Abstract:

 Radiation calculations in global numerical weather prediction (NWP) and climate models are usually conducted in 3-hourly time interval in order to reduce the computational cost. Although great reduction in time consuming, this treatment can lead to an incorrect solar radiation at the Earth’s surface which could be one of the error sources in modeled surface energy budget, convection and precipitation. In order to improve the simulation of the diurnal cycle of the solar radiation, a fast scheme has been developed based on detailed radiative transfer calculations for a wide range of atmospheric conditions and can be used to determine the surface solar radiation at each model integration time step with affordable costs. This scheme is divided into components of clear-sky and cloudy-sky conditions. The cloudy-sky component is introduced in this paper. The results indicate that the input variables required by this scheme are all available in NWP and climate models or can be obtained from satellite observations. Therefore, the scheme can be used in a global model to determine the surface solar radiation. It can also be used as an offline scheme to calculate the surface radiation using data from satellite measurements. The scheme has been tested using observations obtained from three Atmospheric Radiation Measurements (ARM) stations established by the U. S. Department of Energy. The results show that a half hourly mean relative error of global solar radiation under all-sky conditions is less than 7%.

Key words: Global solar radiation, Atmospheric transmission, Cloud optical depth, Radiative parameterization