Seasonal Variability of Warm Boundary Layer Cloud and Precipitation Properties in the Southern Ocean

The extensive cloudiness and resulting high albedo of the Southern Oceans (SO) are predominantly due to the occurrence of widespread marine boundary layer clouds.    Recent work finds correlations between biogenically enhanced cloud condensation nuclei concentrations and cloud droplet number concentrations derived from passive satellite data. The active remote sensors in the A-Train have created a unique and long-term record of these clouds that include vertical profiles of radar reflectivity and microwave brightness temperature from CloudSat that can be combined with solar reflectances from MODIS.  We examine this data record using a unique algorithm to infer warm-topped cloud and precipitation properties.  We find seasonal variations in cloud properties of summer season clouds demonstrating higher cloud droplet number concentrations on average.  In addition, a given rain rate requires higher liquid water contents in summer suggesting that the precipitation in summer clouds are more susceptible to changes in droplet number compared to similar clouds during winter.  These results will be examined in light of a recently collected ship-based remote sensing data set collected during a five-week cruise into the SO by the Ausralian Research Vessel Investigator as part of the Capricorn Project.