Spatial Pattern and Causes of Interannual Variability of Autumn Rainfall in Southwest China

Spatial pattern and mechanisms of interannual variability of autumn rainfall in Southwest China (SWC) are analyzed using rainfall data from weather stations in China and ERA-Interim reanalysis as well as Hadley Sea Surface Temperature (SST) data.Cluster analysis and Rotated Empirical Orthogonal Function have been applied in the present study.Based on differences in the interannual variability of autumn precipitation,SWC is divided into two parts:the eastern part and the western part.The interannual variability of rainfall,significant periods of oscillation,extremely dry or wet years and related atmospheric circulations are substantially different between the eastern and western SWC.The rainfall variability in the eastern SWC is closely related to tropical SST anomalies.The positive SST anomaly in the eastern Pacific Ocean can trigger anticyclonic circulation over the northwestern Pacific,while the dipole mode of SST anomaly in the tropical Indian Ocean with positive SST anomaly in the west and negative SST anomaly in the east can induce anticyclonic circulation over the Bay of Bengal.As a result,the atmospheric moisture transport to eastern SWC intensifies.However,the circulation patterns corresponding to rainfall anomalies in the western SWC in the three months of autumn are different.In September,the western SWC is under control of the anticyclone over the Indochina Peninsula.In October,the anticyclone to the east of the Tibetan Plateau and the low trough over the Bay of Bengal work together to determine precipitation in the western SWC.In November,anomalous atmospheric circulation over the mid-high latitudes plays an important role for rainfall in the western SWC,which is highly negatively correlated with the Scandinavian teleconnection index.