The atmosphere above the Southern Ocean (SO) has very high cloud coverage, with the fraction of clouds below 3 km in altitude approaching 80% (Haynes et al., 2011;Mace et al., 2009). Many of these low boundary layer (BL) clouds are associated with large and complex extratropical cyclones that are prevalent over the SO (McFarquhar et al., 2021), and are one of the largest sources of disagreement among General Circulation Models (GCMs) (Bony et al., 2006;Vial et al., 2013). An understanding of the processes responsible for the complicated structure of SO BL clouds is critical for improving the parameterizations that are used to represent such processes in GCMs that model cloud radiative feedbacks in a rapidly warming global climate (McCoy et al., 2015;Trenberth & Fasullo, 2010), as needed to better project future climate change (IPCC, 2021).Past studies have shown that supercooled liquid water (SLW; liquid water at subfreezing temperatures) is especially common in SO clouds, and more prevalent than at similar latitudes in the Northern Hemisphere (NH), likely due to the lack of ice nucleating particles, which tend to increase glaciation rates, over the SO (Gong