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

Extreme cold winter weather events have more frequently occurred during the recent decade than before over the Eurasian continent. Various contributing factors have been examined, such as changes in the atmospheric circulation, enlarged jet stream amplitude, and anomalous snow and sea ice forcing. However, it remains unclear how the internally or externally changed large-scale atmospheric dynamics has driven daily-based extreme cold events. In this study, we investigated variability of and changes in extratropical cyclones and anticyclones and their role in modulating winter climate over Eurasia. The major approach employed is a modified automated cyclone and anticyclone identification and tracking algorithm. Our results indicate a negative correlation of -0.7 of the regional mean intensities between cyclones and anticyclone during 1978/79-2011/2012 winter seasons. In conjunction with an intensified anticyclones, the frequency of Ural blockings has increased. As a consequence, anomalous winter season anticyclonic circulation has occurred, advecting cold air southward to and serving as a fundamental mechanisms for causing extreme cold events over the Eurasian midlatitude. Southward extension of snow cover in the preceding autumn has also reduced absorption of downwelling shortwave radiation, furthering the cooling processes. Relationship between the synoptic anticyclone activities and the Barents-Kara seas sea ice change was also examined to identify underlying physical mechanisms.