Diagnostic Analysis of Moist Potential Vorticity for Southwest Vortex Heavy Rain

With the NCEP/NCAR 1°×1° data the moist potential vorticity (MPV) anomaly of a highly intensive precipitation event in the central and eastern part of China from 25~26 May 2013 is diagnosed.The results showed that:(1) When heavy rain occurred,the distribution of MPV barotropic part was‘-+’ from low to high level.The evolution of low value centrer of MPV baroclinic showed the baroclinicity played an important role when a heavy rain occurred.(2) The process of the rainstorm divided into two stages,in the first stage,the rainfall was high convectiom feature because of the strong vertical wind shear;in the second stage,the rainfall was widely distributed and had long duration feature because of the atmospheric baroclinicity.(3) The dry cold air spread downward from the upper troposphere along the isentropic onto the negative MPV in low level,thus increased the convective instability,the development of the vertical motion maked the lower layer vapor lifting,latent heat release was beneficial to the maintenance and development of the low vortex.