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Simulating Observations of Southern Ocean Clouds and Implications for Climate
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  • Andrew Gettelman,
  • Charles Bardeen,
  • Christina S. McCluskey,
  • Emma Järvinen,
  • Jeffrey Stith,
  • Chris Brethenton
Andrew Gettelman
National Center for Atmospheric Research (UCAR)

Corresponding Author:andrew@ucar.edu

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Charles Bardeen
National Center for Atmospheric Research (UCAR)
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Christina S. McCluskey
National Center for Atmospheric Research
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Emma Järvinen
Karlsruhe Institute of Technology
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Jeffrey Stith
National Center for Atmospheric Research (UCAR)
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Chris Brethenton
University of Washington
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Southern Ocean (SO) clouds are critical for climate prediction. Yet, previous global climate models failed to accurately represent cloud phase distributions in this observation-sparse region. In this study, data from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES) experiment is compared to constrained simulations from a global climate model (the Community Atmosphere Model, CAM). Nudged versions of CAM are found to reproduce many of the features of detailed in-situ observations, such as cloud location, cloud phase and boundary layer structure. The simulation in the latest versions of the model has improved its representation of SO clouds with adjustments to the ice nucleation and cloud microphysics schemes that permit more supercooled liquid. Initial comparisons between modeled and observed hydrometeor size distributions suggest that the modeled hydrometeor size distributions are close to observed distributions, which is remarkable given the scale difference between model and observations. Comparison to satellite observations of cloud physics is difficult due to model assumptions that do not match retrieval assumptions. Some biases in the model’s representation of SO clouds and aerosols remain, but the detailed cloud physical parameterization provides a basis for process level improvement and direct comparisons to observations. This is critical because cloud feedbacks and climate sensitivity are sensitive to the representation of Southern Ocean clouds.
16 Nov 2020Published in Journal of Geophysical Research: Atmospheres volume 125 issue 21. 10.1029/2020JD032619