Based on an accurate atmospheric radiative transfer scheme, a parametrization of instantaneous global horizontal irradiance (GHI) at the Earth's surface has been developed. The scheme is named SUNFLUX and this article describes the development of the scheme for clear-sky conditions. The work dealing with clouds has been published in a separate article. Unlike traditional methods, this study applies the band model idea used in radiative transfer theory to the development of the surface radiation scheme and, importantly, includes absorption and scattering in the parametrization. Thus the scheme is more accurate compared with those using simple empirical approaches and may be applied to any site without being tuned for local conditions. The parametrization of aerosol transmittance and albedo developed by Kokhanovsky et al. is adopted to account for the effects of aerosols. All variables used in the scheme are available in climate models or from satellite observations. Therefore, the parametrization can be used to determine the GHI at the surface under clear-sky conditions
The scheme is evaluated using observations obtained from three US Atmospheric Radiation Measurement (ARM) stations and three stations on the Tibetan Plateau, and the results demonstrate that the scheme is accurate. The relative mean bias difference is less than 4.3% and the relative root-mean-squared difference is less than 0.09%.