The Relationship Between SO And Rainfall In The Maritime Continent During Boreal Summer:Interannual And Interdecadal Changes

By using the NOAA precipitation data,the Southern Oscillation Index(SOI)and NINO3 index,the monthly mean data from NCEP/NCAR Reanalysis and CMAP,the monthly mean sea surface temperature data from Hadley Center over the period of 1960-2016,we have systematically investigated the variation of SO(Southern Oscillation)and its association with Asian African monsoon circulation and regional climate variation in the Maritime Continent(MC)during boreal summer.The main conclusions are as follows:The SO has significant inter-annual variability,which has important influence on the circulation,precipitation and temperature over Asian-Australian monsoon region and the Maritime continent during boreal summer.When SOI is in its positive phase,there is cyclonic circulation in the upper troposphere and anticyclonic circulation in the lower troposphere over eastern region of Australia in the north of the equator and eastern area of the east China sea.As the result the lower tropospheric divergence and upper tropospheric convergence over the region of Pacific in the north of the equator facilitate the maintenance of descending motion.Over Kalimantan,the lower tropospheric convergence and upper tropospheric divergence is favorable for the ascending motion.The precipitation anomalies are positive in the Maritime continent and negative in east Asia.The temperature anomalies are positive in the Maritime continent and Tibetan plateau to east China sea,and negative over bay of Bengal and Indian peninsulaWhen removed Nino3 signal,SLPA of Darwin and Tahiti station are independent,and related circulation field has great difference,which has different influence on climate variation of MC area.When SLPA of Darwin station is positive(negative),SST of west equatorial pacific is positive(negative),too,there is no significantly increasing and sinking motions on equatorial area.Over MC area,water vapor convergence and rainfall is below normal.Temperature over northern australia and southern of MC area is negative(positive).When SLPA of Tahiti station is positive(negative),Over 150°W,the lower tropospheric convergence and upper tropospheric divergence facilitate the maintenance of descending motion.Over MC area,water vapor divergence,rainfall and temperature are more than normal.Usually when SOI is positive(negative),precipitation anomaly over MC is positive(negative),too.Our results show that the correlation between SOI and summer precipitation over MC area has significantly weakened since 1998.The reason for this phenomenon is that the correlation of SOI and sea surface temperature(SST)is negative in the central Pacific.The negative correlation center has shifted eastward and manifested as CP-type SSTA after1998.This type of SSTA corresponds to the center of apparent heat source anomalies located in the central Pacific,which induces the Gill-type response of atmosphere,leading to an anomalous anticyclonic circulation in the lower troposphere east of the Philippines and hence to strengthening the divergence there.This causes the precipitation over area north of equator to significantly decrease,canceling the precipitation increase over southern part of the MC,making the relationship between the precipitation and SOI to loose.