Methods of Modeling Radiant Energy Exchange in Radiation Fog and Clouds

This report describes several types of parameterizations commonly used in cloud and fog models to calculate the effects of radiant energy exchange in both the infrared and solar portions of the spectrum. The types of parameterizations used in several models of radiation fog have been summarized in the main text and detailed in the appendix, along with a few summaries of supporting studies. In general, the treatment of radiant exchange includes spectral resolution at the level of band models, whether band models are used explicitly or whether the radiation stream has been divided using a sum of exponentials approach. All of the studies use a plane parallel approximation in one form or another and all assume spherical particles for droplets and aerosols. The more sophisticated studies use a delta-two stream approach to account for the effects of multiple scattering. A few of the models include a prognostic equation that links the change in the microphysical distribution with the radiation field. The more advanced models also include a carefully designed surface flux exchange model. The strengths and deficiencies of the approaches are discussed and recommendations of a proper radiative parameterization are listed. Radiation fog models, Radiation parameterizations, Radiation models