Q Vector Analysis of Torrential Rainfall from Meiyu Front Cyclone:A Case Study

Following similar derivation of quasi-geostrophic Q vector (QG), a new Q vector (QN) is constructed in this study. Their di erence is that the geostrophic wind in quasi-geostrophic Q vector is replaced by the wind in QN vector. The diagnostic analysis of QN vector is compared with that of QG vector in the case study of a typical Meiyu front cyclone (MYFC) occurred over Changjiang-Huaihe regions during 56 July 1991.The results show that the QN vector has more diagnostic advantages than QG vector does. Convergence of QN vector at 700 hPa is found to be a good indicator to mimic the horizontal distribution of precipitation. QN vector is further partitioned into four components: QN alst (along-stream stretching), QN curv (curvature), QN shdv (shear advection), and QN crst (cross-stream stretching) in a natural coordinate system with isohypse (PG partitioning). The application of QN PG partitioning in the MYFC torrential rain indicates that PG partitioning of QN can identify dominant physical processes. The horizontal distribution of 2r QN alst is similar to that of 2r QN and mainly accounts for 2r QN during the entire period of Meiyu. The e ects of QN curv on rainfall enhancement fade from the mature stage to decay stage. QN shdv enhances precipitation signi cantly as the MYFC develops, and the e ect weakens rapidly when the MYFC decays during its eastward propagation. QN crst shows little impacts on rainfall during the onset and mature phases whereas it displays signi cant role during the decay phase. QN alst and QN curv, QN shdv and QN crst show cancellation only during the decay period.