一次特大暴雨中尺度系统结构特征和机理分析

为了研究“04.6”湖南特大暴雨过程的发生发展机理,在天气分析的基础上,利用非静力中尺度模式MM 5-V 3.6对本次过程进行了数值模拟。结果表明:高分辨中尺度模式MM 5可以较好地模拟中尺度低涡切变线的发生和发展。模拟结果显示,中尺度低涡发展过程中,不断有扰动在低涡前部发展,并激发出强烈的中尺度对流系统M CS(m esoscale convective system)。暴雨区上空具有同向双圈垂直环流结构特征,使中尺度对流系统更加组织化。根据湿位涡守恒和倾斜位涡发展理论分析了暴雨和M CS形成和发展的原因。对流不稳定和条件对称不稳定的建立以及对流有效位能的集中释放是此次特大暴雨产生和持续发展的重要条件。

Mechanism of strong rainstorm and structure of mesoscale system

Based on the synoptic analysis of the strong rainstorm of Hunan on June 23,2004, the nonhydrostatic version of mesoscale numerical model MM5-V3.6 was used to simulate this case.The results indicate that high resolution model MM5 can preferably simulate the occurrence and development of the low mesovortex with shear line,and that there are many disturbances in front of the low vortex and the strong mesoscale convective system inspired with the development of the low vortex.Over the rainstorm area,the vertical double-circulation causes the mesoscale convective system to become much more systematic.The development of the rainstorm and MCS were investigated with moist potential vorticity principle and slantwise vorticity development theory.The establishment of convective instability and conditional symmetry instability,and the centralized release of convective available potential energy(CAPE) are important conditions of the occurrence and development in this rainstorm.