM »
Very sorry I don't have images from earlier years -- the qualitative difference is quite stark. 

Wipneus's second graph at Reply 823 is very telling.  PIOMAS would have you believe the ice volume in Nov 2014 was as high as in 2008.  This defies credulity.  We know the ice has changed fundamentally since 2008.

I have been downloading these satellite photos since early 2007... <snippage>

All in all, not qualitatively that much different than what we are seeing now, from what I can tell.

Best guess is, 2016 is acting in accordance with what has been typical since 2010.

Peter Ellis

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Re: Latest PIOMAS update (February)
« Reply #825 on: February 07, 2016, 05:22:04 PM »
I'm curious what the additional contribution to heat loss open leads would add.  I'm wondering if it would even be as much as a couple of percent - they don't really cover that much area, even when considered in aggregate over time.

Much more than you'd think. Consider this graph.



This shows the rate of ice growth in cm per day dependent on the current thickness of the ice. Ice formation (equivalent to energy loss via the enthalpy of freezing) in an open lead is around 30x as high as the energy loss through typical 1st year ice at this time of year (i.e. 1-1.5m thick).

If there are no leads before the cracking event, and this increases to 3% open water area after the cracking event, then the total heat loss goes from 100 (arbitrary units) to 187, i.e. it almost doubles the total rate of ice volume formation. This increased ice formation rate then slowly decays back to normal over the next couple of weeks as the leads seal over.

TenneyNaumer

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Re: Latest PIOMAS update (February)
« Reply #826 on: February 07, 2016, 07:51:07 PM »
Wouldn't the graph assume certain conditions as, for example, the air temperature above the ice and the water temperature below it?  Possibly it assumes that the temperature of the water is at the freezing point.  What if the water's temperature is actually one or two degrees higher?

The breakup pattern of leads is continuing:

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Re: Latest PIOMAS update (February)
« Reply #827 on: February 07, 2016, 08:01:32 PM »
Wouldn't the graph assume certain conditions as, for example, the air temperature above the ice and the water temperature below it?
The fundamental equation stays the same even if the parameters change, so the shape of the graph stays the same.  The shape is determined by the insulating properties of ice.

Simply put, heat flow through a few-cm thick layer of nascent ice will be many fold less than the heat flow through a 1.5-metre layer of mature FYI. Colder air will change the scale of the y axis, but not change the ratio between thin/thicker ice growth rates.

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Re: Latest PIOMAS update (February)
« Reply #828 on: February 07, 2016, 08:08:38 PM »
I'm curious what the additional contribution to heat loss open leads would add.  I'm wondering if it would even be as much as a couple of percent - they don't really cover that much area, even when considered in aggregate over time.

Much more than you'd think...

[...]

This shows the rate of ice growth in cm per day dependent on the current thickness of the ice. Ice formation (equivalent to energy loss via the enthalpy of freezing) in an open lead is around 30x as high as the energy loss through typical 1st year ice at this time of year (i.e. 1-1.5m thick).

If there are no leads before the cracking event, and this increases to 3% open water area after the cracking event, then the total heat loss goes from 100 (arbitrary units) to 187, i.e. it almost doubles the total rate of ice volume formation. This increased ice formation rate then slowly decays back to normal over the next couple of weeks as the leads seal over.

The area being refrozen is significant. People expected in 2013 the cracks be very vulnerable, even foster positive feedback on the melting, because the new ice is thinner, easier to melt, it has less snow on top, and once melt, its albedo drops helping later melt of older ice.
Maybe we did not see all that in 2013 because weather during that melting season was cold, there was no spark.

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Re: Latest PIOMAS update (February)
« Reply #829 on: February 08, 2016, 08:13:50 PM »
Wouldn't the graph assume certain conditions as, for example, the air temperature above the ice and the water temperature below it?  Possibly it assumes that the temperature of the water is at the freezing point.  What if the water's temperature is actually one or two degrees higher?
...
The water temperature below the ice can only be at freezing point unless the ice is melting and there is heat input into the water (e.g. sunshine). At present freezing point temperature is a very good assumption.
The graph shows the difference ice thickness makes to growth rate at otherwise equal conditions, if the discussion is does cracking increase ice production or not it is the right graph to look at.
What happens later in the season to melting rates is more complex. Draining of meltponds is favoured by cracked floes, late ice gets less snow fall but form watching observation buoys I would say snow is loose and drifting so it doesn't stay where it has fallen. Not an obvious answer on what has the stronger effect.

