The Evolution and Structure of the Long-Lived MCV Along the Mei-Yu Front

The evolution and structure of the MCV (mesoscale convective vortex) and its corresponding convection along typical Mei-yu front during 1-10 July 2007 is explored within the diurnal cycle boundary forcing experiment via 30-day integration of the Weather Research and Forecasting model. Four stages are divided in the main evolution of the MCV and its convection. The first stage is the formation of MCV (V1) and its convection (C1) appearing in the morning to early afternoon. The eastward extending vorticity and convection from Sichuan Basin in the early evening triggers the immediate enhanced lee-side localized vortex below 700 hPa east of the second step terrain and the convection is almost consistent with vorticity maximum. The second stage is the uncoupling of C1/V1 from the local afternoon to early evening. The convection decreases overall and shifts to the east-southeast side of the vorticity maximum and the vortex covers more broadening area, due to the suppression of the downdraft of day-time MPS and the intensified steering wind speed in the middle levels, the upward motion shifts over the west side of the MCV center. While in the evening to early morning, the updraft branch of the nocturnal MPS circulation and the enhanced nocturnal low level jet favors the new convection (C2) in the southeast side of MCV and the diabatic heating from water vapor condensation in the low levels triggers the new MCV(V2), which is referred as the formation stage of C2/V2. Then, the occlusion stage of C2/V2 appears in the next early morning before significant solar heating. The new MCV rolls into a sub synoptic cyclone with signs of occlusion; potent convection within all sectors of the vorticity maximum, as well as stretches the convergence line to the southwest side that has a separate vorticity and convection maximum.