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JOURNAL OF THE ATMOSPHERIC SCIENCES 49, 749-761, 1992
Solar radiative fluxes for broken cloud fields above reflecting surfaces
H. W. Barker, J. A. Davies
Abstract
A statistical bidirectional method for including the effects of underlying reflecting surfaces in Monte Carlo simulations
of atmospheric photon transport is presented. It is illustrated for the idealized Lambertian surface and a general
particulate surface. It is shown that the simple Lambertian surface should be an adequate approximation (to mildly
anisotropic surfaces) for calculation of overall fluxes for broken cloud fields. The problem of incorporating multiple
internal reflections of solar radiation between cloud and surface is reviewed, and cloud field reflectances to upwelling
radiation r(k) as a function of the number of internal reflections k are calculated. Unlike plane-parallel and regular
arrays of cloud, all r(k) are generally not equal for more realistic scaling cloud fields. Strictly speaking, this prohibits
use of the familiar geometric sum formulas for flux calculation in a multiple reflecting system. Fortunately, though fortuitously,
the geometric sum formulas can be used in such cases if all r(k) are assumed to equal approximately the spherical albedo of the
cloud field.
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