1MINES ParisTech, PSL Research University, O.I.E. – Centre Observation, Impacts, Energy – Sophia Antipolis, France
2Laboratoire de Météorologie Dynamique, IPSL/CNRS, UMR 8539, Ecole Polytechnique, France
*now at: Total New Energies, R&D – Solar, Paris la Défense, France
**now at: Reuniwatt, Sainte-Clotilde, Réunion, France
Received: 18 Feb 2014 – Discussion started: 01 Apr 2014
Abstract. In the case of infinite plane-parallel single- and double-layered cloud, the solar irradiance at ground level computed by a radiative transfer model can be approximated by the product of the irradiance under clear atmosphere and a modification factor due to cloud properties and ground albedo only. Changes in clear-atmosphere properties have negligible effect on the latter so that both terms can be calculated independently. The error made in using this approximation depends mostly on the solar zenith angle, the ground albedo and the cloud optical depth. In most cases, the maximum errors (95th percentile) on global and direct surface irradiances are less than 15 W m−2 and less than 2–5% in relative value. These values are similar to those recommended by the World Meteorological Organization for high-quality measurements of the solar irradiance. Practically, the results mean that a model for fast calculation of surface solar irradiance may be separated into two distinct and independent models, possibly abacus-based, whose input parameters and resolutions can be different, and whose creation requires less computation time and resources than a single model.
Revised: 23 Jun 2014 – Accepted: 03 Jul 2014 – Published: 14 Aug 2014
Please read the corrigendum first before accessing the article.
Oumbe, A., Qu, Z., Blanc, P., Lefèvre, M., Wald, L., and Cros, S.: Decoupling the effects of clear atmosphere and clouds to simplify calculations of the broadband solar irradiance at ground level, Geosci. Model Dev., 7, 1661-1669, doi:10.5194/gmd-7-1661-2014, 2014.