Retrieval of Atmospheric Vertical Motion Velocity and Raindrop Spectrum for a Convective Cloud Precipitation
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摘要: 反演大气垂直速度和雨滴谱分布是研究云降水机制和云微物理信息的重要内容，对人工预报天气、干预天气都有重要意义。针对2021年8月29日安徽省内毫米波雷达探测到的一次对流云降水过程，处理毫米波雷达的功率谱数据并进行大气垂直速度和雨滴谱反演。在小粒子示踪法的基础上引入改进小粒子示踪法：选取有效云信号段中最小功率对应的谱点作为反演大气垂直速度的示踪物。首先，根据改进前后的小粒子示踪法分别从功率谱数据中反演大气垂直速度，并跟基数据反演大气速度的结果展开对比分析。进一步得到粒子在静止空气中的下落速度，根据现有粒子下落速度-粒子直径之间的经验公式计算反演粒子直径。研究表明：(1) 采用改进后的小粒子示踪法反演大气垂直速度得到的结果比小粒子示踪法得到的结果更精确，在云层内部两者误差较大；(2) 进一步得到粒子下落速度，结合探测时段的天气状况，得到的粒子速度与大气速度可很好地契合，跟对流云天气情况信息大致吻合；(3) 粒子浓度是反演雨滴谱分布时需要注意的主要参数，云在快速发展过程中，内部粒子持续朝外部扩张，云内部的粒子浓度较小，云边界的粒子浓度反而较大。Abstract: Retrieval of atmospheric vertical velocity and raindrop spectrum distribution is important in the study of cloud precipitation mechanism and cloud microphysics, which is of great significance for artificial weather prediction and weather intervention. For a convective cloud precipitation detected by a millimeterwave radar in Anhui province on August 29, 2021, this work processed its power spectrum data and retrieved atmospheric velocity and raindrop spectrum. The small particle tracer method is introduced and improved. The points which correspond to the minimum power in the effective cloud segment were selected as tracers for retrieving atmospheric vertical velocity. First, according to the small particle tracer method and the improved one, atmospheric velocity from the power spectrum data is obtained. Then, a comparative analysis is carried out against the results of the atmospheric velocity retrieved from the base data. The falling velocity of particles in still air is then obtained. According to existing empirical formula between particle falling velocity and particle diameter, particle diameters were calculated. The research is shown as follows. (1) The results of atmospheric velocity obtained by the improved small particle tracer method are more accurate than those obtained by the original method, and the error between the two methods is larger inside the cloud than outside of it. On this basis, the particle falling velocity is further obtained. Combined with the weather conditions during the detection period, the obtained particle velocity can well match with the atmospheric velocity and is consistent with the information of convective cloud weather. Particle concentration is the main parameter for retrieving the spectral distribution of raindrops. During the rapid development of the cloud, internal particles keep expanding to the outside, and particle concentration inside the cloud is small but relatively (and unexpectedly) large at the cloud boundary.
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表 1 毫米波雷达主要参数
参数名称 毫米波雷达 发射频率 33.4 GHz 天线类型 偏馈抛物面 垂直波束 0.4 ° 水平波束 0.4 ° 距离库长 30 m 探测距离 0~18 km 发射机类型 速调管 发射机峰值功率 9 kW 
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表 2 毫米波段下不同相态和温度条件下的|K|2
水粒子 冰粒子 温度/℃ |K|2 温度/℃ |K|2 0 0.870 0 0.200 100 0.900 -10 0.176 20 0.930 -20 0.176
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