江南南部初夏汛期降水特征Ⅰ:降水集中期及其变化

Characteristics of the early summer rainy season precipitation in southern part of the south of Yangtze River valleyⅠ: Precipitation concentration period and its variation

利用1961-2010年江南地区200个气象站的逐日降水资料，对江南地区初夏降水量的时空分布及其演变特征进行分析。结果表明，在江南南部存在显著的初夏降水集中区，位于27．5-29．5°N的纬向带状区域内；江南南部初夏降水具有季节内相对独立的集中时段，平均发生在6月10-30日。近50a江南南部初夏降水量和暴雨日数没有出现显著的增加或减少趋势性变化，但初夏最长连续降雨日数有弱的减少趋势。江南南部初夏降水具有显著的2～3a和5～6a周期震荡，另外还在1979、1987和2001年出现过3次突变变化。

Floods occured frequently in southern part of the south of Yangtze River valley during early summer from middle May to middle July. Based on the daily precipitation data from 200 stations in the south of Yangtze River valley during 1961-2010, this paper studies the temporal-spatial distributions and evolution characteristics of the early summer precipitation. Results show that, as the transition for the Early Rainy Season in South China to the Meiyu period in the Yangtze-Huaihe River Basin, the East Asia summer monsoon rain belt takes a stay over southern part of the south of Yangtze River valley, which brings about the distinct precipitation concentration period and concentrated region during the early summer. The concentrated region lies between 27.5--29.5°N, around the boundary of Zhejiang, Jiangxi, Fujian and Anhui provinces about. The precipitation concentration period occurs from 10 to 30 June. The early summer precipitation and rainstorm days have not conspicuous increase or decrease trend but the longest continuous rain days are reduced slightly in this region in recent 50 years. The ear- ly summer precipitation has significant 2--3 and 5--6 years periodical oscillations, and there are three abrnpts occured in 1979,1987 and 2001.