Impact of Vertical Wind Shear on Summer Orographic Clouds over Tian Shan Mountains: A Case Study Based on Radar Observation and Numerical Simulation

Abstract

In this research, a summer orographic precipitation process that occurred over the Tian Shan Mountains on 27 July 2019, was investigated, focusing on the impact of vertical wind shear on clouds. Multiple remote sensors were deployed to measure the ambient conditions and the fine structures of clouds and precipitation, including a radiometer, a vertically pointing micro-rain radar (MRR), and a cloud radar on a truck. In addition, a convection-permitting simulation was conducted to investigate the role of vertical wind shear. The results show that (1) according to the MRR measurements, the precipitation was mainly due to a warm rain process and was mostly light to moderate, with no strong convection occurring; (2) the cloud structures observed by the cloud radar were very different above and below the shear level, and the cloud evolution was strongly controlled by the vertical wind shear, and (3) radar observations and model simulations indicated that vertical wind shear had an inhibiting impact on the vertical development of clouds and was responsible for the formation of multi-layer clouds. The analysis highlights the advantages of the use of millimeter radars to measure the fine structures of orographic clouds; thus, they can be powerful tools with which to improve our understanding of the interactions occurring between vertical wind shear and clouds over complex terrain.