johnm33

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Re: Latest PIOMAS update (February)
« Reply #830 on: February 08, 2016, 09:51:40 PM »
The sea surface temperature shows anomolies over wide areas, presumably through the cracks

this shows an anomoly of .5C so -1.3C and above freezing[-1.8] wayne of http://eh2r.blogspot.ca/
a frequent commenter on the ASI blog, and a keen observer of the ice has stated a few times that you need an air temp. of -11C to get sea water to freeze, so where the graph says winter one assumes temperarures below that. Despite frequent air temp. anomolies of +15C or more I'm not sure it's gone above -11C in Beaufort at all. If you check out waynes blog he has a post up about his doubts on Piomas. If the sst anomolies persist then I doubt we'll get a 'normal' refreeze in Piomas's terms.
http://earth.nullschool.net/#current/ocean/surface/currents/overlay=sea_surface_temp_anomaly/orthographic=-14.55,108.73,1106/loc=-132.129,70.653

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Re: Latest PIOMAS update (February)
« Reply #831 on: February 10, 2016, 03:43:58 PM »
PSC has now updated their PIOMAS  daily volume data as well. I updated my graphics, see the top post

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Re: Latest PIOMAS update (February)
« Reply #832 on: February 10, 2016, 04:15:57 PM »
PIOMAS February 2016 is out on the ASIB. Big, big changes that Wipneus was already alluding to!
« Last Edit: February 10, 2016, 06:14:37 PM by Neven »
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Re: Latest PIOMAS update (February)
« Reply #833 on: February 10, 2016, 07:22:18 PM »
PIOMAS February 2016 is out on the ASIB. Big, big changes that Wipneus was already alluding to!
Knew all this heat was going to have a dramatic effect on thickness.  Gratifying for my conclusion to be quantified and affirmed.  Terrifying that I was right.
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Re: Latest PIOMAS update (February)
« Reply #834 on: March 09, 2016, 12:58:23 PM »
PIOMAS has been updated. February saw the second lowest February increase in the 2007-2016 record, meaning 2016 is now lower than 2012 and every other year, just behind 2011. I'll have a ASIB post on this later today.
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Re: Latest PIOMAS update (March)
« Reply #835 on: March 09, 2016, 03:51:26 PM »
 Noob question but how accurate is the PIOMAS model? If you look at the picture the DMI (center) and HYCOM (right) models look totally inaccurate over the CAB when compared to the Cryosat measured data. It's not reassuring that if those models are inaccurate at high latitudes that PIOMAS is.
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Re: Latest PIOMAS update (March)
« Reply #836 on: March 09, 2016, 04:09:24 PM »
Yes, PSC has updated their PIOMAS  daily volume data. I updated my graphics, see the top post

Monthly gridded thickness data also updated , I will post the graphics here later.
Daily gridded data: not yet.

Neven

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Re: Latest PIOMAS update (March)
« Reply #837 on: March 09, 2016, 05:26:54 PM »
Noob question but how accurate is the PIOMAS model? If you look at the picture the DMI (center) and HYCOM (right) models look totally inaccurate over the CAB when compared to the Cryosat measured data. It's not reassuring that if those models are inaccurate at high latitudes that PIOMAS is.

Hi Trebuchet. First of all, CryoSat also has its problems and isn't perfect. Personally, I don't put much trust in the DMI and HYOM/ACNFS ice thickness distribution maps, but over the years I have to say that PIOMAS has always given a good feel of the general situation with regards to Arctic sea ice volume. Wipneus posts awesome distribution maps too, but I'm not sure how accurate these are either. But a diffcerence with other models is that observational data (thickness measurements by planes, subs, scientists on the ice) gets assimilated for the PIOMAS product.
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Re: Latest PIOMAS update (March)
« Reply #838 on: March 09, 2016, 09:57:43 PM »
Wow the overall thickening for last two months combined is so small. High temperature anomalies sustained surely had a lot to do with this. Direct AGW preconditioning.

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Re: Latest PIOMAS update (March)
« Reply #839 on: March 10, 2016, 12:05:52 AM »
Blog post is up: PIOMAS March 2016.
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Re: Latest PIOMAS update (March)
« Reply #840 on: March 10, 2016, 10:10:34 AM »
Average monthly thickness of February 2016 compared with years 2007-2015.

Click on the images for bigger pictures.

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Re: Latest PIOMAS update (March)
« Reply #841 on: March 10, 2016, 10:18:07 AM »
Animation of the daily ice thickness for February. Ice coming from the region north of Greenland can be seen exiting through the Fram Strait.

Click to start the 3 Meg animation.

[UPDATE: fixed the animation, it was showing 2015 ]
« Last Edit: April 05, 2016, 06:16:15 PM by Wipneus »

Richard Rathbone

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Re: Latest PIOMAS update (March)
« Reply #842 on: March 11, 2016, 03:10:27 PM »
Noob question but how accurate is the PIOMAS model? If you look at the picture the DMI (center) and HYCOM (right) models look totally inaccurate over the CAB when compared to the Cryosat measured data. It's not reassuring that if those models are inaccurate at high latitudes that PIOMAS is.

