Impact of May soil moisture anomalies in China on the interannual varia-tion of July precipitation dipole over South China and the eastern Tibetan Plateau
During the period of 1979-2019,there was a significant negative correlation between the interannual variation in precipitation anomalies over South China(SC)and those in the eastern Tibetan Plateau(ETP)in July,with a correlation coefficient of-0.60 between the area-averaged precipitation over the two regions.It is sta-tistically significant at the 99％confidence level.Therefore,a precipitation dipole index(PDI)is defined as the difference in the standardized area-averaged precipitation between SC(20°-26°N,108°-123°E)and the ETP(28°-35°N,90°-108°E)in July.The positive phase of the July precipitation dipole is characterized by in-creased(decreased)precipitation over SC(the ETP),and vice versa.Based on this,we utilize ERA5 reanalysis data and station precipitation data from the period of 1979-2019 to investigate the influence of soil moisture a-nomalies in May on the interannual variation of the July precipitation dipole,along with its underlying physical processes.The study results show that higher soil moisture in the TP and lower soil moisture in Central China(CC)in May tend to lead to increased(decreased)precipitation over SC(the ETP)in July,displaying a dipole pattern of precipitation over the two regions.Further analysis reveals that the positive(negative)soil moisture a-nomalies in the TP(CC)may persist from May to July,resulting in positive surface turbulent heat flux anomalies in the Northern China(NC)region in July.This in turn causes local middle to lower troposphere warming,thus intensifying the meridional temperature gradient and atmospheric baroclinicity between NC and Lake Baikal.Cor-respondingly,enhanced synoptic-scale transient wave activity is observed,which creates an anomalous high pres-sure with an equivalent barotropic structure and Rossby wave sources over NC-Mongolia by transient vorticity forcing.The associated Rossby waves propagate southeastward to SC.Subsequently,an anomalous low pressure appears over SC with an equivalent barotropic structure,which facilitates the eastward shift of the western Pacific subtropical high and westward shift of the South Asian high.This anomalous circulation respectively corresponds to anticyclone and cyclone anomalies in the middle and lower troposphere over Mongolia and SC,and conse-quently enhanced(suppressed)precipitation occurs in SC(the ETP).In addition,the positive feedback process between the anomalous high over Mongolia and local low soil moisture is favorable to the formation of the July precipitation dipole by intensifying and maintaining the above physical process,and vice versa.
soil moisture in Maya dipole pattern of precipitation over South China and the eastern Tibetan Plat-eau in Julyinterannual variabilityphysical mechanism
万方数据
维普
