Aircraft Observations of Ice Phase Microphysical Characteristics in Stratiform Clouds over the Qilian Mountains in Northwestern China

The ice-phase microphysical characteristics of a stratiform cloud system over the Qilian Mountains in northwestern China on 15 September 2022 were analyzed via aircraft data. The stratiform cloud system developed under southwesterly flows at 500 hPa and was affected locally by topography. Synoptic features and aircraft observations revealed strengthened cloud development on the leeward slope. The ice particle habits and microphysical processes at heights of 6–8 km were investigated. The cloud system was characterized by extremely low supercooled liquid water content at temperatures between -4°C and -17°C. The ice particle concentrations ranged predominantly from 10 to 30 L-1, corresponding to ice water content ranging from 0.01 to 0.05 g m-3. Active ice aggregation was observed at temperatures colder than -10°C. The windward side of the cloud system exhibited weaker development and two distinct cloud layers. Intense orographic uplift on the leeward slope enhanced ice particle aggregation. The clouds on the leeside presented lower ice particle concentrations but larger sizes than those on the windward side. The influence of aggregation on the ice particle size distribution was reflected in two main aspects. One aspect was the bimodal spectra at -16°C, with the first peak at 125 μm and subpeak at 400–500 μm; the other was the broadened size spectra at -13°C due to significant aggregation of dendrites.