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

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.