Abstract
A single-column model intercomparison of a heavily drizzling stratocumulus-topped boundary layer
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Max Planck Institute for Meteorology, Hamburg, Germany
Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
Japan Meteorological Agency, Tokyo, Japan
Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
Met Office, Exeter, UK
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Koninklijk Nederlands Meteorologisch Instituut, De Bilt, Netherlands
Department of Applied Mathematics, University of Washington, Seattle, Washington, USA
NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
NASA Goddard Institute for Space Studies, New York, New York, USA
This study presents an intercomparison of single-column model simulations of a nocturnal heavily drizzling marine stratocumulus-topped boundary layer. Initial conditions and forcings are based on nocturnal flight observations off the coast of California during the DYCOMS-II field experiment. Differences in turbulent and microphysical parameterizations between models were isolated by slightly idealizing and standardizing the specification of surface and radiative fluxes. For most participating models, the case was run at both typical operational vertical resolution of about 100 m and also at high vertical resolution of about 10 m. As in prior stratocumulus intercomparisons, the simulations quickly develop considerable scatter in liquid water path (LWP) between models. However, the simulated dependence of cloud base drizzle fluxes on LWP in most models is broadly consistent with recent observations. Sensitivity tests with drizzle turned off show that drizzle substantially decreases LWP for many models. The sensitivity of entrainment rate to drizzle is more muted. Simulated LWP and entrainment are also sensitive to the inclusion of cloud droplet sedimentation. Many models underestimate the fraction of drizzle that evaporates below cloud base, which may distort the simulated feedbacks of drizzle on turbulence, entrainment, and LWP.
Received 12 February 2007; accepted 2 August 2007; published 27 December 2007.
Citation: (2007), A single-column model intercomparison of a heavily drizzling stratocumulus-topped boundary layer, J. Geophys. Res., 112, D24204, doi:10.1029/2007JD008536.
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