Numerical simulation on mesoscale convective system along Mei-Yu front in Southern China

A mesoscale convective system (MCS) was generated over the South China Sea at around 115 degreesE, 21 degreesN on 0000 UTC 7 June 1998. Riding along t he Mei-Yu front, the system moved through the Taiwan Strait and finally hit the southern part of the Taiwan Island, produced over 300 mm of rainfall o ver parts of Taiwan in the next 24 hours. It was found that the Penn State- NCAR Mesoscale Model Version 5 (MM5) did quite well in simulating the evolu tion of the MCS. Diagnostic studies on the mesoscale structure of MCS, mois ture concentration process and the momentum budget were based on the model output. The concept model of the MCS in the mature phase can be concluded a s the following: At the 850 hPa level, the mesoscale low level jet (mLLJ) w as found to the southwest of the MCS, which was also associated with a meso scale low generated by convection, the mesoscale upper level jet (mULJ) was found due east of the MCS (and an upper-level mesoscale high) at the 300 h Pa level. Horizontal advection of momentum acted to accelerate the exit of the mLLJ but decelerate the entrance of the mLLJ where the pressure gradien t force acted to compensate this lost and maintain its strength. For mainte nance of the mULJ, vertical advection of momentum and the pressure gradient force were both found to be important.