2011年浙江梅汛期暴雨特征及影响天气系统分析

Analysis on the features and synoptic systems of the rainstorm during Plum Rains Season in 2011 in Zhejiang province

利用NCEP/NCAR再分析资料与气象站网雨量资料,分析2011年浙江梅汛期暴雨特征,并对其影响天气系统进行诊断。结果表明:2011年浙江梅汛期由4次强降水过程组成,雨带较稳定,强降水落区中心基本在钱塘江中上游地区重叠,累计雨量超常,造成钱塘江干流及其各支流流域洪涝频发;南亚高压、副热带高压和中高纬地区"两槽一脊"长时间稳定维持,是浙江梅汛期暴雨产生的大尺度环流背景;与以往梅雨季节来临前副高逐渐西伸北抬到典型梅雨形势的位置后稳定少动不同的是,2011年梅汛期强降水副高最初较偏西,第1次过程后其先东退再西伸北抬后稳定下来,后3次过程梅雨形势非常典型,第1次过程副高位置虽较典型梅雨形势下的偏西,但也产生了非常强的降水;来自北方的干冷空气南侵到锋区时,降水最明显(第3次过程);梅汛期强降水期间,共有三个高空急流核东传,4次过程的强降水先后出现在这三个高空急流入口区的右侧;西南季风北推到30°N附近并稳定维持,决定了2011年浙江梅汛期强降水分布特征。

Using NCEP reanalysis data and rainfall data of automatic weather stations, the features and synoptic systems of rainstorm during Plum Rains Season in 2011 in Zhejiang province are analyzed. The results indicate that the Plum Rains Season in 2011 in Zhejiang province is composed of four severe precipitation processes with stable rain beh, overlapping distribution of severe precipitation in the upper and mid- dle reaches of the Qiantang River and accumulative precipitation more than that in the same period of the past years, which lead to frequent flash floods in the Qiantang River basin and its all tributaries. The stability and continuance of South Asia high, subtropical high over the west Pacific and ＂two trough and one ridge＂ circulation pattern are favorable to the formation of rainstorm during Plum Rains Season in Zhejiang. Different from the stability of subtropical high gradually stretching westwards and moving northwards to the same location as Meiyu period ap- proached in the past, the subtropical high in 2011 is located at west first, and moves eastwards and stretches westwards and moves northwards, and then it is stable after the first severe precipitation process took place; the precipitations from other three processes present a typical circu- lation pattern of Meiyu period, and the subtropical high is westward during the first process, but very severe precipitation emerges in Zhejiang. The precipitation is most significant in the 3rd process when the dry and cold air from the north intruded into front zone. There are three up- per-level jet cores moving eastwards during Plum Rains Season in 2011 in Zhejiang, and the severe precipitation during the four processes emerges on the fight side of entrance region of the three upper-level jets successively. The stability and continuance of southwest monsoon moving northwards close to 30° N determine the distribution of severe precipitation during Plum Rains Season in 2011 in Zhejiang.