Using GPCP daily rainfall and ERA-Interim reanalysis data and NOAA’s daily climate data record of OLR from period 1979-2015,we investigate the distinct features of subseasonal zonal oscillation of the east edge of South Asian High(SAH)during early and late summers.The relationship between the subseasonal zonal oscillation of SAH and persistent heavy rainfall events over China is revealed.The HYSPLIT(Hybrid Single Particle Lagrangian Integrated Trajectory Model)model and NCEP/NCAR reanalysis data were used to analyze the characteristics of water vapor transport over the core regions of anomalous precipitation during eastward and westward extension events of SAH on subseasonal time scales in the two subseasons.When the SAH approaches its eastern most position,the associated anomalies in atmospheric circulatioin and precipition exhibit similar characteristics in both the early and late summers:(1)In the middle-to high troposphere,when the anomalous anticyclonic circulation among a eastward propagating wave train across Eurasia migrate to eastern Tibetan Plateau(TP),the SAH extends eastward while the WPSH extends westward.The SAH and Western Pacific Subtropical High(WPSH)move either toward or away from each other on the subseasonal time scales.(2)A dipolar structure of positive rainfall anomaly to the north of 30° N and negative rainfall anomaly to the south of 30’ N is found in China,the subseasonal variations of vertical motion,water vapor flux and its divergence are in favor of the generation and maintenance of such dipolar structure.When the SAH extend eastward,the associated anomalies also display different characteristics during early and late summers:(1)Compared to the early summers,the subseasonal geopotential height anomalies in the troposphere in late summers are a bit more intensified.(2)The dipolar structure of rainfall anomaly locates over eastern China in early summers resulting in enhanced rainfall in Yangtze-Huaihe River Valley(YHRV)and reduced rainfall in southeastern coast of China.In the late summers,the rainfall anomaly dipole moves westward to middle China,inducing positive rainfall anomaly in Sichuan Basin and negative rainfall anomaly in the Yunnan-Guizhou Plateau.(3)There is a close connection between the subseasonal zonal oscillation of SAH and persistent heavy rainfall(PHR)events in China.When SAH extends eastward,the region of high frequency PHR locates over the Yangtze-Huaihe River Valley in early summers and over the Sichuan basin in late summers.The analysis of HYSPLIT model shows that:(1)In the early summers,compared with the SAH’s westward extension events,the SAH’s eastward extension events are more conducive to moisture being transported from southern moisture sources to YHRV.The associated anomalous upward motion in YHRV together with the moisture condition lead to enhanced rainfall and more PHR events in this region.(2)In the early summersthe total amount of water vapor transported to southeastern coast of China in the early summer during eastward events are equals to that in westward events,which indicates that the rainfall anomalies in this region are mainly affected by dynamic conditions.When SAH extends eastward(westward),the associated anomalous downward(upward)motion is the main factor to reduced(enhanced)rainfall in this region.Results in late summers are similar. |