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Measured ice nucleating particle concentrations improve the simulation of mid-level mixed-phase clouds over the high-latitude Southern Ocean
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  • Étienne VIGNON,
  • Simon Peter Alexander,
  • Paul J DeMott,
  • Georgia Sotiropoulou,
  • Franziska Gerber,
  • Thomas C. J. Hill,
  • Roger T Marchand,
  • Athanasios Nenes,
  • Alexis Berne
Étienne VIGNON

Corresponding Author:etienne.vignon@epfl.ch

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Simon Peter Alexander
Australian Antarctic Division
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Paul J DeMott
Colorado State University
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Georgia Sotiropoulou
École polytechnique fédérale de Lausanne
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Franziska Gerber
WSL Institute for Snow and Avalanche Research SLF
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Thomas C. J. Hill
Colorado State University
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Roger T Marchand
University of Washington
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Athanasios Nenes
Ecole Polytechnique Federale de Lausanne
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Alexis Berne
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Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed-phase clouds. This study uses the remote-sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid-level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local circulation related to cloud-top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top-down convection to capture the turbulence-microphysics interplay at cloud top.