Quantifying Susceptibility in aerosol and updraft limited regimes for Warm and Mixed-Phase Clouds Using LES

Clouds cover a large fraction of the Earth’s surface and play a central role in regulating Earth’s radiative balance, precipitation, and the global water cycle. Aerosols influence cloud formation by acting as cloud condensation nuclei (CCN), thereby modifying cloud microphysical and dynamical processes. However, the extent to which aerosol perturbations and dynamical factors influence cloud susceptibility (β = ∂lnN_d/∂lnN_a , where N_d is cloud droplet number concentration and N_a is aerosol number concentration) across different cloud types remains uncertain. In this study, we employ Large Eddy Simulations (LES) to quantify aerosol susceptibility in marine liquid phase stratocumulus and mixed-phase clouds. Two sets of simulations are performed: (i) simulations with increasing aerosol number concentrations (65, 100, 500, 1000, and 10 000 cm⁻³) as reference case, and (ii) simulations with enhanced updraft velocities for the same range of aerosol concentrations. For liquid-phase clouds, the susceptibility decreases from 1 to 0.78, 0.69, and 0.2 with increasing aerosol concentration, indicating a transition from an aerosol-limited to an updraft-limited regime. For enhanced updraft cases, the susceptibility decreases from 1, 0.84, 0.71, and 0.34. Increasing the updraft velocity enhances supersaturation, leading to increased activation of aerosols into cloud droplets compared to the reference case. As a result, at higher aerosol concentrations, the susceptibility is higher than in the reference case. Thus, the comparison between the reference and enhanced-updraft simulations indicates a transition from updraft-limited to aerosol-limited behaviour at high aerosol concentrations. Ongoing simulations of mixed-phase clouds also aim to quantify aerosol susceptibility in different dynamical regimes and assess how cloud phase influences aerosol-cloud interactions.