Characteristics Of Subseasonal Scale Zonal Movement Of Wpsh In Summer And Its Relationship With Precipitation In Southwest China

This paper from the perspective of sub-seasonal scale,firstly,focuses on the characteristics of the Western Pacific Subtropical High(WPSH)zonal movement and its influence on early summer and late summer precipitation in southwest China.Secondly,the HYSPLIT model is used to simulate the moisture transport trajectory that affects precipitation in the Southwest China during the zonal anomaly of the WPSH;Finally,the relationship between the sub-seasonal zonal movement of the WPSH and the local SST anomaly in the Western Pacific is analyzed.Define the east-west variation index of the WPSH in early summer and late summer respectively according to the location of the key area of the zonal movement of the WPSH.This index has a significant 10-30 days sub-seasonal cycle,and it can well characterize the Characteristics.According to the standard value of the index,195 events(1374 days)were selected in early summer and late summer events.We further analyzed the east-west events,which showed that the variation of the WPSH zonal movement on the sub-seasonal scale was closely related to the precipitation in the Southwest China.During the west(east)events of the WPSH,the WPSH experienced a process of gradually changing from east ? west ? east(west ? east ? west),and the corresponding precipitation in most regions of the Southwest experienced a gradual change from less ? more ? less(more ? less ? more)evolution,the response of southwestern precipitation to change of the WPSH on the sub-seasonal scale has a great relationship with the vertical changes of moisture and airflow currents on the north side of the WPSH and the main area of the WPSH during zonal movements.The precipitation shows a dipole distribution from southwest to northeast in early summer,however,the consistence of precipitation changes is better in late summer.The results of HYSPLIT model show that there are three moisture transport trajectory that affect precipitation in southwestern China: the southwest transport trajectory,the east transport trajectory,and the north transport trajectory.In early summer,for the northern regions,the east airflows dominants in both of west and east events,and the stronger east airflows caused more precipitation;For the middle regions,during the west(east)events,the southwest airflows and the north airflows are strong(weak),the east airflows are weak(strong),and the precipitation is more(less);For the southern regions,the Southwest airflows dominates in both of west and east events,but during the east events,there is north cold airflows southward,Causes more precipitation.In late summer,except for the central Yunnan region,most of the other regions,during the west(east)events,the southwest airflows are strong(weak),the east airflows and the north airflows are weak(strong),and the precipitation is more(less).The air-sea interaction plays an important role in the zonal movement of the WPSH.Whether it is early summer or late summer,during the west events,in the early stage of the WPSH extends westward,the local cold SST(Sea Surface Temperature)anomalies in the Western Pacific force the lower atmosphere to be relatively stable,,weakened the abnormal cyclone in the key area,and generated abnormal anticyclones on the east side,which caused the WPSH to start extending westward;During the westward extension of the WPSH,the convective activity in the key area is restrained,and the net radiation flux received by the ocean surface is enhanced,which lead to the increase of SST;Increasing warm SST force lower atmospheric instability to increase,the convective inhibition decreases,which weakens the abnormal anticyclone in key area and causing the WPSH to retreat eastward.During the east events,this relationship is just the opposite.