Eastward Expansion Features Of The Southerly Wind On The Southeast Side Of Tibetan Plateau And Its Possible Response To Global Warming

Distinguished from the seasonal variation characteristic of the East Asian monsoon,the south wind prevails all the year over the southeast of Tibetan.This varies seasonally,moves eastward and can extend to the east of 115°E in the 15 th pentad.By utilizing the NCEP/NCAR reanalysis data,the annual variation features of the time of year-round southerly's eastward extension,the impact factor and its influences on precipitation of China are discussed.In addition,based on the CMIP5 model data,the response of year-round southerly to global warming are analyzed.The main results are shows as follow:(1)The interannual variations of the eastward extension time for the southerly are obvious.The eastward expansion occurs at February when earliest year,while the southerly wind doesn't begin to expand eastward until March in the late years.(2)The eastward extension impact on the climate of eastern China markedly.When the year-round southerly puts off extending eastward,the Spring Persistent Rains and quasi-stationary front in southern China will be weaker and the East Asian subtropical summer monsoon will delay its onset.In February and March,the precipitation increases from southern Bay of Bengal to eastern Philippines but decreases in southern China.In June,a South-North dipole-type precipitation anomaly is formed in the Yangtze River Basin,and the precipitation anomaly expands to the northeast.The increasing precipitation in Yangtze River Basin is caused by the strong and northward western Pacific subtropical high.The meeting of its southwest wind the cold air from the middle and high latitudes leads to the precipitation.(3)There are two main influencing factors act on the eastward extension time.When the heating sources over the Tibetan is strong in February,a cyclone circulation forms in the south of the Tibetan and southerly anomaly appears from the southeast of Tibetan to the west Pacific,which contributes to the occurrence of the eastward extension of the year-round southerly.Furthermore,the thermal anomaly of ocean also influences the year-round southerly eastward extension,the sea surface temperature(SST)anomaly in Ni?o3.4 are negatively correlated with the eastward expansion time series.The year-round southerly eastward extends earlier when El Ni?o events appear.Moreover,the year-round southerlyregion extends to the east more obviously during the CP El Ni?o years.The tripolar of SST anomaly in south India Ocean would motivate a wave train from south India Ocean,which enhances the flow around and southerly anomaly,conducing to the enhancement and eastward extension of the year-round southerly.(4)The model members in CMIP5 are poor in simulating the eastward expansion of the south wind.Otherwise,for simulating the variation of the south wind intensity,the BCC-CSM1.1,GFDL-CM3 and MIROC5 are do the best.Nevertheless,there is obvious inconsistency in their predictions of the variable of the south wind under global warming.BCC-CSM1.1 and GFDL-CM3 shows that the south wind will weaken in Autumn,and the trend will be aggravated with the increase of temperature threshold;while MIROC5 shows a opposite result.The reason is that the warming range over Tibetan Plateau are overestimated in MIROC5.