A Diagnostic Study of Mesoscale Lows (Disturbances) on Meiyu Front and Associated Heavy Rainfall
引发梅雨锋暴雨的频发型中尺度低压(扰动)的诊断研究

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).