Relationship of Synoptic-Scale Transient Eddies and Extreme Winter Precipitation Events in the Middle and Lower Reaches of the Yangtze River

The association of extreme winter precipitation events in the middle and lower reaches of the Yangtze River including synoptic-scale transient eddies is examined by using the ERA40 and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data and daily rainfall data reported by 85 stations. A close relationship is detected between extreme precipitation events and transient eddies. In winter, two branches of synoptic-scale transient eddies are accompanied by subtropical and polar-front jets, respectively. It is demonstrated that the south branch of the transient eddies differs during highly and less frequent years of extreme precipitation events. Overall, transient eddies become active and strong, and they spread continuously with long durations over Eurasia during highly frequent extreme precipitation years; the reverse occurs for less frequent years. To some extent, the intensity and energy of the transient eddies both experience similar variations from the daily frequency of extreme precipitation. Moreover, the northern branch of the transient eddies and their water vapor transport are favorable for the occurrence of extreme precipitation events. Therefore, extreme winter precipitation events have a close relationship with the synoptic-scale transient eddy, implying the activity and propagation of transient eddies may be important factors in extreme precipitation events. This study is expected to provide a new perspective for the causes of extreme precipitation.