Vertical Observation and Numerical Simulation of the Clouds Physical Characteristics of Snow-Producing over Yanqing Mountain Area in Beijing

Snowfall was observed and analyzed by wind profiler radar, cloud radar, disdrometer, microwave radiometer, and automated meteorological readings on 23-24 March 2017 over Yanqing Mountain area in Beijing, combined with the mesoscale numerical model WRF. Results indicated that the vertically-scanning instruments in combination with the mesoscale numerical model obtained a snow macrostructure and microphysical information that can be applied to further snow studies. The snow process was triggered by the intersection of low-level southwesterly warm and moist flow and cold air formed by strong dynamics and moisture convergence, and attendant wind shear at 4-5-km height was conducive to the development and strengthening of the weather system. Updrafts aided in water vapor transmission, as well as ice-snow autoconversion, and deposition and aggregation between snow crystals, while a centered concentration of ice crystals corresponded with the upper boundary of the upward motion. However, in this case, supercooled cloud water at lower layers was insufficient, with an echo of < 20 dBZ, echo top < 7 km, snow vertical velocity < 2 m s^-1, and the moment of maximum snowfall corresponding to the lower strong echo area. Snow particle spectrum was narrow, with the majority comprising small particles about 1 mm in diameter. The main phase was dry snow, with a negligible area of mixed precipitation.