| Viet Nam lies in South-East Asia, belonging to tropical and subtropical climate region. According to geographical characteristics, it is divided into three parts. The characters of precipitation distribution of the three parts are different because of difference of climate conditions. In a word, the precipitation of the south and middle parts of Viet Nam concentrate in the autumn season, while the rainfall of the North part mainly occurs in summer. The intensity and the anomaly of the seasonal variation of rainfall often bring flood or drought, which can do great damages to local people's living and the development of economy. At the same time, the tropic cyclones are also one of the main factors bringing disasters to Viet Nam, it can cause severely strong wind and storms that can make agriculture, fishing and industry production suffer a great lot of losing. Thereby, it is very necessary to make a deep and full understanding to the summer and autumn precipitation variation characters of Viet Nam and the climatic characters of tropical circles landing Viet Nam, and to find out the synchronous and anti-chronic factors that have close relationships with the characters mentioned above so as to provide some theoretic evidences for short range prediction of Viet Nam rainfall and the climatic forecasting of the frequency of the tropical cyclone that will land Viet Nam which have important meaning to the stable and continuous development of the national economy.1. Viet Nam precipitation characterViet Nam can be divided into three regions, there are different characters in different regions: In the south and middle regions, rainfall mainly concentrate in autumn, while in the north region, rainfall mainly occurs in summer.2. The precipitation character of the North part of Viet Nam and its relation to the atmospheric circle.There is a clear relation between Summer rainfall in north part of VietNam and pre-Spring 100hPa gee-potential height field, the key region is north part of the North Pacific; There is also an obvious relation between Summer rainfall and pre-Spring 500hPa geo-potential height field, the key regions is north part of the North Pacific, Greenland and south part of the South Pacific.3. The precipitation character of the Middle part of Viet Nam and its relation to the atmospheric circle.The autumn precipitation of the middle part of Viet Nam has obvious variations in inter-annual and inter-decade scale with clearly quasi 6a,10a,15a period; In heavy rainfall years, there are a positive anomaly over the north-west Pacific and a negative anomaly over Japan; While in deficient rainfall years, the anomaly distribution is on the contrary;4.The precipitation character of the South part of Viet Nam and its relation to the atmospheric circle.The research finds that the rainfall of the south part of VietNam usually concentrates in the autumn every year and a clear difference of atmosphere condition exists between that of flood and drought years. There is a distinct relation between autumn rainfall of south part of VietNam and zonal component of wind field, especially the 850hPa zonal component of wind over the tropical Pacific.5. The frequency character of tropical cyclone landing Viet Nam, and its relation to rainfall in Vietnam.In summer, the variation of frequency of the landing tropical cyclone is great, the biggest is five, the smallest is only one. Seeing from the nine-year smoothing curve, there is obvious variation in inter-decade scale for frequency of landing tropical cyclone in summer.In autumn, the variation of frequency of the landing tropical cyclone is also great, the biggest is nine, the smallest is only zero. Seeing from the nine-year smoothing curve, there is obvious variation in inter-decade scale for frequency of landing tropical cyclone in summer.There is a clear positive relationship between frequency of landing tropical cyclone in summer and summer rainfall of some north city and middle part of Vietnam. That is to say, there will probably be more rai...
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