The Analysis on the Features of the Atmospheric Circulation in Preceding Winters for the Summer Drought and Flooding in the Yangtze and Huaihe River Valley

Based on the annual variation of the rainfall departure percentage in summer in the lower-middle reaches of the Yangtze River and the Huaihe River valley, 7 cases for the abnormal drought and flooding summers (the drought years: 1981, 1984, 1985; the flooding years: 1980, 1982, 1983, 1987) are selected, First we analyse the general circula-tion characteristics of the summer drought and flooding, and then the evolution processes of the general circulation patterns from preceding winters to summers are studied. It is found that during the two kinds of preceding winters for the drought and flooding summer, not only the general circulation patterns in the high-mid latitudes, the local Hadley cells in East Asia but also the activities of the cold surge in the lower latitude are different obviously. Spring, especially April, is the turning period of the general circulation in preceding winter for the drought or flooding sum-mer evolution towards opposite direction. Hereafter, the drought or flooding circulation pattern is established and developed.