Water Vapor Transport Simulation, Eastern China Summer Rain Belt Change The Diagnosis

By using observational and NCEP re-analyses data, we diagnose the feature of vapor flux that affects rain belt changes in Eastern China, the results show: The feature of vapor flux corresponding to 1st type of rain is that vapor flux anomalies from Northern China, mid-latitude land and mid-latitude Western Pacific(WP) converge at Northern China and lead to rain anomaly in this area; and that corresponding to 2nd type of rain is that vapor flux anomalies converge in Jianghuai river; and that corresponding to 3rd type of rain is that vapor flux anomalies form North - East and West-South converge in Yangtze river. Further analyses reveal that increase of northward vapor flux anomaly in Southern China Sea(SCS) will raise rain in Southern China and Jianghuai river; and also increase of northward vapor flux anomaly in Bengal bay will increase rain in Southern China and decrease rain in Jianghuai river; In May and June, increase of eastward vapor flux in tropical WP will raise rain in Southern China, while in July it will raise rain in JiangHuai river, and in August it will raise rain in Jianghuai river and Northern China; In May, increase of northward vapor flux in mid-latitude WP will raise rain in Jianghuai river, and in June that will raise rain in Northern China, while increase of west-southern vapor flux will raise rain in Jianghuai river and lessen rain in Southern China. In July increase of eastward vapor flux will raise rain in Jianghuai river and increase of southward vapor flux will raise rain in Northern China, while northward vapor flux will raise rain in Jianghuai river. In August, increase of eastward vapor flux will raise rain in Jianghuai river.In order to check the simulation ability of regional climate model-RegCM3, we use the model to simulate summer rain in Eastern China in 1998, the result shows that the model can well simulate monthly changes of rain from May to August 1998, it also revealed the evolution of subtropical high, monsoon and propagation of two intral-seasonal events. So, the model can be applied to the study of summer rain in Eastern China.Using the mean NCEP re-analysed data during 1987 and 2001 as initial field, we use RegCM3 to do some sensitive experiments by changing vapor flux in SCS, Bengal bay, tropical WP and mid-latitude WP, the result shows: Increase of vapor flux in SCS will raise rain in Southern China, and vise versa; Increase of vapor flux in Bengal bay will increase rain in Southern China, and decrease rain in Jinaghuai river, and vise versa; The influence of vapor changes on rain is most eminent in August, when vapor flux increase, rain in Jianghuai river will decrease and rain in Southern China will increase. In July, the increase of vapor flux will raise rain in Jianghuai river. It is complex in June when the influence of vapor flux change is not clear at this time; Influence of vapor flux changes in tropical WP on rain in Eastern China is more complex, in June, increase and decrease of vaporflux will decrease rain in Southern China and increase rain in Jianghuai river, while in August it will raise rain in Southern China and decrease rain in Jianghuai river, in July, increase of vapor flux will raise rain in Southern China and decrease rain in upriver of Yangtze.