Influence of Heterogeneous Ice Nucleation of Sea Spray Aerosol on Southern Ocean Clouds in theNCAR Community Atmosphere Model

The Southern Ocean (SO) is one of the cloudiest regions on earth, with wide spatial coverage of persistent supercooled liquid clouds, including stratocumulus and frontal cloud systems. The SO region is a region of persistent and common radiation biases in many climate models, likely due to simulated mixed phased clouds containing excessive ice, thereby leading to shortened cloud lifetimes and/or brighter clouds. Aerosol-cloud interactions occurring in mixed phase clouds over the SO are hypothesized to be largely controlled by the cloud properties of sea spray aerosol (SSA) due to a lack of terrestrial aerosol sources. This aspect is particularly unique for primary ice nucleation, where observations indicate that the ice nucleation ability of SSA is at minimum two orders of magnitude less active than terrestrial sources (e.g., mineral dust). It is therefore hypothesized that improvements to the primary ice nucleation scheme in a global climate model (the Community Atmospheric Model, CAM) will result in a decreased radiative bias due to clouds over the SO. While improvements to CAM have been made in the most recent version (CAM6), representation of the uniquely low ice nucleation ability of SSA is still lacking and the SO cloud phase partitioning has not been thoroughly evaluated against observations. Observations from the 2018 Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) field campaign, including remote sensing and in situ measurements of aerosol cloud activation properties, cloud phase and structure, are used to evaluate results from a suite of nudged CAM model simulations. Nudged simulations designed to investigate the role of differing primary ice nucleation schemes and cloud parameterizations (unified versus cloud type-specific) on simulated cloud phase will be presented.