Regulation of Cloud Particle Spectra and Vertical Structure by Sub-Cloud Aerosols: Insights from Aircraft Observations and Numerical Simulations

Abstract. Aerosol–cloud interactions are key processes affecting cloud microphysics, precipitation formation, and climate system energy balance. Using aircraft observations from Hebei and parcel model simulations, the spectral characteristics, vertical structures, and response of cloud particles to aerosols are systematically analysed. In liquid and mixed-phase clouds, droplet number concentration peaks occur at 5–7 μm and 14–15 μm, whereas ice and mixed-phase clouds exhibit ice crystal peaks near 125 and 1550 μm. Regarding ice crystals, high aerosol concentrations enhance number concentrations at both small and large sizes, whereas concentrations within the intermediate range are lower than those under low aerosol loadings. High sub-cloud aerosol loading effective droplet diameters in the lower part of liquid and mixed-phase clouds are 2.4 and 2.8 μm larger, respectively, than those in the upper part, accompanied by higher droplet number concentrations and broader size distributions. Under low-aerosol conditions, the upper part of liquid and mixed-phase clouds contains droplets that are 2.7 μm and 4.4 μm larger than those in the lower part, respectively. The droplet number concentrations are higher in the upper layers for both cloud types. In ice clouds, high sub-cloud aerosol concentrations yield decreasing ice crystal number concentrations with height and effective radius that first increase but then decrease. Sensitivity experiments reveal that increasing aerosol concentrations cause a monotonic increase in droplet number concentrations. At low aerosol concentrations. High aerosol concentrations amplify vapor competition and latent heat release, increasing temperature and reducing supersaturation, reducing the effective radius.