一次华南持续性暴雨的动力诊断分析和数值模拟

Dynamic diagnosis and numerical simulation of a persistent torrential rain case in South China

利用倾斜涡度发展(slantwise vorticity development,SVD)理论,对2008年6月中旬华南地区持续性暴雨进行了动力学机制的诊断分析,讨论了低空急流(low level jet,LLJ)在低涡发展过程中起的作用,同时利用MM5数值模式对暴雨过程进行了验证并对模拟结果进行了进一步分析。结果表明,高原低涡的发展是前期广西地区降水的主要动力因素,由于湿等熵面相对地形倾斜,且气块沿等熵面有相对运动,同时满足热力学参数CM<0的条件,使得SVD发生作用,导致低涡移出高原后得到进一步发展;而LLJ的增强改变了大气斜压性,是后期低涡继续东移发展,并造成广东地区持续性暴雨的重要原因。数值模拟控制试验结果很好地反映了这次低涡降水的发展过程。敏感性试验结果初步表明,LLJ改变了低层大气稳定度和风的垂直切变,即大气斜压性增强,从而促进了中尺度低涡的进一步发展。

Based on slantwise vorticity development（SVD） theory, the possible dynamical mechanism of a persistent torrential rain which occurred in mid-June of 2008 was analyzed, and the role of low lev-el jet （LLJ） in vorticity development was discussed. Meanwhile, several numerical simulations were performed to testify the rainstorm process based on MM5 and the results were further analyzed. The re-sults indicate that：the development of low vortex from Tibetan Plateau was the primary cause for the precipitation in Guangxi and Guangdong at early stage. SVD took effect while moist isentropic surface tended to slope and air particles had relative motions along isentropic surface. With certain condition （Cu 〈 0 ）, the vorticity got a further development afterwards. Moreover, the enhancement of LLJ changed the atmospheric baroclinity and caused the vorticity to develop and move eastward, which was the main cause for the persistent torrential rain in Guangdong. The results of simulation control test well revealed the development process of the vortex and precipitation. The result of sensitive test showed that LLJ changed the stability of low level atmosphere and vertical shear of the wind, which meant that the baroclinity of the atmosphere was increasing. It thus made the mesoscale vortex develoo further.