上海地区几类强降水雨滴谱特征分析

用Parsivel激光降水粒子谱仪资料对2013年上海地区4—10月份期间4种类型 (层状云、对流暖云主导型、对流冷云主导型和强台风影响下的混合暖云型) 降水过程的雨滴谱特征进行了分析。通过平均雨滴谱及其拟合特征、雨滴数密度与含水量分布、雨滴尺度与速度二维谱分布等对比分析发现:各类降水中, 雨滴谱的峰值结构与雨强大小有关, 其中直径介于0.187~1.312 mm的小雨滴均出现峰值且总数最多。各尺度雨滴数密度及其比例决定了其降水量贡献比, 在冷云强降水中的雨强贡献最大的雨滴尺度要显著大于其他3种类型。雨滴谱宽按大小排列依次为对流冷云主导型、混合暖云型、对流暖云主导型和层状云。最后综合运用雨滴谱、雷达、雨量站、闪电等观测资料对9月13日对流冷云主导型降水过程进行分析后发现:在雷暴的演变过程中, 雨滴谱特征与雷达反射率因子、垂直液态水含量、自动站雨强、闪电频次等要素均有较好的相关性。冷云产生的冰晶和冰雹融化后的大雨滴进入中低层的广谱小雨滴群, 并通过破碎分裂增加了大雨滴的形成概率, 尤其是捕捉碰并过程更加快了大雨滴的增长速度, 使雨强在短时间内迅速加强。雨滴谱中各档粒子数的演变, 揭示了降水强度的变化, 用雨滴谱资料可有效弥补现有雷达定量估测降水的偏差, 且在冷云中改善明显。

Analysis on raindrop spectrum in four types of precipitation in Shanghai

By using data from Parsivel laser precipitation particle spectrometer, the raindrop spectrum characteristics of four types of rainfall: stratiform, warm convective clouds, cold convective clouds and warm mixed clouds triggered by a tropical cyclone in Shanghai from April to October 2013 are analyzed. Comparison among average raindrop spectrum and its fitting characteristics, distribution of raindrop density and water content, the distributions of raindrop size and two-dimensional spectrum velocity shows: (1) the peak structures of raindrop spectrum are related with the rainfall intensity in these cases, especially the little raindrops in the range of 0.187-1.312 mm diameters; (2)the density and its percentage of different sizes of raindrop determined its precipitation contribution proportion, and the size of raindrop with the highest rainfall contribution proportion in cold cloud precipitation is much larger than that in other three types; (3) the descending order of width of raindrop size spectra was cold convection cloud, warm mixed cloud, warm convection cloud and stratiform cloud. The comprehensive analysis on rainfall characterized by cold convective cloud on September 13 with rainfall spectrum data, radar data, rain gauge data and flash data found that in the evolution of this strong thunderstorm precipitation, a consistency existed between raindrop size distribution and other characteristics like radar reflectivity, vertically integrated liquid (VIL) above different levels, rain-gauge rain rate, and cloud-ground lightning flash rate. The ice crystals and hails produced in cold clouds melt into large drops, and then fell among small droplets and carried out coalescence and breaking made the rain rate grow rapidly. The maximum of different sizes of drops reflected the evolution of rainfall process. The comparisons between rain drop and radar products also suggested that a potential application of raindrop spectrum observations is able to compensate for the radar quantitative precipitation estimation, especially for cold cloud precipitation cases.