Study on Radar Detection of One Stratiform Cloud Precipitation Process in the Central Part of the Tianshan Mountains in China

Abstract

In order to investigate the physical structure characteristics of the clouds and precipitation over the Tianshan Mountains in summer, the Urumqi Institute of Desert Meteorology of China Meteorological Administration (CMA) carried out an atmospheric detection experiment in Bayanbulak from 1st to 31st August 2012 by means of a wind-profiling radar and a Doppler weather radar. Using the radar observation data, this paper analyzes the dynamic, thermodynamic, radar echo intensity and macro-micro structure characteristics of the 2–3 August precipitation process. The results show that: (1) The radar echo intensity of this rainfall process changes within 5–38 dBZ, and the precipitation cloud system is under the height of 6500 m, with notable 0 °C level echo bright band between 1200 m and 2000 m height. NCEP analysis data shows that the cloud top temperature ranges from −25 °C to −32 °C. These indicate the features of typical stratiform cold cloud precipitation. (2) Atmospheric motion during the precipitation process presents the multi-layer structure with wind velocity varying within the range of 3.0–8.0 m/s. The temperature advection is presented with the vertical structure distribution of “cold-warm-cold”, which indicates relative stability of the atmospheric stratification. (3) By retrieving and analyzing the raindrop size distributions below 0 °C level bright band within 600–1200 m height, when the precipitation evolve from early stage to its peak stage, the concentration of the tiny particle zone (D ≤ 2.5 mm) changes a little while the concentration of the medium particle zone (2.5 4 mm) increase considerably; but after peak stage the concentration in the medium particle zone and the concentration in the large particle zone decline first, then the concentration in the tiny particle zone reduces. (4) Raindrop size distribution data is used to calculate the precipitation intensity and the liquid water content, whose spatial-temporal variation characteristics are the same. During peak stage of the precipitation, the instantaneous precipitation intensity reaches 5.0 mm/h, and the liquid water content reaches 0.35 g/m3. This study would help deepen the understanding on the physical structure of the clouds and precipitation over the Tianshan Mountains in summer, and also provide some scientific basis for cloud seeding operation over this area.