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Abstract
To follow the path of sunlight through the Earth system, one needs consider attenuation, scattering, absorption, refraction and reflection throughout the atmosphere, ocean, cryosphere, and land surface, plus the wavelength dependence of these radiative transfer (RT) processes. This RT problem includes gases, surfaces, and aerosols (clouds). Using Solar-J as a flexible RT code, we build a benchmark code for solar radiation using RT components that are more accurate than typical approximations used in the operational solar heating codes. Using a range of versions of Solar-J, we identify and evaluate the errors in RT approximations by integrating over realistic global atmospheric conditions taken from a weather forecast model. Solar-J was built on a photochemistry model at short wavelengths attached to the gas-phase absorption model from RRTMG-SW for wavelengths greater than 0.6 microns. In this study, we assess separately the errors in each of the following approximations with the goal of identifying which improvements are highest priority for the next generation of solar radiation modules in Earth system models:
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