Radiative transfer of infrared radiation in model clouds

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Abstract
The complete radiative transfer equation in its scalar form is evaluated to obtain the emissivity, transmissivity and reflectivity of model clouds at selected infrared wavelengths. The cloud models assume liquid water concentrations of 0.1 and 0.3 g/m3 which are thought to be representative of layer clouds and fogs of moderately low and high water contents. It is the purpose of this study to determine relative errors in radiative transfer calculations in the infrared which are introduced by choices of model cloud droplet size distributions. This task is accomplished by comparing differences in infrared cloud characteristics resulting from the use of the well-known droplet distribution functions of Best (1951), Diem (1948), Deirmendjian (1964) and occasionally that of Warner (1969) for the same liquid water content. The water vapor window, subdivided into 5 spectral intervals, and a spectral region of the strong 6.5 micron water vapor band are investigated in detail for this purpose. It is found that the exponential and unimodal distributions of Best, Diem and Deirmendjian yield results which differ non-critically in practically all cases. The bimodal distribution of Warner, which is used only in conjunction with the lower liquid water content, shows appreciable differences with respect to the other three distribution functions. Of the many computational results which are available, only a few representative samples are displayed. DOI: 10.1111/j.2153-3490.1971.tb00600.x

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