| The area of Northwest China is about 3.0 108km2, which is about one third of the whole China's area, and Northwest China is abundant with national resource, which is very important to the persistent development of the society and economic. As we all know, Northwest China is far from the Pacific Ocean and Atlantic Ocean, so it is difficult for the vapor coming form these oceans in summer to arrive this area. For this reason the precipitation is always very little, and the drought is the prominent character of the area in summer. The drought climate has bad effect on the national resource's exploitation and use. It is good for the Northwest China's development if we can grasp the variety of the drought.In this paper, we present a study on the characteristic of precipitation over Northeast side of Tibetan Plateau, in which the variation of the precipitation is very enormous. Five drought years and flood years of each summer month are selected by using precipitation data, and the characteristics of drought or flood in the whole atmosphere are studied.The main results show as follow:1.Drought flow pattern and flood flow pattern are the whole atmosphere's character. Monthly average composite potential geographical high in nine levels(850hPa, 700hPa, 600hPa, 500hPa, 200hPa, 100hPa, 70hPa, 50hPa, 30hPa) are studied, and we also study the composite potential geographical high's similarity between 500hPa and other eight levels. All the studies show that the drought flow pattern "west positive east negative" and flood flow pattern "west negative east positive" not only exist in 500hPa presented in 80s last century, but also exist in other levels. So the drought flow pattern or flood flow pattern is the characteristic of whole atmosphere.2. East Asia north wind indexes in drought years are larger than in flood years on each levels. In this paper, we calculate the East Asia north wind index on different levels according the north wind index presented by Bai Zhao-ye and Xu Guo-chang. The results show that East Asia north wind index in drought years is larger than that in flood years.3. There exists distinct statistical relationship between precipitation of each summer month and prophase atmosphere general circulation introposphere and low stratosphere. June's precipitation has good relation not only to March's potential geographical high on 500hPa, but also to January's potential geographical high on 70hPa and 50hPa, July's precipitation has distinct statistical relation not only to December's potential geographical high of last year on 500hPa, but also to June's potential geographical high on 70hPa and 50hPa, and August's precipitation are good correlation with the variation of February's potential geographical high on 500hPa and March's on 70hPa and 50hPa.4. sections of drought and flood years in each summer month over Northeast side of Tibetan plateau show that curves are 's' . The vertical velocity in low troposphere is larger than high troposphere, and vertical velocity in flood year is also larger than that in drought year. The vertical velocity on different levels show that there exists distinct sinking motion from midlevel to uplevel of troposphere in drought years and updraft in whole atmosphere in flood years.5. The divergence in mid- and low-level and the convergence in up-level of troposphere are strong in drought years over Northeast of Tibetan Plateau, which cause the sinking motion stronger than usual in the whole atmosphere. But in flood years, the convergences in mid- and low-level of troposphere are strong. Divergence departure in 200hPa is positive, so the pumping cause the updraft stronger. As we all know, the updraft is better to the rain.6. We also analyse the relative vorticity departure's characteristic. We found that there are always negative vorticity departure in drought years over Northeast side of the Tibetan Plateau, which means there exist anticyclone and there are little precipitation. On the contrary, there are positive vorticity departure, and t... |
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