Microphysical Characteristics of A Cold Front Snowstorm Event in the West Tianshan Mountains
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摘要: 基于二维视频雨滴谱仪联合毫米波云雷达、风廓线雷达、微波辐射计、GPS/MET水汽等垂直探测设备，对2020年2月18～19日西天山地区一次冷锋暴雪过程进行了微物理特征研究。本文设计了雪花及霰粒子分类算法，用于定量研究降雪微物理特征。结果表明：（1）冷锋入侵、动力强迫阶段，降雪粒子类型主要为雪花，微物理过程主要为凝华增长及聚并增长；（2）冷锋控制、大风降温阶段，降雪粒子类型主要为雪花、霰粒子，微物理过程主要是聚并增长及凇附过程，同时聚并增长有利于凇附过程的发生；（3）在冷锋过境阶段，由于云顶温度升高、大气冰核减少、充足的过冷水，有利于凇附过程的发生。不同于南京地区的降雪，西天山地区降雪，雪花直径及雪强偏小，但霰粒子对雪强有较大贡献。通过两种融化模型，拟合出相应的雨滴谱及其Gamma分布，发现与本地层状云降水的特征相似。Abstract: Based on a two-dimensional video disdrometer, combined with cloud radar, wind profile radar, microwave radiometer, GPS/MET water vapor, and other vertically-scanning instruments, the microphysical characteristics of a cold front snowstorm event in the West Tianshan Mountain on February 18 and 19, 2020, were analyzed and studied. A classification algorithm for the snowflake and graupel was designed to quantitatively study the microphysical characteristics of the snowfall. The results show that (1) in the cold front invasion and dynamic forcing stage, the precipitation particles are mainly snowflakes and the microphysical processes are deposition and aggregation; (2) in the stage of cold front control bringing wind chill, the precipitation particles are snowflakes and graupel, and the microphysical processes are aggregation and riming, with the aggregation exhibiting a positive impact on the riming; (3) in the cold front passage, less ice nucleation and enough subcooled water favor riming due to the rise of the cloud top temperature. Unlike those in Nanjing, the snowflake diameter and snow intensity in the West Tianshan Mountains are relatively small, but graupel has a greater contribution to the snow intensity. The raindrop size and Gamma distributions are fitted using two melting models, similar to the characteristics of local stratiform cloud precipitation.
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Key words:
- West Tianshan region /
- Solid precipitation /
- Riming /
- Microphysical characteristics
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图 1 2020年2月17日09:00（协调世界时，下同）至19日08:00新源站气象要素地面观测数据
Figure 1. Ground data observed of meteorological elements at Xinyuan station from 0900 UTC February 17 to 0800 UTC February 19, 2020
图 2 2020年2月18日12:00 500 hPa位势高度场（等值线，单位：dagpm）、温度场（红色虚线，单位：°C）以及风场（黑色箭头，单位：m s−1）（红色方框为西天山地区）
Figure 2. Geopotential height (contours, units: dagpm), Temperature (red dotted line, units: °C), Wind (black arrow, units: m s−1) at 1200 UTC February 18, 2020. The red box represents the western Tianshan Mountain area
图 3 2020年2月17日09:00至19日08:00新源站CFL-03型边界层风廓线雷达观测数据。彩色阴影风向杆表示风场，单位：m s−1
Figure 3. Observation data of CFL-03 boundary wind profiler radar of Xinyuan Station from 0900 UTC on February 17 to 0800 UTC on February 19, 2020. Color shadow barbs represent wind fields, units: m s−1
图 4 2020年2月18日00:00至19日05:00新源站MP-3000型微波辐射计观测数据：（a）温度（单位：K）；（b）水汽含量（单位：g m−3）；（c）液水含量（单位：g m−3）；（d）相对湿度
