Diagnostic analysis of dynamical parameters for Hunan persistent heavy rain event in late June 2017

For a persistent heavy rain case occurred between 22 June and 2 July 2017 in Hunan, dynamical parameters, including the moist thermodynamic advection parameter, thermal helicity and the thermodynamic wave-activity density, were calculated. The vertical structure characteristics of physical parameters as well as dynamic and thermodynamic properties of precipitation background field were analyzed using data obtained from the NCEP/NCAR Global Forecasting System (GFS) model. Results showed that:(1) Sustained storm rainfall case was caused by the coupling of high level jet and low level jet, the maintaining of Baikal Lake blocking high and Western Pacific subtropical high, and rich water vapor transport. (2) All dynamical parameters showed strong signals in the persistent heavy rain area. In particular, the moisture divergence vertical flux and thermodynamic wave activity density were highly correlated with this sustained storm rainfall. (3) Moisture divergence vertical flux and thermodynamic wave activity density are of considerable importance in the diagnosis and prediction of storm rainfall in this region.