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

<正>Following similar derivation of quasi-geostrophic Q vector（QG）,a new Q vector（QN） is constructed in this study.Their difference 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 5-6 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:QalstN（along-stream stretching）,QcurvN（curvature）, QshdvN（shear advection）,and QcrstN（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 2▽·QalstN is similar to that of 2▽·QN and mainly accounts for 2▽·QN during the entire period of Meiyu.The effects of QcurvN on rainfall enhancement fade from the mature stage to decay stage.QshdvN enhances precipitation significantly as the MYFC develops,and the effect weakens rapidly when the MYFC decays during its eastward propagation.QcrstN shows little impacts on rainfall during the onset and mature phases whereas it displays significant role during the decay phase.QalstN and QcurvN,QshdvN and QcrstN show cancellation only during the decay period.