Summer Water Vapor Characteristics And Causes Of Precipitation Changes In The Eastern Part Of Southwest China In The Past 60 Year

In this paper,the characteristics of water vapor in summer over eastern Southwest China(ESWC)during 1961-2020 were analyzed,including the water vapor transport,water vapor source and water vapor content.On this basis,the reasons for the difference in the distribution of summer precipitation conversion between east and west were analyzed,and the promotion effect of terrain on summer precipitation in the region was verified by numerical model.Finally,the possible causes affecting the interannual variation of summer precipitation in the eastern part of Southwest China are discussed.The following results are obtained:(1)The Brubaker binary model was used to analyze the source and contribution of external water vapor in summer over ESWC.In terms of climate,93.59% of the precipitation is caused by external water vapor transport,while 6.41% is caused by local evaporation.In the external water vapor transport,the southern boundary(73.90% contribution rate)and the western boundary(19.24% contribution rate)contribute more water vapor.From the perspective of interannual and interdecadal,the magnitudes of the precipitation generated by external water vapor transport and the regional average precipitation are similar and the change trend is consistent,while the precipitation generated by local evaporation is much smaller than the regional average precipitation and has the characteristics of reverse change,indicating that the contribution of external water vapor transport will increase while the contribution rate of local evaporation will decrease relatively when the precipitation is large,and vice versa.(2)It is found that Arabian Sea,Bay of Bengal,Western Pacific,Northwest water vapor channel 1 and Northwest Water vapor channel 2 are main water vapor sources over the ESWC in summer.The Bay of Bengal channel has the largest contribution of water vapor,followed by the Western Pacific channel and the Arabian Sea channel,and the two Northwest channels have a smaller contribution.(3)Influenced by the topography of the region,the summer precipitation in the ESWC is more in the east and less in the west,the water vapor content is more in the southeast and northwest,and the water vapor content is less along the southwest to northeast.Therefore,the precipitation conversion rate also presents the characteristics of greater in the east and smaller in the west.Based on the mesoscale numerical Model of Weather Research and Forecasting Model(WRF),terrain sensitivity tests are carried out to reveal the role of terrain in monthly time scale precipitation and rainfall during rainstorm,and it is found that terrain has significant influence on precipitation intensity within the region.In particular,the precipitation in the southeastern part of the region will decrease by 9.89% and 19.90%,respectively,on the monthly time scale after the topographic height is reduced by half and the topographic height is removed.Therefore,promoted by the windward slope of the mountains,the precipitation conversion rate is higher in the southeast of the region,but lower in the northwest.(4)On the scale of interannual variation,the first two modes of summer precipitation in the ESWC are the uniform model across the region and the reverse model between the north and south.Tripolar sea surface temperature(SST)anomalies in the North Atlantic Ocean and the sea ice anomaly in the Barents Sea have a significant effect on the main modes of summer precipitation in the ESWC by modulating the quasi-zonal wave train in the troposphere.The zonal wave train originates from the northwest Atlantic Ocean,passes through the Norwegian Sea and Western Europe,and finally reaches the ESWC.The wave energy strengthens the cyclonic anomaly in the north and anticyclonic anomaly in the south in the ESWC,and finally leads to the increase of summer precipitation.