This post is a combination of several things. First of all, I wanted to make another animation of some part of the Arctic, because things have been changing a bit faster lately. Second, I've been planning to write a piece about the Beaufort Gyre for a while now, except that I cannot bake a whole blog post from it. Third and last, in the comments we had been discussing those huge swathes of red, yellow and green (and even a bit of blue) on the Cryosphere Today daily ice concentration animated map that have been showing up and disappearing again in the last two weeks. Some people remarked that this most probably had to do with melt ponds that more or less distort the reported ice concentration picked up by the satellite sensors.
So, let's start with explaining what the Beaufort Gyre is. The Lord praise the man who invented copypaste and also Ole Nielsen, who has written an excellent informative synopsis on his weblog:
The Beaufort Gyre is an ocean and ice circulation pattern in the
Beaufort Sea, north of Alaska. I have marked it with a B on the map.
This gyre moves in a clockwise direction. This circulation results from an average high-pressure system
that spawns winds over the region. Ice that forms in or drifts into the
Beaufort Gyre has historically remained in the Arctic ice system for
years, accumulating snow and thickening each winter. Beginning in the
late 1990s, the ice began melting away while in the southern parts of
the gyre, before completing the circulation.
The short story is that Beaufort gyre is a result of the Coriolis
force, the prevailing winds, and what is known as Ekman transport (in short: movement of water at a certain angle
to the wind).
In Patrick Lockerby's latest piece, Arctic Ice June 2010 - Solstice Update, there's a recent picture from the MODIS Arctic Mosaic. As Patrick writes:
Ice color is a fairly good indicator of ice condition if the image resolution integrates polynyas and meltwater pools so as to make the ice look bluish-grey. The image below shows whiter ice within the circle and bluish ice outside of it. The Arctic mosaic images show the bluish-grey areas as highly fragmented, mobile and melting ice. That rotten ice probably won't last long. I give it 4 to 6 weeks.
I suggest that you have a look at some of that rotten ice in the
Rapidfire images and then compare what you see with the following
Cryosphere Today image.
So here's where my animation comes in. I've decided to concentrate on the MODIS Terra 1km True Color image (r05_c03) that shows the big polynya off the coast of Barrow and a big chunk of the eastern part of the Beaufort Sea. The animation shows the past 3 weeks, from June 3rd to June 23rd. Here it is (click for a larger version):
The first thing to notice of course is the Beaufort Gyre in action. This has already made the making of the animation worthwhile, but there's more. If you focus on the upper left corner you can see these huge ice floes being moved and then broken up by the Gyre. In my opinion this looks kind of spectacular, just like that block of ice that blocked the Nares Strait for three minutes and a half. Furthermore, you can see two even bigger ice floes in the middle left of the picture that also seem to be in the process of being shattered into a million pieces.
And last, but certainly not least: You can clearly see the ice mass changing colour around day 159 (June 8 2010). Now compare that to the same date on the Cryosphere Today 30 day animation. The colour in the animation gets a bit darker, but doesn't change much after that. On the CT animation you see that huge swath of red, yellow and green revert back to pink and purple. Could it be that the sensors get tricked by the ice changing colour and getting darker, and that this then is accounted for the following days?
Anyway, I hope you like this newest animation. I'm hoping the Siberian side of the Arctic becomes a little less cloudy for my next animation.