两种地形追随坐标对一次强降水过程模拟影响对比分析

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

利用GRAPES_Meso区域中尺度模式,选择传统追随坐标(简称Gal.C.S坐标)和新的平缓追随坐标(简称SLEVE1坐标)两种高度地形追随坐标,对一次强降水天气过程进行数值模拟,对比分析两种不同地形追随坐标的影响。个例模拟结果表明,SLEVE1对降水场、风场、温度场、高度场的模拟预报均有改进;与Gal.C.S坐标相比,SLEVE1坐标通过平滑坐标面上的地形作用,减小虚假垂直速度进而减少虚假降水;SLEVE1坐标模拟的各要素场剖面图等值线上的小尺度噪音有不同程度衰减,预报要素均方根误差减小,相关系数增大;SLEVE1坐标临界衰减高度越小,模拟预报结果越好,该高度受到最大地形高度的约束。

Selecting a classic height-based terrain-following coordinate （hereafter as Gal-C. S. coordinate） and a new smoothed level verti- cal 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 SLEVE 1 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 SLEVE 1 coordinate was, the better the simulation results were. The critical decaying height of SLEVE1 coordinate is bound by the maximum terrain height.