Variations Of The Spring Extreme Precipitation Over Eastern Southwest China And Possible Mechanisms

This study analyzed the variations of spring extreme precipitation over eastern Southwest China(SWC)during 1961-2020,and further explored the atmospheric and oceanic anomalies which have influence on the variations of the extreme precipitation.The major conclusions are summarized as follows:(1)There is a significant difference in the extreme precipitation between eastern and western SWC.And the leading mode of spring extreme precipitation over SWC mainly reflects the variations of spring extreme precipitation over eastern SWC.The spring extreme precipitation in eastern SWC experienced two significant interdecadal changes,with interdecadal decrease around the early 1980 s and interdecadal increase around the late 1990 s.In addition,the spring extreme precipitation over eastern SWC exhibits significant periodic variations of 2-4-year and quasi-8-year.(2)The East Asian trough(EAT)can significantly influence the variations of spring extreme precipitation over eastern SWC after the late 1980 s.After the late 1980 s,the EAT variability are significantly increased,and its related atmospheric circulations are also enhanced and with a larger extent.Therefore,the EAT can influence the eastern SWC,resulting in anomalous moisture and dynamical conditions and consequently leading to anomalous spring extreme precipitation over the region.(3)The spring extreme precipitation over eastern SWC is associated with two different atmospheric teleconnection patterns over the periods before and after the late1980 s,respectively.Before the late 1980 s,the extreme precipitation is related to a Rossby wave train originating from the high-latitude North Atlantic and propagating across eastern Europe and western Siberia to East Asia.After the late 1980 s,the extreme precipitation is related to another Rossby wave train originating from the mid-latitude North Atlantic and propagating across the Scandinavian Peninsula and western Siberia to East Asia.These two Rossby wave trains can affect the water vapor transport to eastern SWC,consequently leading to anomalous spring extreme precipitation over the region.(4)The sea surface temperature(SST)tripole pattern over the North Atlantic(NAT)and dipole pattern over the South Indian Ocean(SIOD)pattern in preceding winter can influence the spring extreme precipitation over eastern SWC over the periods before and after the late 1980 s,respectively.Before the late 1980 s,the preceding winter NAT can excite a Rossby wave train in spring,which propagates eastward to East Asia and changes the water vapor conditions over eastern SWC,consequently resulting anomalous spring extreme precipitation over the region.After the late 1980 s,the preceding winter SIOD can change the convective activities over tropical Indian Ocean in spring,and further enhances the anticyclonic circulation over the western North Pacific and local meridional circulation over the China-Indochina Peninsula to South China Sea,leading to anomalous moisture and dynamical conditions and extreme precipitation over eastern SWC.The preceding winter signals of the two SST patterns could be served as potential prediction sources for the spring extreme precipitation over eastern SWC during the two periods.