针对2008年7月20-22日四川盆地区域性暴雨过程, 通过引入高分辨率的地形数据构造不同的模式地形, 进行了WRF模式综合地形处理方法(TESTC)、不同多项式截断阶数的切比雪夫滤波方案(TEST5)和5点权重平均处理方案(TEST7)的地形试验。结果表明: (1)引入不同分辨率的地形数据, 且采用不同的地形滤波方法, 对模式预报效果是不一样的。相对而言, 基于高分辨率地形数据, 采用90截断阶数的TEST5试验略显优势。(2)三种地形处理方案不同程度地反映了主要降雨带的位置和强度, TEST5试验模拟的四川盆地东部降水强度较实况偏强, 但降水演变和降水落区更接近实况, TEST7试验总体模拟效果介于TESTC和TEST5之间。(3)不同地形处理方案带来四川盆地及周边地形高度和坡度的变化, 通过影响与中尺度系统相伴的物理量, 进而影响降水落区、强度与降水进程。(4)由于地形处理差异, 在四川盆地东部地形坡度较大区, 地形扰动增强风场脉动, TEST5试验带来更大的东西风切变, 而水平风场的辐合使低涡系统加强, 辐合上升运动加强, 将更多的低层水汽带到高空。TEST5试验模拟的低涡更强、位置偏东, 导致低涡影响下的降水强度更强, 落区偏东。

Based on high resolution terrain data, terrain experiments using different terrain disposal methods, including WRF synthetic terrain disposal method(TESTC), Chebyshev polynomial filtering method(a representative experiment TEST5) and five points weighed average method(TEST7) have been done for an heavy rainstorm occurred in Sichuan during 20-22 July 2008. The results show as follows: (1) Using terrain data at different resolutions and adopting different terrain filtering methods have different effects on the prediction results of numeric weather prediction model. Comparatively, based on high resolution terrain data, Chebyshev polynomial filtering method of using 90 truncation rank shows a slight predominance over other methods. (2) Three kinds of terrain disposal methods can predict main precipitation area and intensity. Although precipitation intensity simulated by TEST5 is stronger than the real, simulated precipitation evolution and precipitation area are closer to the real than that of TESTC and TEST7. As to overall simulation effect, TEST7 is between TESTC and TEST5. (3) Different terrain deposal schemes bring about changes to the model terrain altitude and slope of basin and surrounding area, and such changes impact on precipitation areas, intensities and evolutions by working on physical elements going with meso-scale systems activities. (4) Due to differences of terrain disposal, in the east basin where terrain gradient is bigger, topographic perturbation boosts up wind field fluctuation and TEST5 brings about bigger east-west wind-shear. The wind convergence strengthens low vortex and ascend motion, inducing more low-layer vapor being transported to upper air. The intensity of low vortex simulated by TEST5 is stronger and the low vortex position is more eastward, leading to stronger precipitation intensity and more eastward precipitation position than TESTC and TEST7.