基于飞机观测的华北积层混合云降水微物理特征的数值模拟研究

基于2009年5月1日积层混合云降水2架飞机观测数据分析，使用中尺度模式WRFV3对此次过程积云区和层云区的微物理特征和转化过程进行数值模拟比较研究。飞机观测数据分析表明，此次积层混合云中的层云区和积云区冰粒子形状和形成过程有明显差别，层云区的粒子形状组成比较复杂，包含针状、柱状和辐枝状等，而积云区主要以辐枝状粒子为主，聚并、凇附过程明显。数值模式能较好地模拟出此次积层混合云降水过程的基本特征，包括回波分布、飞行路径上降水粒子的数浓度和液态水含量等。数值模拟结果表明，云水相对丰富、上升气流强的层云区凇附过程较强，产生的雪在低层融化为雨水，为后期高层形成的雪和霰提供丰富的液态水，能发展成对流较强的积云区，存在播种—供给机制。在积云区，水成物的比例从大到小依次为雪（51.9%）、霰（31.0%）和雨水（16.0%）；雪的主要源项包括淞附增长（56.8%）和凝华增长（40.1%），霰的主要源项包括凇附增长（46.6%）、雨水碰并雪成霰（42.6%）和凝华增长（16.1%），雨水的主要源项是霰（77.6%）和雪（22.4%）的融化。而相对云水较少、上升气流较弱的层云区将保持层云的状态，层云区水成物的比例从大到小依次为雪（90.4%）、雨水（6.1%）、冰晶（3.5%）；高层冰晶和雪通过凝华过程增长，雪在零度层下融化为弱的降水。

Numerical Simulation Study on the Microphysical Characteristics of Stratiform Clouds with Embedded Convections in Northern China based on Aircraft Measurements

To characterize the microphysical characteristics and transformation process of stratiform clouds with embedded convections, a study was performed using the WRFV3 model and based on two aircraft measurements taken on May 1, 2009. The aircraft observation results showed that significant differences in the shapes and formation process of ice particles existed between the regions of stratiform cloud and embedded convection. Compared with the embedded convection region, the stratiform cloud featured more complicated shapes of ice crystals, including needle column, capped column, and dendrite types. However, the dendrite-type ice crystals dominated in the embedded convection region, and their growth was controlled by aggregation and riming processes. Overall, the results indicated that the basic characteristics of this stratiform cloud with embedded convections simulated by the WRF model agreed well with the aircraft observations, including cloud distribution, LWC, and numerical concentration on the flight route. The simulation results showed that in the stratiform cloud, with higher cloud water content and larger W, embedded convection could be developed because of a strong riming process. The hydrometeors of snow, graupel, and rainwater in the clouds accounted for 51.9%, 31.0%, and 16.0%, respectively, while cloud ice and cloud water accounted for very little. In the higher level, snow and graupel grew through deposition process. In the lower level, they grew through the riming process and melted into rain. Stratiform clouds with lower cloud water content and smaller W would remain as stratiform cloud. The hydrometeors of snow, rainwater, and cloud ice accounted for 90.4%, 6.1%, and 3.5%, respectively. The ice and snow grew through deposition process and melted into rain in the lower level.