Phase characterization of cold sector southern ocean cloud tops: Results from SOCRATES

For a given cloud, whether the cloud top is predominately made up of ice crystals or supercooled liquid droplets plays a large role in the clouds overall radiative effects. This study uses collocated airborne radar, lidar, and thermodynamic data from 12 high-altitude flight legs during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) to characterize Southern Ocean (SO) cold sector cloud top phase (i.e., within 96 m of top) as a function of cloud top temperature (CTT). A training data set was developed to create probabilistic phase classifications based on High Spectral Resolution Lidar data and Cloud Radar data. These classifications were then used to identify dominant cloud top phase. Case studies are presented illustrating examples of supercooled liquid water at cloud top at different CTT ranges over the SO (-3 degrees C < CTTs < -28 degrees C). During SOCRATES, 67.4% of sampled cloud top had CTTs less than 0 degrees C. Of the subfreezing cloud tops sampled, 91.7% had supercooled liquid water present in the top 96 m and 74.9% were classified entirely as liquid-bearing. Liquid-bearing cloud tops were found at CTTs as cold as -30 degrees C. Horizontal cloud extent was also determined as a function of median cloud top height.