Diagnostic Analysis of Potential Vorticity and Vertical Motion in a Torrential Rainfall Event Associated with Dry Intrusion in the Summer of 2020
JIN Chenyi
ZHANG Guanshun
LONG Yuqing
Abstract：In the summer of 2020,frequent rainstorm events hit the Yangtze River Basin(YRB)in China.These rainstorms were closely related to the southward intrusion of high-value potential vorticity(PV)at the mid-to-high latitudes.Based on observational data and ERA5 reanalysis data,the dynamic mechanism of a rainstorm process in early July 2020 was investigated through PV diagnosis,vertical velocity decomposition,and backward trajectory tracking simulation.The results show that the southward PV intrusion,which was often coupled with dry intrusion processes,was related to the amplification of trough and ridge systems,as well as the PV advection caused by their convergence/divergence processes in the upper troposphere.Dynamically,the high-value PV intrusion in the upper troposphere and the PV development in the lower level jointly resulted in the tilting of isentropic surfaces,which was reflected in the change of vertical velocity component caused by the displacement of isentropic surfaces.The development of the vertical velocity component in relation to descending motion was attributed to the upper-level northerlies gliding along the isentropic surfaces,leading to a dry intrusion process.On the other hand,the southerlies continued to move along the sloping isentropic surfaces,persistently transporting water vapor upward.In such a manner,the condensation process accompanying the water vapor uplift further led to the development of the vertical velocity component related to non-diabatic heating,thereby reinforcing the vertical motion and triggering convection.After the onset of the convective motion,strong rainfall caused significant latent heat release in the middle and lower troposphere,which led to PV due to its vertical distribution that increased with height in the lower level.The enhanced vortices further promoted rainfall development by affecting the isentropic surface structure and vertical motion.It is the positive feedback mechanism among the PV,strong rainfall,and the three vertical motion components that maintained and promoted the rainstorm over the YRB.
Keywords：potential vorticityrainstormdry intrusionvertical motionbackward trajectory tracking
Publication Date：2024-06-28
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：14( 411-424 )