Diagnostic Analysis of Wave Action Density During Heavy Rainfall Caused by Landfalling Typhoon

: Based on prior investigation, this work defined a new thermodynamic shear advection parameter, which combines the vertical component of convective vorticity vector, horizontal divergence, and vertical gradient of generalized potential temperature. The interaction between waves and fundamental states was computed for the heavy-rainfall event generated by landfalling typhoon “ Morakot ” . The analysis data was produced by ADAS [ARPS (Advanced Regional Prediction System) Data Analysis System] combined with the NCEP/NCAR final analysis data (1°×1°, 26 vertical pressure levels and 6-hour interval) with the routine observations of surface and sounding. Because it may describe the typical vertical structure of dynamical and thermodynamic fields, the result indicates that the parameter is intimately related to precipitation systems. The parameter ’ s positive high-value area closely matches the reported 6-hour accumulated surface rainfall. And the statistical analysis reveals a certain correspondence between the thermodynamic shear advection parameter and the observed 6-hour accumulated surface rainfall in the summer of 2009. This implies that the parameter can predict and indicate the rainfall area, as well as the initiation and evolution of precipitation systems.