华北太行山东麓一次稳定性积层混合云飞机观测研究：对流云/对流泡和融化层结构特征

Aircraft Measurements of a Stable Stratiform Cloud with Embedded Convection in Eastern Taihang Mountain of North China: Characteristics of Embedded Convection and Melting Layer Structure

对云中微物理过程的研究是研究云降水形成过程和人工影响降水的重要基础,目前对积层混合云的对流区/对流泡中的微物理结构了解甚少。本文利用河北省"十三五"气象重点工程--云水资源开发利用工程的示范项目(2017~2019年)"太行山东麓人工增雨防雹作业技术试验"飞机和地面雷达观测数据,重点分析研究了2017年5月22日一次典型稳定性积层混合云对流泡和融化层的结构特征。研究结果表明,此次积层混合云高层存在高浓度大冰粒子,冰粒子下落过程中的增长在不同区域存在明显差异,在含有高过冷水含量的对流泡中,冰粒子增长主要是聚并和凇附增长,而在过冷水含量较低的云区以聚并增长为主。由于聚并增长形成的大冰粒子密度低,下落速度小,穿过0℃层时间更长,出现大量半融化的冰粒子,使融化现象更为明显。镶嵌在层状云中的对流泡一般处于0℃^-10℃(高度4~6 km)层之间,垂直和水平尺度约2 km,最大上升气流速度可达5 m s^-1。对流泡内平均液态水含量是周围云区的2倍左右,小云粒子平均浓度比周围云区高一个量级,大粒子(直径800μm以上)的浓度也更高。在具有较高过冷水含量的对流泡中降水形成符合"播撒-供给"机制,但在过冷水含量较低的区域并不符合这一机制。

Cloud microphysical process is one of the key processes in the formation of clouds and precipitation.However, little is known about the structure of convective region/convective bubble embedded in stratiform clouds. The characteristics of embedded convection and melting layer structure of a stable stratiform cloud with embedded convection on 22 May 2017 are investigated using aircraft and ground-based radar measurements. High concentration of large-size ice particles was found to exist in the upper part of the cloud, and the growth process of these ice particles varied in different areas when falling to lower levels. In the embedded convective bubble, ice particles grew mainly by aggregation and riming processes due to the existence of large content of supercooled liquid water;in clouds lacking supercooled liquid water, their growth was dependent on the aggregation process. As a result, the large-size ice particles formed by aggregation were of lower density and smaller falling velocity, and it took longer time for them to fall through the 0℃ layer. Thereby, more obvious melting phenomena were observed in these clouds than in the embedded convective clouds. The convections embedded in the stratiform cloud were generally located between 0℃-10℃(4-6 km altitude),with vertical and horizontal scales of about 2 km, and maximum updraft velocity of 5 m s^-1. In the embedded convective cells, the average liquid water content was about twice that in the surrounding clouds, the average concentration of small cloud particles was one order of magnitude higher than that in the surrounding clouds, and the concentration of large particles(diameter greater than 800 μm) was higher, too. Precipitation in embedded convections with high supercooled liquid water content took place through the"seeder-feeder"mechanism, which was not applied to precipitation in clouds with low supercooled liquid water content.