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Modelling Northern Hemisphere Atmospheric Blocking Systems

Paper Reviewed
Davini, P. and D'Andrea, F. 2016. Northern Hemisphere Atmospheric Blocking Representation in Global Climate Models: Twenty Years of Improvements? Journal of Climate 29: 8823-8840.

The authors of this intriguing paper, Davini and D'Andrea (2016), begin by explaining that atmospheric blocking is a mid-latitude weather phenomenon that is characterized by the long-lasting persistence of a quasi-stationary high-pressure system that blocks and diverts the movements of synoptic cyclones, which phenomenon typically occurs following the breaking of a Rossby wave at the end of a storm track. Unfortunately, however, they report that this phenomenon represents "a considerable source of error for general circulation models."

This being the case, the two French scientists go on to describe how they analyzed twenty years of global climate model (GCM) projections of this phenomenon in the Northern Hemisphere in an attempt to learn more, making use of a series of equivalent metrics of three generations of GCMs -- AMIP (1982), CMIP3 (2007) and CMIP5 (2012) -- which together comprise a total of 95 different models. And what did they thereby discover?

Davini and D'Andrea report that although "some models positively react to improved sea surface temperatures, others even deteriorate their blocking climatology." And they thus conclude that "although the overall picture seems somewhat discouraging -- with good improvements over the Pacific but negligible advancements over Euro-Atlantic blocking in 20 years -- the modelling community appears to be moving on the right track." And so they conclude that "it is likely that the problem of blocking simulation in GCMs will be significantly alleviated in future years." But when in the future that might occur, God only knows.

Posted 21 February 2017