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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 5, issue 4 | Copyright
Geosci. Model Dev., 5, 989-1008, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Development and technical paper 03 Aug 2012

Development and technical paper | 03 Aug 2012

Coupling a new turbulence parametrization to RegCM adds realistic stratocumulus clouds

T. A. O'Brien1,*, P. Y. Chuang1, L. C. Sloan1, I. C. Faloona2, and D. L. Rossiter1 T. A. O'Brien et al.
  • 1University of California, Santa Cruz, Department of Earth and Planetary Sciences, Santa Cruz, California, USA
  • 2University of California, Davis, Department of Land, Air, and Water Resources, Davis, California, USA
  • *now at: Lawrence Berkeley National Lab, Berkeley, California, USA

Abstract. To model stratocumulus clouds in the regional climate model, RegCM4.1, the University of Washington (UW) turbulence parametrization has been coupled to RegCM. We describe improvements in RegCM's coastal and near-coastal climatology, including improvements in the representation of stratiform clouds. By comparing output from a 27-yr (1982–2009) simulation of the climate of western North America to a wide variety of observational data (station data, satellite data, and aircraft in situ data), we show the following: (1) RegCM-UW is appropriate for use in general regional climate studies, and (2) the UW model distinctly improves the representation of the marine boundary layer in RegCM. These model–data comparisons also show that RegCM-UW has a slight cold bias, a (wet) precipitation bias, a systematic low bias in the vertically-integrated liquid water content near the coast, and a high bias in the fractional cloud coverage. The model represents well the diurnal, monthly, and interannual variability in low clouds. These results show RegCM-UW as a nascent mesoscale stratocumulus model that is appropriate for stratocumulus investigations at scales ranging from hourly to decadal. The source code for RegCM-UW is publicly available, under the GNU license, through the International Centre for Theoretical Physics.

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