【摘要】 重点分析了 １９９９年梅雨季长江中下游地区暴雨集中期大尺度环流特征和主要影响天气系统。认为该期间发生的持续性暴雨是在一种特定的大尺度环流背景下发生的。主要表现为：（１）副高活动有明显的阶段性西进、滞留、东撤．这一特征与中高纬度天气系统的活动密切相关，副高活动直接影响低空急流的水汽输送路径及降水强度；（２）华北高压坝的建立有利于切变线北侧维持偏东风气流，对锋区的稳定起重要作用；（３）高原南侧生成的低涡在沿切变线东移过程中逐渐加强，使梅雨锋中的对流活动加剧，降水加强。更多还原

【Abstract】 This study examines the features about the large-scale circulation and the major systems during the period of the Meiyu rainstorms around middle and low reaches of the Yangtze River in 1999. The features of the persistent rainstorms are considered under a distinctive behavior of the atmospheric circulation as follows: (1) The westward staying and eastward movements of the subtropical high are directly associated with the activities of the synoptic systems around middle latitudes and the strength of the water vapor flux. (2) The development of the ridge around the North china plays a important role in keeping the Meiyu front steady. (3) The vortexes originated from the south of the Tibetan Plateau moves eastward and becomes very strong when arriving over the Yangtze River, which results in a heavy flood on the Meiyu front.更多还原