Analysis on mesoscale characteristics of two vortex rainstorms in the Huanghe-Huaihe regions

Observational data from surface automatic weather station (AWS), satellite, Doppler weather radar and NCEP reanalysis were used to analyze the environmental conditions and the evolution of mesoscale systems for two severe precipitation events (respectively referred to as "7.17" case and "7.18" case) originated by a vortex rainstorm in the Huanghe-Huaihe regions during July 17-19, 2010. The results showed that (1) the two cases both occurred under sufficient water vapor transport, abundant unstable energy, strong convergence upward motion and other favorable environmental conditions. There are more favorable thermal conditions and severer precipitation but smaller areal coverage in the "7.17" case, while there are more favorable dynamic conditions and broader severe precipitation area but lower rainfall intensity in the "7.18" case. (2) The accumulated rainstorm area in the "7.17" case is located on both sides of the movement path with 30-80 km about cyclone center, while that in the "7.18" case is 70-100 km. (3) The mesoscale rain clusters (bands) and the short-time heavy rainfall occur mainly around the mesoscale cyclones on the ground, and there are different heavy precipitation areas during their different activity stages. (4) It is seen in the satellite images that heavy precipitation in both cases is generated by convective clouds moving from southwest to northeast, whose TBB is as low as 210-220 K. (5) It can be found in the radar echo charts that in the "7.17" case the vortex is more evident while in the "7.18" case the echo band induced by cold and warm shear is. During the two events, the mesoscale rain band corresponds to the spiral echo belt with 43 dBz or greater, but the short-time heavy rainfall corresponds to strong echo with 48 dBz or greater in the spiral rain band.