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Saturday, September 8, 2012

New contender for scariest graph you'll ever see: June-August 2012 sea level pressure (mb) composite anomaly [1981-2010 climatology]

Signs of Arctic climate change

by neven acropolis, Arctic Sea Ice Blog, September 8, 2012
And when I say 'Arctic,' I of course automatically imply 'Northern Hemisphere'. You know, the place where most of the world's agriculture is based.
One thing I have noticed this melting season, is how high-pressure areas persistently remained over Greenland (causing, for instance, the decrease in reflectivity all over the ice sheet):
But what I didn't know, is that this is something that apparently started in 2007, having all kinds of consequences for Northern Hemisphere weather patterns. This is again from the Dosbat blog, where Chris Reynolds is on a roll:

Last year I posted "Summer Daze." In that post I detailed a new pattern of atmospheric behaviour centred on high pressure over Greenland, this pattern is new since 2007, and as I showed is a robust change since the 1950s in NCEP/NCAR data.

Well, it's happened again this year...
The pattern I showed consisted of strongly anomalous high pressure over Greenland surrounded by a ring of tendency to low-pressure anomalies. I used NCEP/NCAR monthly analysis to examine it (source data). As with all atmospheric patterns, in some years it was stronger than others, and there was interannual variability in the details of the pattern, but taking a succession of years it was seen to be a common pattern. The robustness of this pattern and its unusual nature is highlighted by taking the average pressure fields for batches of years and subtracting one batch from another. The pattern of the post 2007 period survives this method, still being present for any 5-year period subtracted from the period 2007 to 2011. As could be seen from the original Summer Daze post, this process shows that the pattern doesn't occur regularly in the past in the way it has done since 2007.

This year the pattern is textbook perfect.
Chris goes on to explain what this means for UK summer weather and wonders if perhaps, possibly, maybe, this persistent blocking pattern could have something to do with disappearing Arctic sea ice. Read the whole article here.
I'm sure Chris will have more to say about this, and scientific experts won't be slow to follow.

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