雨滴谱垂直演变特征的微雨雷达观测研究

雨滴谱的垂直变化特征对于认识降水过程、改进模式和雷达定量估计降水等具有重要意义。利用2016年6月1日-9月30日雨量筒、微雨雷达（micro rain radar，简称MRR）和PARSIVEL雨滴谱仪连续4个月的观测数据，在对比3种仪器观测结果的基础上，研究了层状云降水不同降水强度下微物理特征量和雨滴谱垂直演变特征。结果表明:MRR与PARSIVEL雨滴谱仪观测降水强度相关性较好，且两种仪器观测的雨滴谱在中等粒子段（0.5~2.5 mm）表现出较好的一致性，而对于小粒子段（雨滴直径小于0.5 mm）PARSIVEL雨滴谱仪观测的数浓度明显低于MRR。对于弱降水（降水强度R ≤ 0.2 mm·h-1），液水含量和降水强度随高度降低减小，雨滴在下落过程中蒸发明显。对于较强降水（R>2 mm·h-1），随高度降低，雷达反射率因子增大，小滴数浓度减小的同时大滴数浓度增加明显，雨滴下落过程碰并作用明显。所有高度直径不超过0.5 mm的小滴对数浓度贡献均为最大。高层雨滴直径不小于1 mm的小粒子对降水强度的贡献可达50%，小粒子对降水强度贡献随高度降低减小。

Vertical Profiles of Raindrop Size Distribution Observed by Micro Rain Radar

Raindrop size distribution (DSD) is of great importance for understanding the microphysical process of precipitation, as well as improving the microphysical parameterization scheme in numerical model. Most studies of DSD focus on precipitation characteristics on the surface. However, vertical profiles of DSD and rain parameters are important for quantitatively accurate precipitation estimation from weather radars. Based on data observed by the ground-based PARSIVEL disdrometer and a vertical pointing micro rain radar (MRR) at Xingtai, Hebei Province located in North China from June to September in 2016, the vertical evolution of precipitation microphysical parameters and DSD of different rain rate classed for stratiform precipitation are analyzed. Measurements from MRR, rain gauge and ground PARSIVEL disdrometer are compared. Results show that measurements from MRR, rain gauge and PARSIVEL disdrometer have good agreement in rain rate. MRR and PARSIVEL disdrometer show good consistency in medium sized (1-2.5 mm) range of DSD but have slight differences for small and large raindrops. MRR observes much more small particles than PARSIVEL disdrometer. When the rain rate is low, with low relative humidity around the ground, both large and small drops decrease with the altitude decreasing, so as to the liquid water content and rain rate, which is explained by the evaporation. When the rain rate is high, the concentration of particles for precipitation is much larger, and the vertical variation of DSD is more obvious. The profiles of radar reflectivity show a positive slope(dZ/dH>0). The concentration of medium-sized and large raindrops increases obviously with decreasing altitude at the cost of reducing small raindrops for precipitation with rain rate between 2-20 mm·h^-1, indicating that the coalescence is the dominant process for 2-20 mm·h^-1. The largest contribution to the total number concentration is small drops (0-0.5 mm) with diameters between 0-1 mm and can reach up to 50% above altitude of 2 km. Small particles contribute less to the precipitation intensity as the altitude decreasing. These small raindrops account only 15% to the surface precipitation, while the medium-sized raindrops can contribute 60% with rain rate between 2-20 mm·h^-1. Large raindrops (>2 mm) is about 50% of the surface rainfall for the largest rain rate class. These results provide useful information for better understanding rain processes and quantitative estimation of precipitation in the future.