We demonstrate that the temporal correlation between the abundance of particulate surface area at sea-level and measurements of ceilometer backscatter can be used to quantify boundary layer mixing. Throughout an austral summer voyage to the Ross Sea, correlations between the two quantities were consistently high, identifying that the Southern Ocean boundary layer was frequently well-mixed. This provides indirect evidence that the optical characteristics of low-level Southern Ocean cloud are fundamentally related to the abundance and physicochemical properties of boundary layer particles. Following this analysis, we define simple criteria for which the boundary layer is likely to be well-mixed. We found that if sea-level wind speeds exceeded 8 m/s or if the near-surface air was 3 K cooler than the sea surface, a well-mixed boundary layer was always observed. Overall, these conditions are satisfied 92% of the time between 40-70 S based on forecasts from the Antarctic Mesoscale Prediction System.