Hi Trebuchet. First of all, CryoSat also has its problems and isn't perfect. Personally, I don't put much trust in the DMI and HYOM/ACNFS ice thickness distribution maps, but over the years I have to say that PIOMAS has always given a good feel of the general situation with regards to Arctic sea ice volume. Wipneus posts awesome distribution maps too, but I'm not sure how accurate these are either. But a diffcerence with other models is that observational data (thickness measurements by planes, subs, scientists on the ice) gets assimilated for the PIOMAS product.

HYCOM/CICE models are different in a few respects from PIOMAS.

HYCOM/CICE is a forecast model, it predicts what the state of the Arctic will be tomorrow, based on what it thinks the state of the Arctic is today. PIOMAS is a hindcast model, it calculates what the state of the Arctic was last month based on measurements of what the state of the Arctic was last month. So where measurements are available, PIOMAS is likely to be more accurate. In particular, since PIOMAS uses reanalysed weather, while CICE uses weather predictions, PIOMAS should normally have a rather better idea of what the state of the weather was, and project ice conditions through the month better as a result. So if you want to know what the state of the Arctic was last month, PIOMAS should normally be the better guide. However, if you want to know what it will be tomorrow, CICE will make a guess and PIOMAS won't.

PIOMAS takes a lot more data into account than HYCOM/CICE does, and some of the assimilation in HYCOM/CICE models is problematic.

Both use measurements of ice concentration, but the only other data assimilated by HYCOM/CICE is sea surface temperature, and that's not a good thing to assimilate in areas with ice, because water in contact with ice is constrained to be at its melting point, so you don't actually gain anything by using data, and you can send the model haywire if you assimilate measurement inaccuracies too strongly (as was seen last year when a HYCOM/CICE model sent salinity all over the place to get the melting point of ice to match up with the data it was assimilating).

The ocean structure in HYCOM/CICE has to work for weather prediction as well as heat transfer to ice, while in PIOMAS it just has to work for heat transfer to ice. I think this is behind the tendency of HYCOM/CICE to have a shorter and more aggressive melt season that PIOMAS. CICE puts heat directly from insolation into melting the ice in July, while PIOMAS puts it into heating the ocean and continues bottom melting with that heat into September.

However neither are able to constrain thickness details at all closely from measurement, and both will have a lot of compensating errors (they'll get what proportion is a given thickness about right, but not where it is) and you shouldn't pay much attention to the thickness details as opposed to the broad picture.

HYCOM/CICE if you want to know what the ice will look like in 2 days time.
PIOMAS if you want to know what the total volume was last month.

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Re: Latest PIOMAS update (March)
« Reply #843 on: March 11, 2016, 11:21:22 PM »
Thanks, Richard. That's a great explanation.
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slow wing

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Re: Latest PIOMAS update (March)
« Reply #844 on: March 11, 2016, 11:44:05 PM »
Thanks, appreciated.


But is the Cryosat measured ice thickness data more accurate than all the models? That would be my starting assumption. If not, why not?

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Re: Latest PIOMAS update (March)
« Reply #845 on: March 12, 2016, 01:19:01 AM »
But is the Cryosat measured ice thickness data more accurate than all the models? That would be my starting assumption. If not, why not?

There's an entire thread devoted to the topic:

Piomas vs. CryoSat
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Re: Latest PIOMAS update (March)
« Reply #846 on: March 12, 2016, 12:32:01 PM »
Thanks, appreciated.


But is the Cryosat measured ice thickness data more accurate than all the models? That would be my starting assumption. If not, why not?

Short version - nobody really knows, because measuring ice thickness is really hard.  Or even defining ice thickness, come to that - average height of a rugged landscape is a slippery concept.

slow wing

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Re: Latest PIOMAS update (March)
« Reply #847 on: March 13, 2016, 01:10:34 AM »
Thanks for your replies and pointing to the relevant thread.

Yes, early in the thread has some discussion on the measurement difficulties associated with snow cover on the ice.


Concerning a definition of ice thickness, I would have thought solid water mass per unit area would be a useful definition to try to measure/model towards. (A reference ice density constant would convert the units to length/thickness.) To first order, that gives the amount of heat required to melt it out - up to second order corrections for snow vs. ice and ice salinity - which is what is mainly of interest to us.

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Re: Latest PIOMAS update (March)
« Reply #848 on: March 13, 2016, 05:26:36 PM »
Instead of focusing on models, you should be focusing on the actual sea ice.  It is not solid -- it is full of large holes like swiss cheese.  The ice now is nothing like it was in 2012. 

We've been getting plenty of information that it is soft like butter.  It used to be very solid and hard.

It is simply not the same animal. 

Andreas T

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Re: Latest PIOMAS update (March)
« Reply #849 on: March 13, 2016, 07:45:41 PM »
Instead of focusing on models, you should be focusing on the actual sea ice.  It is not solid -- it is full of large holes like swiss cheese.  The ice now is nothing like it was in 2012. 

We've been getting plenty of information that it is soft like butter.  It used to be very solid and hard.

It is simply not the same animal.
what do you expect to be inside those "swiss cheese holes"?