Comparative Study On Influence Of The India-Burma Trough On Precipitation In Southwest And South China

The India-Burma trough is one of the main weather systems affecting the precipitation in southern China.Based on the NCEP-DOE R II reanalysis data,ERAInterim reanalysis data and precipitation data from China Meteorological Administration,this paper investigated the influence of the India-Burma trough on precipitation events in southern China during the winter half year(October to May of the next year)in the past decade(2009-2018).The events affecting precipitation in China by the India-Burma trough mainly be divided into three types:(1)The India-Burma trough is stable(in the north of the Bay of Bengal),which affects the precipitation in southwest China.(2)The India-Burma trough moves eastward,affecting the precipitation in South China.(3)The India-Burma trough(in the northern region of the Bay of Bengal)is stable,affecting the precipitation in South China.The survey results of various events show that in the cases where the India-Burma trough affects the precipitation in the south of China in the winter half year,the stable maintenance of the India-Burma trough affects the precipitation in the southwest of China for 25.4%.As the India-Burma trough moved eastward,it affects the precipitation in South China for 38%.The proportion of precipitation in South China is 16.9% when the India-Burma trough is maintained in the Bay of Bengal.The results of the combined analysis of various events and the analysis of typical cases show that there are significant differences in the circulation characteristics and influencing mechanisms of the India-Burma trough affecting the precipitation in southwest and south China.(1)When the India-Burma trough affected the precipitation in southwest China,it is stable and maintained with strong intensity;The subtropical high retreated eastward,and the center of the upper-level jet stream was west-south.When the India-Burma trough moves eastward to the south China precipitation,the mean position of the India-Burma trough is eastward but the intensity is weak.The subtropical high extends westward and the center of the upper-level jet stream is eastward.When the IndiaBurma Trough moved less precipitation in South China,the India-Burma Trough remained stable but the intensity is weak.The subtropical high extends westward and the center of the upper-level jet stream is northward.The subtropical high and the upper-level jet stream cooperated well with the India-Burma trough during the precipitation process in southern China.The meridional circulation is the main circulation pattern in the subtropics and middle latitudes when the India-Burma trough is stable in the northern part of the Bay of Bengal.When the India-Burma trough moved eastward,the circulation pattern was mainly zonal.(2)The influence of the India-Burma trough on the precipitation in Southwest China is greatly affected by the topography,and the precipitation mainly occurs on the windward slope of the southwest mountains.The main precipitation mechanism is "the forced uplift of the low-level terrain and the coupling effect of the upper-level jet stream".The India-Burma trough not only plays a role of water vapor transportation,but also plays a significant dynamic role on the precipitation.However,the influence of the India-Burma trough on the precipitation in South China is mainly related to the baroclinic frontogenesis formed by the intersection of warm and cold air.The dynamic mechanism of precipitation is mainly "baroclinic precipitation formed by the intersection of warm and cold advection",and the secondary circulation of upper-level jet stream also has a certain contribution.The contribution of the India-Burma trough to precipitation is mainly water vapor transport.