Sensitivity of mixed-phase cold-air outbreak clouds to aerosol-cloud interactions and ice production processes depends on environmental conditions: a comparison between spring and autumn CAO case studies over the Labrador Sea

Aerosol-cloud interactions and ice production processes are important uncertainties in models of mixed-phase cold-air outbreak (CAO) clouds, which are vital for the estimation of cloud-phase feedback. Our model simulation results show that the sensitivities of the mixed-phase cloud properties during the two selected CAO cases are different, with Ice Nucleating Particle (INP) concentrations having a strong influence for both case studies, but the cloud droplet number concentration and the HM (Hallett-Mossop) efficiency only affect the warmer case. We also find that the simulations showing the best performance compared to observations are not consistent across multiple satellite-observed cloud properties, which suggests a possible structural deficiency in the model. The two cases are CAO events over the Labrador Sea, 15 March 2022 and 24 October 2022, with the latter one coinciding with the M-Phase aircraft campaign. The regional Met Office Unified Model coupled with a two-moment microphysics scheme was used to quantify the sensitivity of cloud cover, stratocumulus-to-cumulus transition, and cloud radiative properties to cloud droplet number concentration, INP concentration and efficiency of the HM process. Recent studies have aimed to understand how these two aspects influence CAO clouds, but have not compared the sensitivities under different environmental conditions or with a realistic temperature-dependent parameterisation for INPs. This study provides an instructive perspective on how cloud microphysics affects mixed-phase CAO clouds under different environmental conditions, and serves as a good basis for exploring the whole uncertain cloud microphysics parameter space across a range of environmental conditions.