Numerical simulation of a heavy rainfall event in China during July 1998

A detailed analysis associated with this case has been carried out (Zhao et al., 2001). In order to conduct further research on the meso-beta scale system, which is the directly influencing system, the heavy rainfall that occurred in Wuhan (Station no.: 57494) and Huangshi (Station no.: 58407), Hubei Province during July 1998 are simulated using higher resolution and more complete initial data, after the large scale fields and rainfall areas have been simulated successfully. The simulation results indicate that there are meso-beta scale weather systems which developed and dissipated near Wuhan and Huangshi during 1800 UTC 20 July to 0600 UTC 21 July and 1800 UTC 21 July to 0600 UTC 22 July in 1998, respectively. The life cycle of the meso-scale system is about 12 hours and its horizontal scale is from 100 to 200 km. These are characteristic of a typical meso-beta scale system. By analyzing the vertical section of wind field and other physical variables during the mentioned-above two periods, it is found that horizontal convergence, ascending motion and positive vorticity of the middle and lower troposphere are strengthened during the heavy rainfall periods near the above mentioned two places. In addition, the wind disturbance in middle and lower troposphere may be a possible triggering mechanism for the occurrence of the meso-beta weather system. A budget analysis of the meso-scale system indicates that the sources of moisture and positive vorticity are different during the different stages of the meso-scale systems. Finally, a three dimensional conceptual model of the meso-beta scale systems causing the sudden heavy rainfall in Wuhan and Huangshi is suggested.