Numerical study on structure of meso-β scale rainstorm system during IOP523 of HUAMEX

One of the scientific goals of HUAMEX (Torrential Rainfall Experiment over Both Sides of the Taiwan Strait and Adjacent Area), a special project in th e National "863" Scientific Project, is to reveal meso- scale structure of heavy rainfall. However, limited by the observational instruments, the resolution of the data attained from the outfield scientific observation network cannot reveal the meso-scale structure. A 36-h numerical simulation of heavy rainfall case from May 23 to May 24, 1998 during IOP523 of HUAMEX was performed by the mesosc ale numerical model of PSU/NCAR MM5, and the meso- scale structure of convective system was examined based on the model output in this note. The results point out that the meso- scale features of the heavy rainfall are clear considerably at low, middle and upper levels, respectively. There is a strong ageostrophic feature between the geopotential height field and the wind field on the upper leve l. The vertical cross sections of 54 km coarse grid and 18 km fine grid both sho w the vertical circulation cells of the rainstorm clearly, which include a desce nding middle-level rear inflow and strong ascending low-level inflow. More impor tantly, the 18 km fine grid vertical section reveals another shallow vertical ci rculation cell in the planetary boundary layer (PBL) below 900 hPa, which relate s to the draggle flow resulting from the falling raindrops.