Radically Shifted Atmospheric Circulation and Intensified Anticyclones: Causes of Recent Extreme Cold Weather Events in Eurasia

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Wednesday, 5 February 2014: 11:30 AM
Georgia Ballroom 1 (The Georgia World Congress Center )
Xiangdong Zhang, University of Alaska, Fairbanks, AK; and C. Lu and Z. Guan

Handout (4.4 MB)

Extreme cold winter weather events have occurred more frequently in recent years in East Asian, as well as broadly in Eurasia in conjunction with global mean surface air temperature increase. To gain insight into this regional mismatch with the global warming trend, we analyzed winter cyclone and anticyclone activities, and their interplay with the regional atmospheric circulation pattern characterized by the semi-permanent Siberian high. We found a persistent weakening of both cyclones and anticyclones between the 1990s and early 2000s, and a pronounced intensification of anticyclone activity afterwards. This intensified anticyclone activity is suggested to drive the substantially strengthening and northwestward shifting/expanding Siberian high, and explains the decreased mid latitude Eurasian surface air temperature and the increased frequency of cold weather events. The weakened tropospheric mid latitude westerlies in the context of the intensified anticyclones would reduce the eastward propagation speed of Rossby waves, favoring persistence and further intensification of surface anticyclone systems.