A case study of aircraft observations of ice cloud microphysical properties over the North China Plain: Vertical distribution, vertical airflow and aerosol - cloud effects

The study of particle nucleation and growth within clouds forms the fundamental microphysical component of cloud precipitation physics. Thus, we can establish cloud and fog precipitation development theories, providing a foundation for understanding weather, climate, and environmental changes. This case study, we observed ice cloud particles and meteorological elements using aircraft instruments over the North China Plain region on February 18, 2019. Focusing on aerosol-cloud interactions, we categorized clouds using altitude, vertical airflow, and cloud droplet concentration. The average number concentrations of cloud droplets (Nc), ice (Ni), and aerosols (Na) were 1.06 cm -3 , 5 .30 L -1 , and 1 .63 x 10 3 cm -3 , respectively. The ice water content (IWC) in clouds was two orders of magnitude higher than the liquid water content (LWC). The differences in Nc at different heights were primarily caused by the presence of small droplets (smaller than 15 mu m). Droplet concentrations were higher at 1-2 km and at the top of the clouds (5-6 km). Ice formation and growth was nonuniform in all zones, concentrated in the smallest and largest particle size ranges, with peaks at 125 and 1500 mu m. Updraft significantly impacted cloud droplets, promoting their development and growth through water vapor condensation. Vertical airflow exerted a minor impact on aerosols. The Wegener-Bergeron-Findeisen process, driven by ice supersaturation and cloud liquid water subsaturation, led to a decrease in cloud droplet concentration and an increase in ice crystal concentration within the updraft region. In regions with different cloud droplet enrichment levels, the distribution of particles varied within the clouds. Zone with no vertical movement exhibited higher Nc than zone with downdraft airflow. The dense cloud droplet zone with downdraft airflow indicated narrower spectrum. Nc ranged from 2.5 to 19 mu m, Ni ranged from 125 to 1350 mu m, and Na ranged from 0.1 to 1 mu m (no particles between 0.4 and 1 mu m were observed). Ice formation and growth varied in each zone, possibly due to ice fragmentation.