Typhoon Activity Effect On Precipitation Over North China During Flood Season

The characteristic of tropical cyclone activity is hotspot internation TC study filed on the global climate warming background. TC rainfall is a important part of typhoon activity.Using the NCEP/NCAR monthly mean reanalysis index of subtropical high and Asia polar vortex and rainfall and typhoon precipitation of 1957-2002 over North Cniha in rainy season, are employed to diagnose and analyze the typhoon activity effect on flood season rainfall the feature of spatial and temporal of typhoon rainfall and it contribution to flood season precipitation, and the different characteristics of circulation:1. Rainfall of North-China is displaying decreases trend.Rainfall of North-China and the frequency of landing typhoon are positively(negatively) correlated in most parts of central and eastern(southern)of North-China.Not only the feature of sea level pressure and 850hpa streamline anomaly field but also the characteristic of 500hpa heigh anomaly field and cold air track circulation are similar to each other during years of more(less) active typhoon and more(less) rainfall over the central and east areas of North-China.2. Typhoon number in flood season is displaying decrease in the 46 years,it has para-period of 11,and,2 years. 1967 is the catastrophe point at which the frequency of typhoon begins a downward tendency.Effects on Northern China,rainfall typhoon lands at two key areas of Coastal Shangdong and Hualian-Yilan of Taiwan.3. Typhoon rainfalling of flood season is gradually falling in the past 46 years and consistent with a para-period 2.-3 years.The typhoon rainfall decrease from south-east to north-west,the relief make effect more complication.4. Not only overall typhoon rainfall contribution rate and July displaying decrsaes trend in past 46 years but August is increase. The high value of rainfall in August covers an area extending to west and north,and is apparently higher than that in July,especially in Henan province of east of Taihang Mount.5. The notable difference of sea level pressure in high(low)-precipitation seasons can be found from Baikal lake to Okhotsk sea, Japanese islands,from South China sea to eastern Philippines;as for the 850hpa zonal (meridional) wind,it differentiates a lot at north-east of North China to north of Korea Peninsula and Japan Sea,East Sea and west Pacific Ocean(east side of Central South Peninsula,eastern of North China,and the center of the Pacific Ocean);in more typhoon rainfall years,there is a teleconnection pattern for 500hpa called Europe/Asia pattern,meanwhile negative EPA might result in less typhoon rainfall.6. Not only summer typhoon rainfall but also monthly typhoon precipitation has well correlation with index of subtropical high and Asia polar vortex,SST.