Reflection and transmission of solar light by clouds: asymptotic theory A. A. Kokhanovsky1 and T. Nauss2 1Institute of Remote Sensing, University of Bremen, O. Hahn Allee 1, 28334 Bremen, Germany 2Laboratory of Climatology and Remote Sensing, Marburg University, Deutschhausstr. 10, 35032 Marburg, Germany
Abstract. The authors introduce a radiative transfer model CLOUD for
reflection, transmission, and absorption characteristics of
terrestrial clouds and discuss the accuracy of the approximations
used within the model. A Fortran implementation of CLOUD is
available for download. This model is fast, accurate, and capable
of calculating multiple radiative characteristics of cloudy media
including the spherical and plane albedo, reflection and
transmission functions, absorptance as well as global and diffuse
transmittance. The approximations are based on the asymptotic
solutions of the radiative transfer equations valid at cloud
optical thicknesses larger than 5.
While the analytic part of the solutions is treated in the code in an
approximate way, the correspondent reflection function (RF) of a
semi-infinite water cloud R∞ is calculated using numerical
solutions of the radiative transfer equation in the assumption of
Deirmendjian's cloud C1 model. In the case of ice clouds, the fractal ice
crystal model is used. The resulting values of R∞ with respect to
the viewing geometry are stored in a look-up table (LUT).
The results obtained are of importance for quick estimations of
main radiative characteristics of clouds and also for the solution
of inverse problems.
Citation: Kokhanovsky, A. A. and Nauss, T.: Reflection and transmission of solar light by clouds: asymptotic theory, Atmos. Chem. Phys., 6, 5537-5545, doi:10.5194/acp-6-5537-2006, 2006.