Cyclone and Anticyclone Activities Impact Eurasian Surface Climate and Cause Extreme Cold Events ?

Abstract:

Extreme cold winter weather events have more frequently occurred during recent decades over the Eurasian continent, in conjunction with the rapidly warming Arctic. Although various contributing factors have been examined, including changes in the atmospheric circulation, increase in meridional span of jet stream fluctuation, and anomalous snow and sea ice forcing, it still remains unclear how internally or externally altered large-scale atmospheric dynamics has driven daily-based extreme cold events. In this study, we further investigated variability of and changes in extratropical storm tracks and anticyclones and their resultant dynamic and thermodynamic role in causing extreme cold weathers over Eurasia. The major approach employed is a modified automated cyclone and anticyclone identification and tracking algorithm. Our results reinforced our previous finding that storms have weakened and anticyclones have intensified over Eurasia during 1978/79–2011/2012 winter seasons. Corresponding to these long-term changes, anomalous high pressure occurred over the Ural area, providing fundamental dynamic setting favoring occurrence of blocking events. As a consequence, polar cold air was advected southward to the midlatitude, causing extreme cold events. Along with this dynamic process, snow cover also extended southward to reduce surface absorption of downwelling shortwave radiation and further the cooling process. Barents-Kara sea ice forcing was examined to identify underlying physical mechanisms for changes in storm tracks and anticyclone activities.