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Artful Dodger

Nice resource, Nevin. You've got friends in *cold* places... (pardon my Garth Brooks)

Andrew Xnn

My understanding (and please somebody correct me if I err) is that these systems measure the difference in time it takes radar signals to bounce off the surface of the ice compared to the cracks between the ice. From this, they can deduce how thick the ice is above the water and then in turn calculate how thick the ice is on average.

What hasn't been stated is if they are both looking at the same data and coming up with different answers or if they have different satellite sources.

I'll guess that they are looking at the same data and are coming up with different answers because there is more than 1 way to interpret the data.

For example, while the thickness of the ice obviously varies, the amount of open water between ice varies as well. In addition, melt ponds must be tricky to deal with since they may appear to be open water between ice. Of course melt ponds are summer thing. So, we also have the problem that in some seasons the same data could mean different things.

Finally, last year Sept one of the systems came up with 4000km^3 of ice with a long term trend of losing between 350 to 1000km^3/year. Not sure if the other system had similar findings or not.

Anyhow, many many thanks Neven. Great job and also to all the knowledgeable com mentors out there in cyber land.

L. Hamilton

When I was looking at PIOMAS volume estimates for my guest post earlier this month, I checked out the relationship between PIOMAS September volume and NSIDC area. Not surprisingly, there's a fairly strong linear relationship (r = .94). Here's how they moved together:

http://img.photobucket.com/albums/v224/Chiloe/Climate/Volume_area_2.png

L. Hamilton

Step-back view, same data but with zero points shown for perspective:

http://img.photobucket.com/albums/v224/Chiloe/Climate/Volume_area_1.png

MikeAinOz

Neven it's good to you you covering ice volume. How data is collected for these models is interesting. They are based on ensemble data, with radar playing a very limited role at the moment. Most data comes from floats and other on-site mearurement. Here's a paper about TOPAZ data http://www.cawcr.gov.au/staff/pxs/wmoda5/Oral/Bertino_Sakov.pdf
, it's a little old but covers the subject nicely.

Neven

Thanks a lot for that PDF, MikeAinOz. Not too much text, not too complex, just the way I like it. ;-)

BTW, I forgot to properly attribute the picture at the top of the post. I snitched it from the ESA blog.

R. Gates

The differences in the models is very interesting to look at and you've done a great job at highlighting them. I do have very strong confidence that in a few years hence, because of CrySat 2 and eventually Icesat 2, that the models will begin to become both more refined, and then less important as it is replaced by real verified data on thickness. Within a few years we should be getting regular sea ice volume data that will provide a whole new way of considering the state of the arctic cryosphere. I'm suspecting the AGW skeptics will be rather quiet by then...

Peter Ellis

R. Gates: Provably wrong, I'm afraid.

Either current volume models like PIOMAS are wrong about the amount remaining and the rate of decline, or they're right.

If they're wrong - for example there's more there than expected, or the decline is slower - then the skeptics will be noisily cock-a hoop.

If they're right, them we won't be getting regular summer sea ice volume data in a few years' time, because there will be no summer sea ice.

:-(

R. Gates

Peter,

I think we'll find that PIOMAS is probably better than the others, but still off the mark a bit. Eventually CryoSat 2 and then IceSat 2 will minimize the need for these models as we'll have actual data. And as far as summer sea ice goes, we've definitely got a quite a few summers before we'll see an ice free Arctic (my guess is at least 15 or so) and it could very well be that it will linger as virtually ice-free in summer (less than 1 million sq. km.)for many years with small pockets clinging north of Greenland and/or the Canadian Archipelago. And of course, it will always freeze over again in winter to one degree or another, and so CryoSat 2 will be useful to monitor rates of thickness growth, etc.

Kevin McKinney

"And of course, it will always freeze over again in winter to one degree or another, and so CryoSat 2 will be useful to monitor rates of thickness growth, etc."

Not necessarily. Modeling work has shown that consistently ice-free summers will likely be enough to 'flip' the Arctic into a year-round ice-free state. That's not a definitive result, if I understand it correctly, but is a very real (and very unsettling) possibility. I don't have the details at hand--and don't have time just now for a search--but I'm sure one of the regulars can oblige.

R. Gates

Kevin,

Certain models indicate rather interesting behavior for the ice even after an ice free summer. This study for example:

http://www.agu.org/pubs/crossref/2011/2010GL045698.shtml

Shows that an ice free summer may in fact allow greater amounts of heat to escape during the fall and winter from the open arctic water. Leading to cooler water and ice formation.

What I'm getting at is that the ice may have some interesting behavior as we get near or at an ice free summer arctic, showing both positive and negative feedbacks effects in unexpected combinations as any chaotic system does when undergoing change.

This will all of course play havoc with the weather here at the lower latitudes, especially in the winter.

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