Precipitation in Stratocumulus Clouds: Observational and Modeling Results

The spatial and temporal variability of precipitating stratocumulus layers is examined using aircraft observations, satellite retrievals of cloud optical depth, and one-dimensional models that include coalescence and a simple representation of layer turbulence. The aircraft observations show large horizontal variations in cloud thickness and precipitation, with local rain rates 4–5 times larger than the replacement moisture flux, and evidence for precipitation scavenging of small cloud droplets. The satellite observations show that, despite this local water loss, the distribution of cloud optical thickness remains nearly constant over the course of a day, indicating that on larger scales precipitation removal and cloud-top entrainment are in approximate balance with the vapor flux. The authors apply analytic and numerical models of steady-state precipitation to the observed microphysical conditions, and find that the models can match the drop size distributions observed during both heavy and light stratocumulus rainfall, but are especially sensitive to the processes governing the growth rate of the smallest drizzle drops. Copyright 1995 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyright@ametsoc.org.Science, Faculty ofEarth and Ocean Sciences, Department ofReviewedFacult