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Plane parallel biases for atmospheric reflectance and transmittance in the Arctic |
NRC/NASA GSFC (also Institute of Oceanology PAS, Poland),
NASA Goddard Space Flight Center
Results are presented of Monte Carlo simulations of the expected influence of nonuniform cloud structure and nonuniform surface albedo on radiative fluxes in the Arctic atmosphere. In particular, the plane parallel biases in cloud albedo and transmittance are studied. The bias is defined as the difference between the real cloud albedo or transmittance (i.e. nonuniform conditions) averaged over a given area, and the uniform or plane parallel case with the same mean cloud optical thickness and the same mean surface albedo. Ranges of means and standard deviations of the input parameters typical of Arctic conditions are obtained from the SHEBA experiment. The dependance of the biases is analysed with respect to the following: domain averaged values of the cloud optical thickness and suface albedo, scales of their spatial variabilities, shapes of the surface reflectance functions, presence of a scattering layer under the clouds and the solar zenith angle.
