资源环境科技发展态势分析平台

The formation of summer blocking events appears to have been mostly studied for a few individual events often associated with heat waves. Here we investigate summer blocking event dynamics in three areas over western Eurasia in order to draw some more general conclusions, mostly in terms of high- and low-frequency processes. A 2-D blocking event detection algorithm is applied to the 500-hPa-geopotential field from the ERA-40 and ERA-Interim reanalyses over the 1958-2017 period. It is shown that both high- and low-frequency processes are important to initiate blocking events over southern central Europe. Blocking events over western Russia are preceded by a significant low-frequency large-scale wave train, and their formation and maintenance are dominated by low-frequency processes only. Finally, it is shown that the risk of extreme seasons such as summer 2010 cannot be accurately estimated from the Poisson statistics of past events.

Plain Language Summary Atmospheric blocking events correspond to a large-scale reversal of the meridional pressure gradients that blocks the eastward propagating jet stream. In an atmospheric pressure chart, they are characterized by a large-scale high-pressure system. Blocking events strongly impact the weather mainly because of their persistence (up to 4-5 weeks), which allows anomalies in temperature to amplify. Because of their long persistence, they can be associated in summer with heat waves, which have major societal impacts (as in June 1976 in the UK, August 2003 in France, or July-August 2010 over eastern Europe and Russia). Blocking events dynamics has been less studied in summer than in winter, partly because of the smaller occurrence of blocking events in summer. Here we address the dynamical processes involved in summer blocking events over the European-western Russia region (where the 1976,2003, and 2010 blocking events occurred) to better understand what the key ingredients for their formation and dynamics are. To do that, we looked at blocking events in observations in summer over three key areas in the European-western Russia area. We show that western Russia is particularly prone to very long, high-impact blocks due to the nature of the atmospheric fluid dynamics that influences that region.