Observational Study on the Supercooled Fog Droplet Spectrum Distribution and Icing Accumulation Mechanism in Lushan, Southeast China

Abstract

A fog monitor, hotplate total precipitation sensor, weather identifier and visibility sensor, ultrasonic wind speed meter, an icing gradient observation frame, and an automated weather station were involved in the observations at the Lushan Meteorological Bureau of Jiangxi Province, China. In this study, for the icing process under a cold surge from 20–25 January 2016, the duration, frequency, and spectrum distribution of agglomerate fog were analyzed. The effects of rain, snow, and supercooled fog on icing growth were studied and the icing and meteorological conditions at two heights (10 m and 1.5 m) were compared. There were 218 agglomerate fogs in this icing process, of which agglomerate fogs with durations less than and greater than 10 min accounted for 91.3% and 8.7%, respectively. The average time interval was 10.3 min. The fog droplet number concentration for sizes 2–15 μm and 30–50 μm increased during rainfall, and that for 2–27 μm decreased during snowfall. Icing grew rapidly (1.3 mm h⁻¹) in the freezing rain phase but slowly (0.1 mm h⁻¹) during the dry snow phase. Intensive supercooled fog, lower temperatures and increased wind speed all favored icing growth during dry snow (0.5 mm h⁻¹). There were significant differences in the thickness, duration, density, and growth mechanism of icing at the heights of 10 m and 1.5 m. Differences in temperature and wind speed between the two heights were the main reasons for the differences in icing conditions, which indicated that icing was strongly affected by height.

摘要

在江西省庐山气象局观测场布设了雾滴谱仪, 热盘雨量计, 现在天气现象仪, 超声风速仪, 积冰梯度观测架及自动气象站. 2016年1月20至25日寒潮过程中, 分析了团雾持续时间, 频率及谱分布, 探究了雨, 雪, 过冷雾对积冰增长的影响, 对比了两高度(10m, 1.5m)积冰增长和气象条件. 过程中共218个雾团, 持续时间小于10min和大于10min的雾团分别占91.3%和8.7%. 平均时间间隔为10.3min. 降雨时雾滴谱在2-15μm和30-50μm数浓度增加, 降雪时雾滴谱在2-27μm数浓度减少. 冻雨阶段积冰增长迅速(1.3 mm h^-1), 干雪阶段积冰增长缓慢(0.1 mm h^-1). 过冷雾的密集出现, 较低的温度及风速增加提高了干雪过程中的积冰增长率(0.5 mm h^-1). 10m和1.5m两高度积冰厚度, 时长, 密度及增长机制有显著差异. 温度和风速的差异是两高度积冰差异的主要原因, 说明积冰状况与积冰高度关系密切.