NUMERICAL STUDY OF THE EVOLUTION MECHANISM OF MESO β SCALE CONVECTIVE SYSTEM ALONG THE MEI-YU FRONT

On 18-19 June 2002, a mesoscale convective system developed in Hubei Province along the Meiyu front. The synoptic situation showed that the mesoscale convective system was influence by the shear line at 850 hPa. From the Tbb data, the evolution of the convective cloud clusters was very clear. It was obvious, during this event, the mesoscale convective system split into two mesoβ scale convective systems when it moved toward the northeast. To understand the evolution mechanism of the MCS, numerical simulations for this event was performed using mesoscale model (MM5). The model successfully captured the evolution of the MCS, including the vertical structure. Due to the divergence in the high level and the convergence in the low level, the MCS was strengthened. In addition, the divergence in the high level was the cause of the movement of the MCS. And influenced by the orography, when the MCS moved to the mountain, it separated into parts. From the sensitivity experiment of the mountain, the orography was shown to be important for the splitting of the MCS. The existence of the mountain not only contributed the lowlevel convergence and enhanced upslope winds, but also made the MCS separated and to dissipate. The results indicated the mountain wave was produced when the air current passed by the orography. Then, because of the reduction of moist air in the mid-level and the downdraft of the mountain wave, the meso β scale convective systems were weakened. According to the analysis, a conceptual evolution model of the MCS along the Mei-yu front has been achieved.