How meteorological conditions influence aerosol-cloud interactions under different pollution regimes

Aerosol-cloud interactions (ACI) involve quite complex physical and dynamical mechanisms, in which meteorological conditions play a crucial role. To investigate how the meteorological conditions impact ACI under different pollution regimes (polluted and clean) for marine liquid-phase clouds, the simulations are conducted using the chemistry version of Weather Research and Forecasting Model coupled with spectral-bin cloud microphysics. Our results indicate that, marine liquid-phase clouds transition from being updraft-driven to cold-advection-driven as lower tropospheric stability (LTS) increases. The enhancement of these clouds by aerosols intensifies with LTS, highlighting the dominant role of cold advection on wintertime clouds. Aerosols prolong cloud lifetime in moist environments and shorten it in dry environments. They generally suppress precipitation but can enhance it during some intense cloud processes by promoting cloud vertical development and collision-coalescence. The influences of meteorological conditions on ACI exhibit distinct differences between the two pollution regimes. Under the clean regime, activation efficiency shows low sensitivity to meteorological conditions, enabling aerosols in clouds to fully activate across most environments, while the aerosol-limited state and the dominance of condensation lead to increases in cloud droplet size, cloud liquid water path, and rainwater path with supersaturation. In contrast, under the polluted regime, ACI are more sensitive to relative humidity than under the clean regime, and clouds respond oppositely to aerosols under different LTS conditions. Additionally, the dominance of collision-coalescence leads to initial cloud intensification followed by weakening with supersaturation.