河北冬季一次冷锋降雪云系微物理演变特征综合观测分析研究

A Comprehensive Observational Study of Micro-physical Evolution Characteristics of a Snowfall Cloud System under Winter Cold Front in Hebei Province

利用河北省中南部地区皇寺国家观测站布设的毫米波云雷达、微雨雷达结合飞机等联合观测数据,对2019年2月14日河北中南部地区一次冷锋降雪云系微物理演变特征进行分析,探讨雷达回波与冰雪晶粒子微结构的关系,以便更好地认识该地区自然降雪的宏微观结构特征。研究结果表明:降雪初生阶段表现为双层云结构,中云云顶高约4100 m,云底高约3600 m,低云云顶高约3100 m,云底高约200 m,中间存在一干层,3000 m以下高度粒子增长以凇附过程为主。降雪发展阶段上下两层云相接,雷达回波强度较强的时段地面降水量也较大,该时段降雪过程主要以凝华-聚并增长为主。降雪后期回波强度最大值减小,云顶高降低,3000 m以下高度范围内回波强度、多普勒速度、谱宽随高度降低呈增大趋势;飞机观测结果显示,降雪消散阶段逆温层底部由于水云云层较薄,催化潜力较小,冰雪晶粒子主要位于云的中上部,随着高度降低,冰雪晶粒子在下落过程中增大,与雷达观测结果一致,毫米波云雷达和微雨雷达反射率因子随高度变化与降水粒子有效粒径之间相关系数分别为0.89和0.83,雷达反射率因子主要受冰雪晶等大尺度粒子主导。

In order to better understand the macro and micro structure characteristics of snow clouds,the vertical structure and evolution of a frontal snowfall process on February 14,2019,are examined using the dataset of Micro Rain Radar(MRR)and Ka-band Cloud Radar(CR)combined with aircraft observation at Huangsi national meteorological station in the south-central part of Hebei Province.The results are as follows:During the initial stage of snowfall,there was a double-layer cloud structure with a dry layer in the middle.The cloud top and base height of the medium cloud were about 4100 m and 3600 m,respectively.The height of the low cloud top and bottom were 3100 m and 200 m,respectively.The growth of particles below 3000 m in the lower cloud was mainly due to the process of rime attachment.During the snowfall development stage,the upper and lower layers of cloud were connected,and the amount of snowfall on the ground was larger in the period with stronger radar echo intensity.The snowfall process in this period was mainly dominated by condensation and aggregation growth.During the late stage of snowfall,the maximum echo intensity and the cloud top height decreased.The echo intensity,doppler velocity and spectral width increased with the decreasing height below 3000 m.Aircraft observation results show that due to the thin water cloud,it was unsuitable for catalytic operation at the bottom of the inversion layer during the late snowfall period.Ice and snow particles were mainly located in the middle and upper part of the cloud and grew bigger during the falling process as the height decreased,which is consistent with radar observation.The correlation coefficient between millimetre wave cloud radar/MRR reflectance and the effective diameter of precipitation particles were 0.89 and 0.83,respectively.Radar reflectivity factors were mainly dominated by large-scale particles such as ice and snow crystal particles.