During the melting season I'm regularly writing updates on the current sea ice extent (SIE) as reported by IJIS (a joint effort of the International Arctic Research Center and the Japan Aerospace Exploration Agency) and compare it to the sea ice extents in the period 2005-2010. NSIDC has a good explanation of what sea ice extent is in their FAQ. I also look at other things like sea ice area, concentration, volume, temperature and weather forecasts, anything that can be of particular interest. Check out the Arctic sea ice graphs webpage for daily updated graphs, maps and live webcam images.
September 24th 2011
This is the last SIE update for this melting season, which ended about two weeks ago (feels like an eternity). I have basically said everything I think needed saying with regards to the minimum, so I won't repeat myself here. Just like last year I've had a very educative experience, and I'd like to thank the 'old' crew and newcomers for all the info and inspiring speculation they've been bringing to this little corner of the Internet. That's what's making this blog worthwhile in my opinion.
As always I'll start with the IJIS sea ice extent graph:
We can see the upswing when the melting season ended abruptly on September 9th. After a few days the increase slowed down and it's now more or less tracking 2008. The interesting thing to do is to try and find out what the mechanism is behind the uptick and the subsequent slowdown in increase.
It has obviously everything to do with the weather at this stage of the transition phase between melting/compacting and spreading/freezing, so I suggest we first have a look at this animation of images from the DMI Centre for Ocean and Ice that I've saved:
Around the 8th we can see the start of what I warned would bring the melting season to an early end: a big low in the middle of the Arctic Ocean. After that it's clear that the exact opposite of an Arctic Dipole Anomaly set-up basically made sure we wouldn't be seeing any serious double dip, like we did last year when a late high over the Canadian Archipelago extended the melting season and caused a slightly lower minimum than was called a week earlier.
To tell the truth, in the past week I haven't been looking at the ice as intently as the preceding 4-5 months. But a couple of days ago I posted a comment describing what I think has happened since the minimum:
The large and quick uptick that ended the melting season, was mainly caused by the openings between the ice floes in the Arm of weak ice in the East Siberian Sea refreezing (and having snow dropped on them). It has filled up a lot as we can see on the various sea ice concentration maps.
As there is not much more to fill up, and the waters around much of the Arctic are too warm to freeze up right now (despite a first smallish uptick on the DMI 80N temperature chart), wind patterns are now compacting the ice pack here and there (Beaufort and Greenland Seas). Hence the drop in IJIS SIE and the leveling off of all the other graphs.
Here's an animation of the Uni Bremen sea ice concentration maps from the 9th and 23rd of September:
The huge area of low concentration ice on the Pacific side of the Arctic, from the Beaufort Sea to the Laptev Sea, has filled up. All the weak ice in the Arm in the East Siberian Sea was saved, like it was last year. Furthermore the big low in the middle of the Arctic Ocean pushed the edge of the ice pack outwards, with leads behind it getting frozen and/or snowed over.
One side effect of this is that the edge on the other side of the pack is exactly the same as it was two weeks ago. Both the Northwest Passage and the North Sea Route still look very open (although there probably is some refreezing going on there not showing up yet on the sea ice concentration maps) and the channels between the islands of the Canadian Archipelago are finally filling up. I'm not really sure if that's because of refreezing (which means we have first year ice there next year which could melt out even faster than the ice in the CA did this year), or if those lows pushed in some thick ice from the Arctic Basin after all.
When the atmosphere gets cold enough, the Arctic waters have the opportunity to release their heat so that the top layer can start to freeze. So, one thing I always look out for with regards to refreezing are upticks on the DMI mean temperature above 80N graph:
There has been one uptick so far, with temps going down real low, probably because of that low pressure area in the middle of the North Pole. I expect to see another uptick when the warm waters at the edges start to release their heat for real. In fact, it looks like it could have just started. It's pretty warm - relatively speaking of course - in the Arctic right now, which probably is a combination of heat release and atmospheric patterns. Incidentally or not, there is finally some blue to be seen near the South Pole, which had been flaming red almost all SH winter:
The melting season is over (there, that's the last time I said it), but there'll be less hibernation this winter. I want to keep my eyes open and see if we have another weird winter season on the Northern Hemisphere, like we had in 2009 and 2010. If we do, I want to know if there's any connection with our beloved Arctic.
I'm also planning on writing about one post a month on interesting scientific papers and things that pop up (hopefully some more news from CryoSat-2). And there'll be Open Threads, of course.
Thanks again for another great melting season. 2012, here we come!
PS Bill Fraser has a comment up to inform us that he posted a petition to the US White House, demanding a tax on externalities. I'd sign it if I were a US citizen, but alas. So I'm calling on all Americanos here to sign it (whether you agree with it or not ;-) ).
PPS Just like last year, I'll end with a song: