The effect of two kinds of terrain-following coordinates on the simulation of a severe precipitation process

Selecting a classic height-based terrain-following coordinate (hereafter as Gal-C. S. coordinate) and a new smoothed level vertical height-based terrain-following coordinate (hereafter as SLEVE1 coordinate), the numerical simulations for a severe precipitation process and the comparative analysis on effects of two kinds of terrain-following coordinates on the simulating results were performed with the GRAPES_Meso regional model. Numerical simulations of the severe precipitation process show that the GRAPES_Meso model using SLEVE1 coordinate could improve the accuracy of the PGF (Pressure Gradient Force) calculations and the elements forecasts such as precipitation, wind, temperature and geopotential height. Comparing with Gal.C.S coordinate, SLEVE1 coordinate reduced the hypocritical precipitation caused by the hypocritical vertical velocity through smoothing the topographic factors in the coordinate planes. The small-scale noise in the isoclines was decayed to a certain degree in the vertical cross section of the elements of SLEVE1 coordinate, so the RMS errors were reduced and the correlation coefficients were increased. Besides, the smaller the critical decaying height of SLEVE1 coordinate was, the better the simulation results were. The critical decaying height of SLEVE1 coordinate is bound by the maximum terrain height.