Simulating Closed-to-Open Mesoscale Cellular Convection Over the Southern Ocean: Part II. Perturbed Physics Experiments

Accurate representation of mesoscale cellular convective (MCC) cloud morphology over the Southern Ocean is essential for improving climate model parametrizations and reducing projection uncertainties given their highly variable radiative impacts. In this study, we investigate three potential drivers of the organization and transition from closed-to open-cell MCC clouds over the Southern Ocean under post-frontal conditions: (a) sea surface temperature (SST) including its gradients, (b) cloud ice production processes, and (c) microphysical latent cooling. Using a convection-permitting configuration of the WRF model and building on findings from Part I, we evaluate how each driver shapes the morphological evolution of MCCs. Perturbed physics experiments reveal that while SST is not the primary driver of the closed-to-open MCCs transition, it influences cloud cellular morphology in two ways: warmer SST deepens the boundary layer and enhances precipitation, whereas colder SST suppresses boundary layer mixing, leading to reduced cloud cover. Enhanced ice production plays a key role in MCCs organization, driving cloud “break-up” by increasing precipitation formation. Cloud evaporative cooling significantly affects MCCs organization, likely by affecting negative cloud buoyancy, allowing clouds to grow deeper and drying the boundary layer. These findings highlight critical processes that govern MCCs behavior and provide valuable insights for improving the representation of shallow clouds in climate models, ultimately aiding efforts to reduce uncertainties in climate sensitivity projections.