The impact of mixed-phase cloud processes on simulating Southern Ocean clouds and their radiative effect

Smith, Daniel K. E., Renfrew, Ian A., van den Heuvel, Floortje, Lachlan-Cope, Thomas, Crawford, Ian, Bower, Keith, Flynn, Micheal, Evans, Matthew D., Abel, Steven J. and Field, Paul (2025) The impact of mixed-phase cloud processes on simulating Southern Ocean clouds and their radiative effect. Journal of Geophysical Research: Atmospheres, 130 (23). ISSN 2169-897X

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Abstract

Over the Southern Ocean, atmospheric and climate models have large biases in their radiative fluxes, primarily caused by the representation of supercooled liquid and mixed-phase low-level clouds, both at the macro- and micro-scale. The radiation biases lead to errors in simulated sea surface temperature, sea ice properties and large-scale atmospheric circulation. We assess the performance of a convection-permitting configuration of the Met Office Unified Model (MetUM) in simulating cloud over the Southern Ocean. We utilise aircraft and satellite observations from several cases in February 2023 during the Southern Ocean Clouds (SOC) field experiment. We investigate the representation of three mixed-phase characteristics, namely ice nucleating particles (INP), the droplet number concentration and the spatial distribution of liquid and ice in mixed-phase clouds. A lower temperature-dependent INP concentration (based on synchronous INP measurements) results in lower ice mass and number concentrations that are closer to observations, and a higher cloud liquid water content. This reduces the net surface cloud radiative effect by up to 14 W m-2. Reducing the droplet number to the campaign average had a similar sized impact on the cloud radiative effect (up to 22 W m-2) but opposite in sign, highlighting these compensating errors. Similarly, changing how well mixed the clouds are leads to a large sensitivity in the cloud radiative effect (up to 31 W m-2). All three mixed-phase processes play a crucial role in correctly modelling mixed-phase clouds and their impact on the radiation budget over the Southern Ocean.

Item Type:	Article
Additional Information:	Data Availability Statement: The Southern Ocean Clouds aircraft observations will be made available on https://data.ceda.ac.uk/badc. The ice nucleation particle measurements are available at van den Heuvel et al. (2025). The CERES SSF is available from https://ceres.larc.nasa.gov/data/. The ACESPACE ice nucleating particle observations are available at Tatzelt et al. (2020). Owing to intellectual property rights restrictions, we cannot provide the source code or documentation papers for the UM. The MetUM is available for use under license. A number of research organizations and national meteorological services use the UM in collaboration with the Met Office to undertake basic atmospheric process research, produce forecasts, and develop the UM code. To apply for a license, see http://www.metoffice.gov.uk/research/modelling-systems/unified-model. CASIM is open source (BSD3 license) and it is available from https://code.metoffice.gov.uk, which requires registration. MetUM was run using Rose Suite Number u-cz325. The processed MetUM output is available at Smith (2025). Funding information: The Southern Ocean Clouds project was supported by the Natural Environment Research Council (NERC) as part of the CloudSense Programme and it was funded by the project Grant NE/T006404/1.
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User:	LivePure Connector
Date Deposited:	27 Nov 2025 12:30
Last Modified:	27 Nov 2025 12:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101122
DOI:	10.1029/2025JD044452

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