Figure 4. (a) Temperature (units: K), (b) water vapour content (WVC, units: g m−3), (c) liquid water content (LWC, units: g m−3), and (d) relative humidity data observed using the MP-3000 microwave radiometer at Xinyuan station from 0000 UTC February 18 to 0500 UTC February 19, 2020
图 5 二维视频雨滴谱仪2DVD探测粒子的分类：（a）雪花；（b）霰粒子。图中黑色虚线为雪花的V–Deq（粒子速度—粒子等效体积直径）关系，红色虚线为雨的V–Deq关系
Figure 5. 2DVD (Two Dimensional Video Disdrometer) particle classification: (a) Snowflake; (b) graupel. The black dotted line corresponds to the V–Deq (particle velocity–particle equivalent volume diameter) relationship of snowflakes, and the red dotted line denotes the V–Deq relationship of rain
图 6 2020年2月18日00:00至19日07:00新源站KPS-HMB型单通道毫米波云雷达观测数据：（a）反射率因子（填色；单位：dBZ），虚线为温度廓线（单位：°C）；（b）径向速度（填色；单位：m s−1），红色虚线液水含量（单位：g m−3）
Figure 6. Observation data of the Xinyuan station’ s KPS-HMB single-channel millimeter-wave cloud radar from 0000 UTC February 18 to 0700 UTC February 19, 2020: (a) Reflectivity factor (shaded, units: dBZ), the gray dotted line denotes the temperature profile (units: °C); (b) radial velocity (shaded, units: m s−1); the red dotted line denotes the liquid water content (units: g m−3)
图 7 2020年2月18日10:20至19日03:55新源站2DVD观测数据：（a）粒子中值体积直径（D0），粒子最大直径（Dmax）；（b）粒子数浓度（Nt）；（c）雪花和霰粒子的雪强（SR）
Figure 7. Observation data from Xinyuan station 2DVD from 1020 UTC February 18 to 0355 UTC February 19, 2020: (a) Median volume diameter (D0) particles and the maximum diameter (Dmax) particles; (b) particle number concentration (Nt); (c) snow rate (SR) of snowflake and graupel
图 8 2020年2月18日10:20至19日03:55新源站2DVD观测数据：（a）粒子大小分布（PSD）；（b）粒子速度分布（PVD）。彩色阴影表示数量（单位：个）
Figure 8. Observation data from Xinyuan station 2DVD from 1020 UTC February 18 to 0355 UTC February 19, 2020: (a) PSD (particle size distribution); (b) PVD (particle velocity distribution). Color shadows represent quantity (units: count)
图 9 2020年2月18日（a）10:20～16:00、（b）16:05～23:55、（c）19日00:00～03:55粒子大小分布及Gamma分布。红实线是雪粒子Gamma分布；黑色实线是MC模型Gamma分布；蓝色实线是FC模型雨粒子Gamma分布；红色点是雪粒子分布；黑色点是MC模型雨滴分布；蓝色点是FC模型雨滴分布
Figure 9. Particle size and gamma distributions during (a) 1020 UTC–1600 UTC, (b) 1605 UTC–2355 UTC 18 February, and (c) 0000 UTC–0355 UTC 19 February 2020. The solid red line is the gamma distribution of snow particles. The solid black line is the MC model gamma distribution. The solid blue line is the rain particle gamma distribution of the FC model. The red dots are snow particles; the black dots are the MC model raindrop distribution; and the blue dots represent the FC model raindrop distribution
图 10 2020年2月18日10:20至19日03:55降雪过程流程图
Figure 10. Flowchart of snowfall from 1020 UTC February 18 to 0355 UTC February 19, 2020
表 1 毫米波云雷达主要参数
Table 1. Key parameters of cloud radar
工作频率 极化方式 天线增益 波束宽度 探测范围 时间分辨率 35.5 GHz 单发单收线极化 ≥52 dB ≤0.4° 120 m～20 km 1 min 
下载: 导出CSV
表 2 风廓线雷达主要参数
Table 2. Key parameters of wind profile radar
工作频率 最小探测高度 最大探测高度 时间分辨率 高度分辨率 波束宽度 1320 MHz 60 m ≥3 km 五波束≤6min ≤60 m（低模式）
≤120 m（高模式）≤6°
下载: 导出CSV
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