Characterization of Southern Ocean Boundary Layer Clouds Using Airborne Radar, Lidar, and In Situ Cloud Data: Results From SOCRATES

Climate and numerical weather prediction models struggle to accurately predict radiative forcing over the Southern Ocean (SO), as the amount of clouds and their phases are poorly represented in such models due to a lack of observations upon which to base parameterizations. To address this, a novel particle identification (PID) scheme, based upon airborne radar and lidar data, was applied to data collected during the Southern Ocean Clouds, Aerosol, Radiation Transport Experimental Study (SOCRATES) to assess the vertical structure of SO boundary layer clouds. A comparison between the PID scheme and in situ phase data from SOCRATES showed relatively good agreement between the two data types. The convectivity of the clouds sampled during SOCRATES was determined using the novel Echo Classification from COnvectivity for Vertically pointing radars product. The PID and in situ data were then used synergistically to identify the following features of cloud vertical structure: (a) Supercooled liquid water was very common (Probability, P ∼ 80%) at cloud top for convective and stratiform clouds; (b) Supercooled large drops with maximum dimensions >95 μm frequently appear within a hundred meters below cloud top, particularly within convective clouds (Max P 35%–45%), but also within stratiform clouds (Max P 20%–30%); (c) Ice production was associated with convective activity, with P ∼ 20% at cloud top, increasing to 50%–70% 200 m below top, compared to P < 30% everywhere in stratiform clouds; (d) Convective clouds were found to be more vertically heterogeneous than stratiform clouds.