Co-Effects Of Upper-Level Subtropical Westerly Jet And Low-Level Southern Branch Trough On Winter-Time Heavy Rainfall Over Southern China

This paper uses NOAA global daily precipitation analysis data and NCEP/NCAR global re-analysis daily average data to identify the heavy precipitation process that occurred in the southern region of China from the perspective of meteorology to 10 winters,and objectively identified the events of the south branch trough containing mobility characteristics from the perspective of Lagrange.On this basis,from the perspective of combining meteorology and climatology,the collaborative effect of the low-layer south branch trough and its high-rise subtropical westerly wind rapids on the winter heavy precipitation in southern China is revealed.The results show that:(1)In winter,the heavy precipitation in the southern region of China is mainly concentrated in south China south of 30 ° N and east of 110 ° E,while the southwest region west of 110 ° E has relatively little precipitation.(2)The southern branch of the middle and low tropospheric is one of the key weather systems affecting the occurrence of heavy winter precipitation in the southern region of China.The mode of precipitation affecting the southern region of China with mobility characteristics is mainly manifested as a latitudinal heavy rainfall belt extending from the southwest region to the east to the south of china.In this context,the main circulation situation of heavy precipitation is manifested as a large-scale subtropical south branch westerly wind system with high and low circulation anomalies.There are covariant characteristics in the subtropical south branch westerly rapids in the upper tropospheric and the south branch trough in the middle and lower layers,which have a collaborative effect on the heavy precipitation in the southern region of China.(3)When the east-passing wave column of the high-rise south branch rapids is coordinated with the low-level south branch trough,the caused by the latitudinal strong precipitation belt extending from the southwest region to the south china region is stronger than the precipitation intensity under the influence of the south branch trough alone.The results of composite analysis and typical case analysis indicate that the Rossby wave train traveling eastward along the upper-level subtropical westerly jet can influence the upper-level jet pattern and the lower-level southern trough over East Asia,and then modulate the precipitation anomaly in southern China.Its influence mechanism mainly has the following two aspects: First,the east-passing wave column of the high-rise subtropical jet stream affects the pattern of the high-altitude subtropical rapid in East Asia through the interaction of wave currents,which in turn promotes the secondary circulation of the East Asian high-altitude rapids to induce strong upward movement in its inlet area,providing favorable power conditions for precipitation anomalies in the southern region.Second,the high-rise rapids east wave column can strengthen the development of the south branch trough in the middle and low troposphere through the diagonal pressure potential propagation and conversion,which in turn makes the water vapor transport and radiation rise movement conditions in front of the south trough more conducive to the occurrence and development of heavy precipitation in the southern region of China.