Simulating aerosol and cloud properties over coastal Antarctica in a high resolution regional model

Global climate models and reanalysis products have revealed large downwelling shortwave radiation biases over the Southern Ocean and Antarctica. The biases are hypothesized to be caused by the incapability of models to accurately simulate the frequent occurrence of low-level mixed-phase clouds in these regions. It’s crucial to elucidate the intricacy of cloud microphysics and aerosol-cloud interaction in climate models over the Southern Ocean and Antarctica in order to better simulate the climate system.

In this study, we use the ground-based observations colleted at Davis, East Antarctica to assess the capability of the high-resolution regional Unified Model (UM) to reproduce precipitating clouds off coastal Antarctica. We found the default configuration of the model can generally simulate the phase, vertical structure, and timing of clouds while exhibiting biases in the simulated water path and surface radiation fluxes compared to observations. A series of sensitivity tests with changed cloud and aerosol properties were conducted. The key findings suggest that: (1) Current monthly aerosol climatology implemented in the UM for cloud droplet activation largely underestimates aerosol concentrations, leading to fewer cloud droplets and worse radiation biases; (2) Increasing the cloud droplet number concentrations to a maximum satellite-based value doesn’t have a significant impact on liquid water path (LWP) and radiation biases; (3) A more realistic ice nucleating particle parameterization significantly increases the LWP and reduces temperature and radiation biases at coastal Antarctica. Moreover, preliminary results from coupling CASIM and GLOMAP aerosol schemes in the UM evaluated with ship-based observations over high-latitude Southern Ocean will be presented.