1.Key Laboratory for Aerosol–Cloud Precipitation of China Meteorological Administration,Nanjing University of Information Science Technology /Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters;2.Weather Modification Office of Xinjiang Uygur Autonomous Region,Xinjiang
Measurements were conducted using a micro-rain radar, a Ka-band cloud radar and a microwave radiometer to analyze the fine vertical structure and evolution process in an orographic precipitation process in the middle Tianshan area. In addition, a high-resolution simulation is made to analyze the instability and its influence on the generation of the clouds. The observations show that the precipitation was generated due to the convergence between the southwesterly wind flew across the mountain ridge and the northernly wind that induced due to the thermal forcing by terrain. Because the observed convective updraft was not strong enough, the low-level northernly flow turned to the south as it approaching the high-level southwesterly wind, forming strong wind shear. After the precipitation occurred, the low-level convective clouds were confined below the windshear layer, and the cloud tops were generally flat and low, indicating the windshear layer has a significant inhibiting effect on the convection. The model simulation suggests the influence of the wind shear on the development of precipitation clouds and the change of thermal instability on the northern slope of the Central Tianshan Mountains during this precipitation is very important. The advective transport of considerable potential temperature by upper-level southerly winds made the upper layer above the wind shear layer more thermally unstable, and made the layer below it more thermally stable, thus suppressing low-level convection and promoting upper-level convection. If low-level convective updrafts were not strong enough to break through the stable laminar junction caused by vertical wind shear, convection will be confined below the vertical wind shear layer, preventing intense precipitation.