Abstract
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.