地形对降水影响的数值试验

用MM5v3模式研究地形高度对江淮流域降水的影响,通过在模式中提高和降低大别山和黄山的地形高度来模拟降水的变化,个例是1998年6月28日和1991年6月12日的暴雨过程,进行了24 h模拟,并分析了垂直速度、涡散度、湿位涡、水汽通量等的变化,结果表明,上述各因子都在地形高度变化后有了明显变化,并因此影响了降水变化。各因子都有影响,综合各因子的影响是预测地形降水的途径之一。总的说,地形引起的降水变化主要在地形变化的附近,特别是在山的迎风面,降水有明显增加。决定降水落区和强度的主要仍是大中尺度环流,但地形起了改变落区和强度的作用。

A NUMERICAL EXPERIMENT ON THE EFFECT OF TERRAIN ON THE PRECIPITATION

The effect of terrain level on the precipitation in the Yangtze-Huaihe area is investigated by use of MM5v3 model,the change of precipitation is studied from raising and decreasing the terrain level in the model.The cases are the heavy rains on June 28,1998 and June 12,1991,24 hours simulations are performed,and the variations of vertical velocity,vorticity,divergence,moist potential vorticity and moist flux etc are also analyzed.The results show that all these factors are changed when the terrain level is changed,and then the variation of the precipitation can be influenced.Since all the factors can influence the precipitation,in order to predict the effect of the terrain on precipitation,all the factors must be considered.On the whole,the change of precipitation caused by terrain only occurs near the area of terrain change,the precipitation increases obviously in the upwind direction of the mountain.The main factor controlling the place and strength of the precipitation is the macro-and meso-scale circulation,the terrain can change the place and strength of precipitation.