Interannual Variations Of Summer Precipitation In Southwest China:Anomalies In The Moisture Transport And Roles Of The Tropical Atlantic

Based on the observed and reanalysis data,conventional statistical methods,the HYSPLIT model and CAM5.3 atmospheric model,contributions of moisture from the Indian Ocean(IO),South China Sea(SCS),adjacent land region(LD)and Pacific Ocean(PO)to interannual summer precipitation variations in Southwest China(SWC)are investigated.And the probable mechanism of tropical Atlantic SST on summer precipitation in Southwest China(SWCP)is revealed and verified.The main conclusions are as follows:(1)IO and SCS surface evaporation is the most important source of water vapor to contribute to Southwest China summer precipitation(SWCP).On average,the IO,SCS,LD,and PO contribute 48.8%,21.1%,23.6% and 3.7% of the total moisture release in SWC,respectively.In summers with the above-normal precipitation,moisture release from the IO/SCS increases by 41.4%/15.1%,significantly.In summers with the below-normal precipitation,moisture release from the IO/SCS/PO decreases by 44.2%/24.6%/22.3%,significantly.Besides,the moisture anomalies from the four source regions together explain 86.5% of the total interannual variances of SWCP,in which the IO and SCS can explain 75.7%.(2)Variations in moisture transport from the IO,SCS and LD to SWC are not independent to one another and commonly influenced by the anomalous anticyclone in the Western North Pacific(WNP),which enhances the moisture transport from the IO and SCS by the anomalous southwesterlies over its northwestern quadrant but reduces that from the LD east of SWC by the anomalous westerlies along its northern frame.(3)The interannual variation of SST in the tropical Atlantic is an important cause of anomalous anticyclone in the northwest Pacific.The tropical Atlantic(10?W-15?E,5?S-5?N)sea surface temperature index ATL is defined,and the coefficient of correlation with SWCP is 0.52,significant at the 99.9% confidence level,indicates a statistically significant association.The analysis of large-scale circulation anomalies shows that anomalous warming in the tropical Atlantic can modify the Walker circulation,induce anomalous descending motion over the central tropical Pacific and excite the anomalous anticyclone in the WNP as the classic Matsuno-Gill response.The observed impacts of the tropical Atlantic warming on the anomalous anticyclone and summer precipitation in SWC can be well reproduced in an atmospheric general circulation model.(4)The control experiment(CTL)of CAM5.3 model can well reproduce the climate state of large-scale circulation,indicating that the model has good simulation performance.The sensitivity experiment(SEN)can reproduce and verify the effect and physical mechanism of tropical Atlantic warm SST on the anomalous anticyclone in the NWP.