Feature Analysis of Mesoscale Vortex over Lower Reaches of Yangtze River during Meiyu Period

A procedure designed for sorting mesoscale vortices is used to sort mesoscale vortices over the lower reaches of the Yangtze River during the periods May-July 2006-2009 by using the Japan reanalysis data with high spatial resolution. The results show that mesoscale vortices (disturbances) are often generated in the lower troposphere and planetary boundary layer (PBL). Thus, the mesoscale vortices in this area during the meiyu period could be divided into three types: PBL mesoscale vortices, lower troposphere mesoscale vortices, and lower troposphere-PBL mesoscale vortices. Some of the PBL mesoscale vortices, called PBL mesoscale disturbance vortices (PMDVs), are closely related to rainstorms. Within this group, two distinct patterns of precipitation organization have been identified. One is classified as the MCS-PMDV, which means a mesoscale convection system (MCS) formed before the PMDV. The other is the PMDV-MCS, which is a rainstorm caused by a PMDV. The features of PMDV-MCSs could be identified as follows: a shear line and a low-level jet at 850 hPa, a closed vortex at 925 hPa, and a rainstorm center lying southeast and northeast of the vortex.