利用常规观测资料、NCEP再分析资料、多普勒天气雷达资料及数值模拟结果，对2012年8月21日南昌市的一次大暴雨过程进行了数值模拟和诊断分析。结果表明，整层偏南暖湿气流为此次暴雨提供了充分的水汽和不稳定能量。地面冷空气的侵入，促使南昌上空中低层不稳定能量释放，是产生此次强对流过程的直接触发机制。影响南昌市的强雷暴回波有较明显的强回波低质心特征，降水效率较高，加之较长的持续时间，导致此次短时暴雨的重要原因。各物理量诊断分析表明，暴雨区强辐合上升运动，中低层大气强不稳定性层结使得上下层大气物质交换强烈，且低层辐合高层辐散造成的抽吸作用集中在一个纬度左右非常窄的地区，导致此次暴雨过程局地性强。暴雨区上空螺旋度分布呈“下正上负”的垂直结构，螺旋度正的大值区对应强降水中心。%Using conventional observation data, NCEP reanalysis data, Doppler weather radar data and numerical simulation results, a short-term heavy rainstorm process occurred on August 21, 2012 in Nanchang was diagnostically analyzed. The results show that the whole layer of warm southerly provided plenteous moisture condition and unstable energy for this rainstorm. The invasion of ground cold air, which led to the release of unstable energy, was the direct trigger mechanism for this strong convective process. The radar echo presented a low-quality heart,which caused efficient precipitation and a longer duration. The diagnostic analyses of each physical quantities showed that the strong convergent ascending movement, strong instable stratification in middle and lower layer and the narrow pumping zone by the lower level convergence-high level divergence induced the local heavy rainstorm process. The helicity over the rainstorm region presented a“high-positive and low-negative”structure and the positive maximum helicity correspond to the heavy rainfall center.
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