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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 102, NO. D12,
PAGES 13,527–13,534,
1997
A modeling study of the effect of drizzle on cloud optical depth and susceptibility
Graham Feingold
Cooperative Institute for Research in the Atmosphere and NOAA Environmental Technology Laboratory Boulder, Colorado
Reinout Boers
Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia
Bjorn Stevens
Department of Atmospheric Science, Colorado State University, Fort Collins
William R. Cotton
Department of Atmospheric Science, Colorado State University, Fort Collins
Abstract
This paper examines the impact of drop spectral broadening, generated by the collection process, on the optical depth, cloud
albedo, and susceptibility of marine stratocumulus clouds. The results are arrived at using (1) the output from a simple box
model calculation of collection and (2) the output from an eddy-resolving model of stratocumulus clouds that explicitly represents
the size distribution of the drops. It is shown that commonly used relationships for cloud optical properties developed for
narrow spectra do not generally apply to spectra undergoing spectral broadening. The optical depth dependence on the drop
number concentration to the one-third power is shown to be an overestimate of the optical depth when spectra broaden through
collection. In addition, the cloud susceptibility dependence on drop number is shown to be larger for spectra experiencing
broadening than for narrow spectra.
Received 20
November
1996;
accepted 26
March
1997.
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Citation: Feingold, G., R. Boers, B. Stevens, and W. R. Cotton
(1997),
A modeling study of the effect of drizzle on cloud optical depth and susceptibility,
J. Geophys. Res.,
102(D12),
13,527–13,534.
Copyright 1997 by the American Geophysical Union.
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