Study on a mesoscale convective vortex causing heavy rainfall during the mei-yu season in 2003

The strong heavy rainfall on 3-5 July 2003 causing the severe flooding in Huaihe River basin (HRB), China is studied. It is noted that there are sometimes mesoscale convective vortex (MCV) in East Asia during the mei-yu season. Simulation results from the ARPS (Advanced Regional Prediction) data analysis system (ADAS) and WRF model were used to study the development of the mesoscale convective system (MCS) and mesoscale convective vortex (MCV). It is confirmed that the MCV formed during the development of a previous severe MCS. A closed vortex circulation can be found below 600 hPa with a vorticity maximum in the middle troposphere. The evolution process of the MCV can be divided into three stages: initiation, maturation, and dissipation. During the mature stage of the MCV, a downdraft occurred in the center of the MCV and new convection developed in southeast of the MCV. The convergence and the tilting in the lower troposphere convergence and vertical advection in the middle troposphere were the main vorticity sources in the MCV initiation stage. Finally, a conceptual model between the mei-yu front and the embedded MCS and MCV is proposed. The mei-yu front was the background condition for the development of the MCS and MCV. A low level jet (LLJ) transported moisture and the weak cold air invasion via a trough aloft in the middle troposphere and triggering the severe convection. Furthermore, the intensified jet was able to result in the initiation of new secondary areas of convection in the eastern part of the MCV.