湖北省夏季不同阶段强降水及其大气低频特征

摘要

提利用1961—2014年湖北省68站逐日降水资料和美国国家海洋和大气管理局环流资料，对比分析了湖北省夏季梅雨期和盛夏期低频强降水事件的基本特征、大气环流形势和低频信号传播特征。结果表明：（1）湖北省夏季降水存在显著的准双周低频周期。（2）相较于盛夏期，梅雨期低频强降水事件次数多，强度强。（3）梅雨期和盛夏期低频强降水事件发生期间的环流形势有着显著的差异。梅雨期，对流层中层东亚沿岸为南北向的波列分布，低层受强索马里越赤道气流和副热带高压外围西南气流共同影响，水汽条件好，东亚存在鞍型场，流场变形，利于形成中尺度气旋系统；盛夏期，对流层中层为欧亚波列分布，低层索马里越赤道气流弱，主要受副热带高压外围水汽输送的影响，日本海以西地区有一异常气旋，其西侧的偏北气流与暖湿气流在30°N附近交汇维持。（4）在强降水事件发生前后，对流层低层的低频正涡度传播特征有较大差异，在梅雨期表现为驻波特征，盛夏期传播更为明显，表现为向西、向南向北传播。%Anstract:By using the daily precipitation data of 68 stations in Hubei and NCEP/NCAR circulation reanal-ysis data,the characteristics of the heavy rain events and low-frequency atmospheric features between the Meiyu and midsummer periods are studied.The results indicate that the quasi-biweekly oscillation of pre-cipitation exists obviously in summer over Hubei.Compared with the rains in the midsummer period,low-frequency heavy rain events in the Meiyu period are seen more often with stronger intensities.There are significant differences of low-frequency heavy rain events between the Meiyu and midsummer period.Dur-ing Meiyu period,circulations show the distribution of north-south wave trains above the East Asia Lit-toral in the mid-level troposphere.The combined impact of strong Somali cross-equatorial flow and south-west air current around subtropical high contribute to the abudant water vapor.The saddle-type field of circulations in East Asia and transformed flow field are beneficial to the formation of mesoscale cyclonic systems.In the midsummer period,however,circulations distribute in the pattern of Eurasian wave trains in middle troposphere.In lower troposphere,water vapor comes from subtropical peripheral with the weak Somali cross-equatorial flow.The north air streams from the west of the cyclone to the west of Japan Sea and the south warm-wet air streams from the periphery of subtropical high get intersected and maintained over 30°N.Before and after the heavy rain events,there are obvious differences of the low-frequency posi-tive vorticity propagation in low troposphere.The low-frequency positive vorticity during the Meiyu period shows the characteristics of standing wave while in the midsummer,it propagates westward,southward and northward obviously.