Favorable circulation patterns and moisture sources for wintertime extreme precipitation events over the Balkhash-Junggar region

The Balkhash-Junggar (B-J) region is a typical dryland region with strong sensitivity to climate change. The snowstorms of the year 2009 caused financial damage worth of 2,516 million RMB. This study examines the dynamical features and the moisture sources associated with wintertime extreme precipitation over the B-J region. The analyses are based primarily on the data set from ERA-Interim during DJF 1979-2017. Both Lagrangian and Eulerian approaches are used to examine the moisture sources. An upper-tropospheric Rossby wave train that extends from the North Atlantic Ocean to the B-J region is found to play a leading role in the formation of 127 wintertime extreme precipitation events in the B-J region. This Rossby wave train deepens a cyclonic anomaly in the lower troposphere over the B-J region, which favors the development of strong southwesterly moisture transport and strong updrafts there. These conditions are favorable for the occurrence of extreme precipitation events over the B-J region. Lagrangian moisture source analysis indicates that most of the moisture for precipitation during these events comes from terrestrial sources, with central Asia the key moisture source region. The Eulerian moisture budget analysis further shows that most of the moisture for extreme precipitation enters the B-J region through its western boundary via enhanced southwesterly flow. These dynamical and moisture source analyses establish a set of valuable precursor conditions for predicting wintertime extreme precipitation events over the B-J region.