Analysis on the Structure of Two Mesoscale Convective Vortices over Yangtze-Huaihe River Basin

The statistics of mesoscale convective vortices (MCVs) occurring in the Yangtze-Huaihe River basin during the Meiyu period of 2003 and 2007 show that MCVs along the Meiyu front were highly active and could have induced severe flooding. Most of the nine MCVs identified during Meiyu period of 2003 and 2007 were formed at 32°N-35°N near the Jiangsu Province. The WRF (Weather Research and Forecasting) model and the ARPS (Advanced Regional Prediction System) data analysis system (ADAS) are employed to simulate two MCVs, in order to study the development and structure of MCVs. It is determined that MCVs form to the north of convection system with a closed vortex circulation maintained below 600 hPa and a vorticity maximum in the middle troposphere. In addition, positive vorticity could reach 300 hPa. The evolution of MCVs can be divided into three stages: Initiation, maturity, and dissipation. During the initiation stage, an updraft can be found in the center of the MCV with neutral stratification. During the mature stage, a downdraft occurs in the center of the MCV, and secondary convections develop southeast region of the MCV. Compared with undeveloped MCVs, developed MCVs may result from the increase of vorticity in the high-level troposphere and more latent heating from secondary convections. Furthermore, the intensified jet is favorable for the triggering and development of new convections of the MCV.