Ice Particle Size Distributions and Secondary Ice Production in Stratiform Clouds Over the Qilian Mountains in Northwestern China

Abstract The growth processes and size distributions of ice particles in two stratiform clouds over the Qilian Mountains in northwestern China were investigated. A comparison of the moist Froude number between the two cases suggested stronger cross‐barrier flow on 29 August than that on 16 August 2020, corresponding to relatively high precipitation amounts on 29 August. The stratiform cloud regions exhibited stable structures and dominated by vapor deposition. Convective regions contained more graupel, dendrites, and larger aggregates and grew primarily through riming and aggregation. Secondary ice production was responsible for the significant increase in ice particle concentrations in the convective region. Evidence of the Hallett–Mossop process was observed at temperatures between −3°C and −8°C and the estimated ice splinter production rate in the Hallett–Mossop region was positively related to the high ice particle concentration. Ice‐ice collisional fragmentation might coexist at approximately −4°C in the embedded convective region. The observed ice particle size distributions (PSDs) in stratiform regions were weakly dependent on temperatures ranging from −5°C to −18°C and exhibited bimodal distributions with breakpoints at 500–600 μm. The observed PSDs in convective regions were also bimodal, but exhibited varied peaks due to the variation of dominant microphysical processes. The incomplete gamma fitting technique effectively characterized the PSDs from 300 to 2,000 μm. The significant increase in N 0 due to high ice particle concentrations was possibly attributed to secondary ice production processes within clouds, and the decrease in λ corresponded to broadened ice particle spectra associated with aggregation.