Simulating Closed-to-Open Mesoscale Cellular Convection Over the Southern Ocean: Part I. Evaluation Using SOCRATES and CAPRICORN Observations

Understanding Earth's climate sensitivity remains a critical challenge for improving climate projections. Discrepancies between recent and previous generations of climate models highlight the need for better representation of low-level clouds over the Southern Ocean (SO)—a region with unique modeling challenges due to complex interactions among dynamics, microphysics, and radiation, compounded by a historical lack of in situ observations. This study evaluates the performance of a convection-permitting WRF model configuration during post-frontal conditions, using recent field campaign data and satellite observations for validation. Our results show that the simulation effectively reproduces the key morphological distinctions between closed and open mesoscale cellular convective clouds (MCC), aligning with both in situ and remote sensing data. The simulation captures the higher cloud cover in closed MCC regions (65%) with lower cloud top heights (1.3 km), compared to open MCC regions (46%) with higher cloud tops (2.3 km), consistent with field measurements. Additionally, the simulation reproduces qualitative differences in ice production and precipitation frequency between closed and open MCCs. However, particularly at higher latitudes, the simulation underestimates cloud cover and significantly underrepresents precipitation and ice production, likely due to limitations in the representation of ice production mechanisms. This research also sets the stage for further analysis of the processes driving the mesoscale organization and transitions between open and closed MCC states (Part II). The combined use of field observations, satellite data, and convection-permitting simulations provides a comprehensive framework for advancing our understanding of these cloud systems and their role in climate sensitivity.