切比雪夫多项式在模式地形平滑中的应用研究

Research on Application of Chebyshev Polynomial Filtering Method in Smooth Topography of GRAPES Model

利用切比雪夫多项式展开滤波方法获得较为平滑的模式地形,并对2008年7月20～22日四川省一次大暴雨过程进行了数值模拟,通过地形敏感性试验讨论了地形对暴雨的影响作用以及平滑地形对GRAPES模式的适用性。结果表明,切比雪夫多项式展开滤波方案选取高阶截断项数,促使模式地形更为平滑,地形高度变化使得垂直速度发生变化,进而引起降水变化,上升运动强度增强(或减弱)引起该区域内雨强增强(或减弱)。2008年7月2～28日连续26天的试验表明,切比雪夫多项式展开滤波方案对GRAPES模式中的小雨和中雨预报有改善作用,对大雨和暴雨改善较小。总体来看,切比雪夫多项式在地形平滑中对降水预报有正的效果。

Using the Chebyshev polynomial filtering method to obtain relatively smooth topography which was used in GRAPES model,a heavy rainstorm occurred in Sichuan Province during 20～22 July 2008 was simulated to discuss the impact of topography on precipitation according to topography sensitive test,as well as the applicability of smooth topography to the GRAPES model.The results show that Chebyshev polynomial filtering method through reducing the height of mountain and uplifting the height of depressions to achieve a smooth terrain,change of terrain height makes the vertical velocity change,thus causing changes in precipitation,increase in ascend exercise intensity is increased（or decreased） in the region caused by the rain intensity is enhanced（or weakened）.The results of 26-day experiment during 2～28 July 2008 show that,Chebyshev polynomial filtering method has improved effect on light rain and moderate rain of GRAPES model,has smaller improved effect on heavy rainstorm and rainstorm.In generally,the Chebyshev scheme has the effect to the precipitation forecast.