The TianShan Rain-shadow Influence on the Arid Climate Formation in Northwestern China

The role of mountain ranges upon the arid climate formation in northwestern China is investigated using regional climate model. Two kinds of numerical experiments are carried out with real topography and with modified topography which does not contain the TianShan Mountains. Simulated rainfall distribution with real topography shows maximum precipitation in upwind slope of the mountain and minimum precipitation in downwind side of it, which coincides with the features of rain-shadow in other regions of the world. However, numerical experiment without the TianShan Mountains also simulates the area of distinct minimum precipitation in the same location. The arid climate, therefore, is formed even though the rain shadow effect is absent. The difference in rainfall amount between these two experiments is very small around downwind arid region. On the other hand, more intense and frequent rainfall events tend to occur in upwind of the mountain range due to forced lifting of environmental flow, which just emphasizes the precipitation contrast between upwind and downwind side of the mountain. The precipitation accompanied with the synoptic scale disturbances is suppressed over the arid region whether the TianShan Mountains exist or not.