Approximation of the infra-red radiation flux in an atmosphere with cloud |
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| Authors: | M J Manton |
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| Institution: | (1) Division of Cloud Physics, CSIRO, Sydney, Australia |
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| Abstract: | Summary A three-stream infra-red radiation scheme for use particularly in boundary layer models is described. Local uniformity of the atmosphere (i.e. a generalization of the cooling to space approximation in clear air) is assumed, and the radiation equation is solved by simple collocation rather than by the full discrete ordinate method. In clear air the scheme corresponds to the usual approximation, which incorporates the Elsasser factor in the transmission function to account for diffuse radiation. The band models of Goody for water vapour and Elsasser for carbon dioxide are used for the band averaging of the transmission functions. Consistent with this, the band averaging of the radiation flux in cloud is undertaken by replacing the rapidly varying absorption coefficients for the gases by the actual band-averaged values of those coefficients. The band averaging is precise in the limits of strong and weak gaseous absorption. |
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| Keywords: | Infrared radiation Radiation transfer through clouds Radiation flux in the atmosphere |
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