A modeling study of the effect of drizzle on cloud optical depth and susceptibility

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.

[1]  S. Twomey.  The Influence of Pollution on the Shortwave Albedo of Clouds , 1977 .

[2]  S. Twomey,et al.  Aerosols, clouds and radiation , 1991 .

[3]  P. Mason,et al.  Atmospheric flow over a succession of nearly two‐dimensional ridges and valleys , 1984 .

[4]  C. Bohren.  Multiple scattering of light and some of its observable consequences , 1987 .

[5]  S. Twomey.  Pollution and the Planetary Albedo , 1974 .

[6]  R. Pincus,et al.  Effect of precipitation on the albedo susceptibility of clouds in the marine boundary layer , 1994, Nature.

[7]  A. Betts,et al.  A cloudiness transition in a marine boundary layer , 1990 .

[8]  C. Moeng.  Large-Eddy Simulation of a Stratus-Topped Boundary Layer. Part I: Structure and Budgets , 1986 .

[9]  S. Twomey,et al.  Determining the Susceptibility of Cloud Albedo to Changes in Droplet Concentration with the Advanced Very High Resolution Radiometer , 1994 .

[10]  A. B. Long.  Solutions to the Droplet Collection Equation for Polynomial Kernels , 1974 .

[11]  B. Stevens,et al.  Numerical simulations of stratocumulus processing of cloud condensation nuclei through , 1996 .

[12]  S. Twomey,et al.  The nuclei of natural cloud formation part II: The supersaturation in natural clouds and the variation of cloud droplet concentration , 1959 .

[13]  George A. Isaac,et al.  The relationship between cloud droplet number concentrations and anthropogenic pollution : observations and climatic implications , 1992 .

[14]  D. Lilly,et al.  Modeling of Stratocumulus Cloud Layers in a Large Eddy Simulation Model with Explicit Microphysics. , 1995 .

[15]  Robert Pincus,et al.  Precipitation in Stratocumulus Clouds: Observational and Modeling Results. , 1995 .

[16]  G. L. Stephens,et al.  Radiation Profiles in Extended Water Clouds. I: Theory , 1978 .

[17]  C. Bretherton,et al.  Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, Drizzle, Surface Fluxes, and Entrainment , 1995 .

[18]  M. King,et al.  Determination of the optical thickness and effective particle radius of clouds from reflected solar , 1990 .

[19]  W. Hall,et al.  A Detailed Microphysical Model Within a Two-Dimensional Dynamic Framework: Model Description and Preliminary Results , 1980 .

[20]  W. Cotton,et al.  The Relationship between Drop In-Cloud Residence Time and Drizzle Production in Numerically Simulated Stratocumulus Clouds , 1996 .

[21]  A. Slingo.  A GCM Parameterization for the Shortwave Radiative Properties of Water Clouds , 1989 .

[22]  C. Fairall,et al.  Measurement of Stratus Cloud and Drizzle Parameters in ASTEX with a K , 1995 .

[23]  B. Stevens,et al.  Elements of the microphysical structure of numerically simulated nonprecipitating stratocumulus , 1996 .

[24]  R. Charlson,et al.  Bistability of CCN concentrations and thermodynamics in the cloud-topped boundary layer , 1990, Nature.

[25]  C. Bretherton,et al.  The Atlantic Stratocumulus Transition Experiment - ASTEX , 1995 .

[26]  B. Albrecht.  Effects of precipitation on the thermodynamic structure of the trade wind boundary layer , 1993 .

[27]  H. Gerber,et al.  Microphysical and short‐wave radiative structure of wintertime stratocumulus clouds over the Southern Ocean , 1996 .

[28]  R. Chervin,et al.  Global distribution of total cloud cover and cloud type amounts over the ocean , 1988 .

[29]  S. Nicholls.  The dynamics of stratocumulus: Aircraft observations and comparisons with a mixed layer model , 1984 .

[30]  G. Feingold,et al.  An Efficient Numerical Solution to the Stochastic Collection Equation , 1987 .

[31]  Stephen Nicholls,et al.  Observations of marine stratocumulus clouds during FIRE , 1988 .