Effects Of Heating Over Tibetan Plateau On The Persistent Heavy Rainfall Events In Southern China During June2010

Persistent heavy rainfall occurs over southern China during June2010, with a magnitude being comparable to June2008and exceeding the other recent years. The June of2010is characterized by frequent occurrences of low-value systems in the middle-and-low troposphere from Qinghai-Tibet Plateau to the lower reaches of Yangtze River, the significantly intensified West Pacific subtropical high (WPH), leading to more northward located low-level anomalous wind convergence and rain bands compared to June of2008.Analyzing the four successive persistent heavy rainfall events over southern China during14-24June2010, it is found that the water vapor mainly come from the South China Sea and the Bay of Bengal. During each of the events, positive relative vorticity propagates eastward from the eastern Tibetan Plateau corresponding to the frequent occurrences of the eastward-moving shallow troughs at500hPa, the quasi-east-west oriented shear lines and eastward-moving vortices in the lower troposphere. During the first three precipitation events, the South Asian high gradually intensifies, expands and shifts towards the Tibetan plateau; in the middle troposphere, the middle-and-high-latitude trough and ridge strengthen, the West Pacific subtropical high (WPH) is very strong. In the fourth event, the South Asia high substantially weakens and shrinks, the mid-level trough and ridge moves eastward, WPH retreats eastward and southward, and the precipitation gradually stops. Moreover, an ensemble of convection-permitting simulations (CTL) is carried out using the WRF model for these rainfall events which successfully reproduces the observed evolutions of precipitation and weather systems. Another ensemble of simulations (SEN) with the surface albedo over the TP and its southern slope being changed artificially to one, i.e., the surface does not absorb any solar heating, otherwise it is identical to CTL, is also performed. Comparison between CTL and SEN suggests that the surface sensible heating of TP in CTL significantly effects the temperature distributions over the plateau and its surroundings, and the thermal wind adjustment consequently changes atmospheric circulations and properties of the synoptic systems, which significantly intensifies the precipitation over southern China. Specifically, at200hPa, anticyclonic and cyclonic anomalies are formed over the western and eastern plateau, respectively, which enhances the southward cold air intrusion along the eastern TP and intensifies the divergence over southern China; At500hPa, the ridge over the northern plateau and the trough over eastern China are strengthened, the southwesterly flows along the northwestern side of the subtropical high are intensified, and the positive vorticity propagation from the plateau to its downstream are also enhanced significantly; At850hPa, the low-pressure vortices strongly develop and move eastward while the southwesterly low-level jet over southern China is intensified in CTL, leading to stronger water vapor convergence and upward motion over the precipitation region.