WRF模式不同地形平滑方案对降水预报的影响

基于重庆市气象局中尺度数值预报业务系统,开展不同地形平滑方案对模式降水预报的影响研究,详细对比WRF模式中不使用地形平滑方案以及使用s-d-s和1-2-1两种平滑方案生成的静态地形高度场的差异,开展不同地形平滑方案批量平行试验并选取典型强降水个例进行对比分析,结果表明:不同地形平滑方案生成的静态地形高度场之间有明显的差异,特别是在地形较为陡峭的高原和山脉等地区,最大绝对偏差可达462.56m;s-d-s和1-2-1两种地形平滑方案主要平滑掉了模式地形中较小尺度的地形特征,且总体而言1-2-1方案的平滑效果比s-d-s方案明显。连续一个月批量平行试验降水预报检验结果表明,进行模式地形平滑对大雨及以上量级降水预报有正面影响,且使用1-2-1平滑方案的预报结果优于使用s-d-s平滑方案的预报结果;降水个例对比分析结果表明:采用不同的地形平滑方案会造成垂直速度和水汽通量散度预报的明显差异,这样的明显差异会进而影响强降水预报的落区和强度。

Influence of Different Terrain Smoothing Schemes in WRF Model on Precipitation Forecast

Based on the mesoscale numerical forecast system that is operationally implemented in the Chongqing Meteorological Service, the influence of different terrain smoothing schemes in the WRF model on precipitation forecast is studied. The differences between the static terrain height fields generated without smoothing and with two smoothing schemes (s d s and 1 2 1) in the WRF model are studied and compared in detail. Based on this, one month consistent experiments using different terrain smoothing schemes were carried out, and a typical heavy precipitation case was selected for further comparative analysis. The results show that there are obvious difference between the static terrain height fields generated by different terrain smoothing schemes, especially for the steep plateau regions or mountain regions while the maximum mean absolute error can be more than 462.56 m; the two terrain smoothing schemes (s d s and 1 2 1) mainly smooth out the topographic features of small scale in the mode terrain, and in general, the smoothing degree of the 1 2 1 scheme is greater than that of the s d s scheme. The verification results of the one month consistent experiments show that the model terrain smoothing process has a positive impact on the forecasts of heavy or above rainfall, and the prediction results using the 1 2 1 smoothing scheme are better than those using the s d s smoothing scheme. The comparative analysis results of a typical precipitation case show that different terrain smoothing schemes will cause significant differences in the prediction of vertical velocity and water vapor flux divergence, and such significant differences will further affect the fall area and intensity of heavy precipitation prediction.