Aircraft Measurement of Microphysical Characteristics of a Topographic Cloud Precipitation in Qilian Mountains

Abstract

Qilian Mountains are an important ecological barrier in Northwest China. The precipitation in Qilian Mountains is mainly caused by topographical cloud system. Aircraft detection in Qilian Mountains is of great significance for deepening the understanding of cloud microphysical processes, and for scientifically and effectively carrying out artificial precipitation operations to improve the ecological environment. Using the airborne observations of a topographic cloud precipitation process in Qilian Mountains on 29 August 2020, the microphysical characteristics of the summer cloud precipitation process in Qilian Mountains are studied. The cloud system presents an obvious layered structure. The height of the cloud base is 4000 m, and the water content of the whole layer is relatively rich. The liquid water content (L) is between 0.65 and 1.1 g·m-3, and the cloud water large value area appears at 4500-5300 m altitude, which has a high concentration of cloud droplets. The water content of cloud water is mainly contributed by cloud droplets between 15 and 20 μm. The average concentrations of small cloud particles and large cloud particles are 7.54 cm-3 and 0.86 cm-3. The average effective diameters of small cloud particles and large cloud particles are 11.02 μm and 198.11 μm. The cloud particles in Qilian Mountains have the characteristics of small concentration and large diameter. There are obvious differences in cloud microphysical characteristics between the north and south slopes of Qilian Mountains. Affected by the topography, the concentration and diameter of cloud droplets on the northern slope are larger than those on the southern slope, and L on the northern slope are significantly larger than those on the southern slope too. The spectra of cloud droplets at different heights in Qilian Mountains are respectively unimodal distribution. The spectrum of cloud droplets with a diameter less than 50 μm can be fitted by Gamma distribution, while the spectrum of cloud droplets with a diameter greater than 50 μm shows a power exponent distribution. The ice crystals in the ice layer are mainly grown through the process of sublimation and coalescence. The growth mechanism of the ice crystals in the mixed layer is mainly the Bergeron process, and accompanied by attachment and aggregation growth.

Keywords

• cloud microphysical characteristics
• liquid water content
• cloud particle spectrum
• aircraft measurement