Simulation of Cloud Processes Over Offshore Coastal Antarctica Using the High-Resolution Regional UK Met Office Unified Model With Interactive Aerosols

Price, R. ORCID: https://orcid.org/0000-0003-1981-9860; Orr, A. ORCID: https://orcid.org/0000-0001-5111-8402; Field, P.F.; Mace, G.; Protat, A.. 2025 Simulation of Cloud Processes Over Offshore Coastal Antarctica Using the High-Resolution Regional UK Met Office Unified Model With Interactive Aerosols. Journal of Geophysical Research: Atmospheres, 130 (4), e2024JD042109. 16, pp. 10.1029/2024JD042109

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Abstract/Summary

The Southern Ocean and offshore coastal Antarctica are key regions for global climate. Low level mixed-phase clouds strongly control the surface radiation budget of this region but remain challenging for climate models because of the complex processes controlling the sources and sinks of cloud liquid water, including both cloud liquid water and ice crystals. Here, we examine these interactions using the Unified Model (UM) regional climate model, with the Cloud AeroSol Interacting Microphysics (CASIM) and UK Chemistry and Aerosol (UKCA) models included for interactive aerosol and cloud microphysics. We simulate two case studies from the second field campaign of Clouds Aerosols Precipitation Radiation and atmospheric Composition over the Southern Ocean Phase 2 (CAPRICORN-2), which represent the open ocean and the offshore coastal region of Antarctica. Compared with these observations, we find that the UM underestimates surface aerosol concentration by up to an order of magnitude and investigate the effect of this bias on the simulated cloud microphysical and radiative properties. We find that the cloud liquid water path (LWP) and surface radiative fluxes are also biased in the offshore coastal Antarctic case study, with a 32% mean underestimation of LWP and 76% mean overestimation of downwelling surface shortwave flux. Sensitivity tests show that the cloud liquid water bias is largely caused by deficiencies in the representation of the meteorology, and less by aerosol or cloud microphysical properties. Our results provide key insights on the modeling of cloud processes in high southern latitudes.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1029/2024JD042109
ISSN:	2169-897X
Additional Keywords:	clouds aerosol Southern Ocean modeling
Date made live:	18 Feb 2025 10:19 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537791

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