Monthly Weather Review 2012 ; e-View
Leibniz-Institute of Atmospheric Physics at the University of Rostock, Kühlungsborn, Mecklenburg, GermanyKlaus Fraedrich
This study analyzes the large scale flow structure based on ERA-Interim data (1989 to 2010). The anomalous long-lasting blocking high over Western Russia including the heat wave occurs as an overlay of a set of anticyclonic contributions on different time scales: (i) A regime change in ENSO towards La Niña modulates the quasi-stationary wave structure in the boreal summer hemisphere supporting the eastern European blocking. The polar Arctic dipole mode is enhanced and shows a projection on the mean blocking high. (ii) Together with the quasi-stationary wave anomaly the transient eddies maintain the long-lasting blocking. (iii) Three different pathways of wave action are identified on the intermediate time scale (~ 10-60 days). One pathway commences over the eastern North Pacific and includes the polar Arctic region; another one runs more southward and crossing the North Atlantic, continues to eastern Europe; a third pathway southeast of the blocking high describes the downstream development over South Asia.