Airborne Observations of the Cloud Vertical Microphysical Characteristics of Warm Conveyor Belt within a Winter Mesoscale Snowstorm

The microphysical characteristics of the warm conveyor belt (WCB) within a winter mesoscale snowstorm in southern Hebei Province were analyzed using aircraft observation data. Influenced by the WCB associated with the Southwest vortex warm front, the cloud can be divided into three layers during the early period of snowfall. A few small-sized ice crystals existed in the upper part of the cloud. The thickness of the middle layer was equivalent to the thickness of the WCB (0.9 km). In this layer, the maximum liquid water content was 0.51 g m^–3, with a low concentration of ice crystals, and the vertical profiles of the liquid water content and the adiabatic water content were similar. In the lower part of the cloud, the number concentration of ice crystals increased by two orders of magnitude compared with the upper part of the cloud, and the particle spectrum width increased significantly. The predominant ice crystal habits were columns, bundles of columns, and graupel. Graupel particles were formed through the process of riming, which occurred in the middle layer with abundant supercooled water, and numerous columnar ice crystals were produced by the Hallett–Mossop mechanism. The abundance of supercooled water in the WCB considerably influenced the microphysical processes during the early snowfall period. The vertical structure of the cloud was relatively uniform during the later period of snowfall, as the jet at 700 hPa had moved out of the observation area. At this time, the predominant ice crystal habits were plates, and the particle size increased as the height decreased, reflecting the growth of the ice crystals through the aggregation process.