Plot of the month for March 2017 is from recent published work by Reinhard Schiemann et al., who study how the representation of Northern Hemisphere blocking changes with increasing resolution across different global GCMs.

Blocking refers to the occurrence of quasi-stationary high pressure systems in midlatitude regions. These blocking highs typically persist for several days to weeks and often divert cyclones traveling in the storm track regions poleward or equatorward. In the Northern Hemisphere, preferred regions of blocking occurrence exist: the eastern sides of the Atlantic and Pacific Oceans. Blocking occurs throughout the year, peaking in boreal winter and spring. The persistent circulation during blocking episodes can lead to extreme weather events; recent examples include the cold European 2009/10 winter and the 2010 Russian heat wave.

We evaluated how well different climate models represent atmospheric blocking situations during sprint (March-May; see figure).

Figure | Spring blocking frequency in reanalysis (a), low-resolution (d-e) and high-resolution (f-i) atmosphere-only simulations. (Click the image for a larger version.)

 

The figure shows (a) an observation-based reference climatology, (b-e) blocking climatology as represented by four low-resolution climate models, (f-i) blocking climatology of the same four models at higher resolution. For the season shown (spring), there is a clear improvement with resolution in how the models capture blocking in the Euro-Atlantic sector. While there is a general improvement at higher resolution, it is smaller for some other seasons/models, and considerable blocking biases remain even in state-of-the-art high-resolution models. Understanding and improving these biases is an area of active research.

 

This research is published: Schiemann, R., M.-E. Demory, L. C. Shaffrey, J. Strachan, P. L. Vidale, M. S. Mizielinski, M. J. Roberts, M. Matsueda, M. F. Wehner, and T. Jung (2017). The Resolution Sensitivity of Northern Hemisphere Blocking in Four 25-km Atmospheric Global Circulation Models. Journal of Climate 30, 337-358 (doi:10.1175/JCLI-D-16-0100.1).

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