Characteristics of the circulation during the catastrophic flood period over China in 1998

The characteristics of the general atmospheric circulation during the catas trophic flood period over Yangtze River Valley in 1998 are discussed. There are two patterns of precipitation distribution: the pattern of floodwater over Yangtze and Precipitation more than normal in the whole country, and t he pattern of floodwater over Yangtze and precipitation less than normal in its north and south. The 500hPa circulation characteristics of the two pat terns are studied. The results show that there are obvious difference of th e 500hPa circulation in the northern hemisphere. The establishment of Okhot sk Sea Blocking High is a major factor in causing the floodwater over Yangt ze valley and the intensity of South China Sea High is a important factor o f forming the pattern of floodwater over Yangtze and precipitation more tha n normal in the whole country.