引发梅雨锋暴雨的频发型中尺度低压(扰动)的诊断研究

利用再分析资料及加密观测资料,对1999年6月下旬有利大尺度环境条件下长江中下游地区梅雨锋上频发的5个中尺度低压(扰动)进行了诊断研究.由合成分析得到了长江中下游地区中尺度低压(扰动)的基本特征(共性);依其特征将之归纳为两种类型;之后选择两个典型个例分析了它们各自发生发展过程中特征的异同(个性).分析结果揭示了梅雨锋中尺度低压(扰动)的动力和热力结构特征、暴雨过程中对流活动的详细过程及典型雨团的路径和生命史.此外,高山站每小时的风记录等信息反映出低空西南急流和其上大风速中心同中尺度低压(扰动)及暴雨发生演变过程有密切关系.高空急流对中尺度低压(扰动)的发展及暴雨有明显的作用,有无高空西风急流与低空急流的耦合似乎是未来发展与不发展中尺度低压(扰动)之间重要的动力学区别之一.

A Diagnostic Study of Mesoscale Lows (Disturbances) on Meiyu Front and Associated Heavy Rainfall

By utilizing reanalysis and intensive observation data, characteristics of mesoscale lows (disturbances) are studied, which occurred on Meiyu front over the middle and lower reaches of the Yangtze River during the last ten-day of June in 1999. It is confirmed that there existed at least five mesoscale lows (disturbances), which were the direct makers of heavy rainfall, occurring during that period. They could be divided into two groups according to their characteristics. The common characteristics of mesoscale lows (disturbances) over the middle and lower reaches of the Yangtze River are obtained by means of compositive analysis. Then two typical cases are selected and analyzed. The dynamical and thermodynamical structures of mesoscale lows (disturbances) are investigated. The detailed evolution of convection, track and lifecycle of typical convection are also revealed. In addition, wind data of Huangshan station and other information show that southwest low-level jet and wind streak on it are related closely with the process of mesoscale lows (disturbances) and associated heavy rainfall. The coupling between the westerly upper-level jet and the southwest low-level jet seems to be one of main dynamical factors that cause the evident development of mesoscale low (disturbance).