北京地区两次雨雪转换过程的相态模拟研究

Simulation Study on Phase State of Two Rain and Snow Processes in Beijing Area

利用中尺度数值模式WRF(Weather Research and Forecasting),对2015年11月2022日和2016年11月2021日北京地区两次雨雪转换过程进行数值模拟,根据模拟结果,结合探空等实况观测资料,分别对降水相态转换的机制进行了探讨,并比较分析了两次过程云微物理特征的差异。研究表明:中尺度数值模式WRF较为准确地模拟出了两次雨雪过程的降水量级和落区;同样是雨转雨夹雪过程,但是两次过程云中雪晶粒子的含量和分布的层次是截然不同的,导致相态转换的微物理过程也不同。2015年的过程,雪晶通过与过冷云(雨)滴的粘连碰冻作用而不断增长导致观象台的相态由雨转为雨夹雪;而2016年的过程,雪晶主要依靠冰晶的凝华、撞冻及碰并等机制而不断增长导致观象台的相态由雨转为雨夹雪。在预报冬季降水相态时,不仅要关注各标准层的经验阈值温度,还要充分关注模式产品中与微物理有关的水成物分布的层次和浓度大小。

Two rain and snow processes in winter during 2022 November 2015 and 2021 November 2016 were simulated by WRF meso-scale numerical model.Based on the simulation results and observational data,not only the mechanism of phase transformation was analyzed respectively,but also cloud microphysical features in two processes were compared.The results show that the precipitation grade and spatial distribution in two processes can be simulated well by WRF model.Although transformation from rain to sleet is occurred in both two processes,the content and distribution of snow crystal is completely different,which leads to the difference of cloud microphysical processes.As to the rain and snow process in 2015,the adhesion and collection of snow crystal to super-cooled cloud droplets and raindrops maybe cause the transformation from rain to sleet in Beijing observatory,while the deposition,accretion and collection growth of ice is the main microphysical processes in 2016.When forecast the phase state of precipitation in winter,not only the empirical threshold temperature of each standard layer should be paid attention to,but also the level and concentration of water substance related to microphysics in model products.