庐山一次积冰天气过程冻雨滴谱及下落末速度物理特征个例研究

利用PARSIVEL激光雨滴谱仪和自动气象站观测资料及MICAPS数据，对2014年2月7~15日庐山地区积冰天气期间持续时间在5 h以上的2次冻雨过程2月10日（个例1）和2月13日（个例2）]降水谱分布特征及下落末速度粒径分布进行研究。所观测到的两次个例均是以冻雨为主体的混合相态降水，下落末速度粒径分布偏离G-K曲线，与常规液态降水存在差异，低落速的冻雨滴随降水过程会逐渐向冰粒和干雪转化。结果表明:（1）个例1总降水粒子谱谱宽大于个例2，但峰值数密度比个例2小:个例1谱宽为10 mm，个例2谱宽为4.25 mm，两者峰值粒径均为0.5 mm；个例1降水粒子谱宽为干雪>冻雨>冰粒，个例2降水粒子谱宽为冻雨>干雪>冰粒。（2）Gamma分布更适合描述混合相态降水粒子谱以及冻雨滴谱，个例1中总降水粒子谱Gamma分布为:N（D）=20D-3.61exp（-0.08D），冻雨Gamma分布:N（D）=76D-2.18exp（-1.11D）；个例2中总降水粒子谱Gamma分布为:N（D）=30D-4.68exp（-0.75D），冻雨Gamma分布:N（D）=30D-4.67exp（-0.75D）。（3）混合相态降水因混有干雪或冰粒而使得下落末速度粒径谱分布表现出不同程度地向大粒径小落速方向或小粒径大落速方向延展的趋势，这为今后依据下落末速度粒径谱区分同时期降水类型提供了新的思路。

Physical Characteristics of Freezing Raindrop Size Distribution and Terminal Velocity in Two Ice Weather Cases in Lushan Area

Physical characteristics of winter precipitation in two ice weather cases that lasted for more than five hours during 7 Feb to 15 Feb 2014 are observed using PARSIVEL disdrometer, Automatic Weather Station (AWS), Meteorological Information Comprehensive Analysis And Process System (MICAPS) and other instruments. In this paper, spectral feature of precipitation and particle size distribution for the two cases (occurred on Feb 10 and Feb 13) are analyzed. Both cases were mixed-phase precipitation with freezing rain as the main body. The distribution of terminal velocity and particle size deviated from the G-K curve in the two cases. The mixed phase precipitation is different to conventional liquid-phase precipitation, and frozen rain drops gradually convert to ice and dry snow particles during the precipitation process. The results are as follows. (1) The spectral width of size distribution for total precipitation particles in Case 1 was greater than that in Case 2, whereas the peak number density in Case 2 was greater than that in Case 1. In Case 1, the spectral width of particle size distribution was 10 mm and the peak diameter was 0.5 mm; in Case 2, the spectral width of particle size distribution was 4.25 mm and the peak diameter was 0.5 mm; the spectral widths of size distribution of different precipitation particles are sorted from large to small as dry snow > freezing raindrops > ice pellets in Case 1 and freezing raindrops > dry snow > ice pellets in Case 2. (2) The Gamma distribution is more appropriate for describing and parametrizing the size distribution of freezing rain and mixed-phase precipitation. The Gamma distribution of total precipitation particles can be expressed by N(D)=20D^-3.61exp(-0.08D) in Case 1 and N(D)=30D^-4.68exp(-0.75D) in Case 2. The Gamma distributions for frozen raindrops are N(D)=76D^-2.18exp(-1.11D) and N(D)=30D^-4.67exp(-0.75D) for Case 1 and Case 2, respectively. (3) Mixed-phase precipitation includes dry snow and ice particles, and thus demonstrates an obvious tendency to different and non-empirical direction. This feature provides a new idea for distinguishing rainfall types in synchronous precipitation in the future.