Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. (2013) Parametrization of instantaneous global horizontal irradiance: clear-sky component Zhian Sun, a * Xianning Zeng, b Jingmiao Liu, c,d Hong Liang c and J. Li e a Centre for Australian Weather and Climate Research, Australian Bureau of Meteorology, Melbourne, Victoria, Australia b Nanjing University of Information and Technology Sciences, Nanjing, China c Chinese Academy of Meteorological Sciences, Beijing, China d Institute of Atmospheric Environment, China Meteorological Administration, Shenyang, China e Canadian Centre for Climate Modelling and Analysis, Science and Technology Branch, Environment Canada, University of Victoria, British Columbia, Canada *Correspondence to: Z. Sun, Australian Bureau of Meteorology 700 Collins Street Melbourne Victoria Australia 3001. E-mail: z.sun@bom.gov.au 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%. Copyright c  2013 Royal Meteorological Society Key Words: global horizontal irradiance; radiative transfer; transmittance; parametrization Received 4 June 2012; Revised 27 November 2012; Accepted 13 December 2012; Published online in Wiley Online Library Citation: Sun Z, Zeng X, Liu J, Liang H, Li J. 2013. Parametrization of instantaneous global horizontal irradiance: clear-sky component. Q. J. R. Meteorol. Soc. DOI:10.1002/qj.2126 1. Introduction Atmospheric radiative transfer is one of the most important physical processes in the Earth–atmosphere system. It determines the distribution of atmospheric radiative energy across the whole globe, which directly influences the variation of temperature, development of convection and the formation of clouds and rain. Therefore, a radiative transfer parametrization must be included in all climate models. There has been a large research effort in recent years aimed at enhancing the accuracy and efficiency of radiative transfer models (Murcray et al., 1995; Edwards and Slingo, 1996; Mlawer et al., 1997; Sun and Rikus, 1999; Li and Barker, 2005; Sun, 2011). However, because Copyright c  2013 Royal Meteorological Society