A method to compute solar radiation at surface in any time interval based on NCEP reanalysis

Diurnal variation of solar radiation at the Earth's surface is of importance to data assimilation, weather and climate model assessment. However, the shortage of solar radiation data has limited the use of other meteorological data. Solar radiation at a time of day can not be simply calculated by interpolation because it is strongly influenced by solar hour angle, cloud, water vapor, aerosols, and other factors, which brings great troubles to model applications. This paper presents a method to compute mean solar radiation at surface in any time interval and develops a data set of hourly mean solar radiation that can be used to assess models by use of NCEP 6-hourly mean of downward solar radiation flux at surface. Compared with measured hourly mean of solar radiation, the calculated hourly mean solar radiation agrees closely with observation in numerical value and variation trend. The calculated hourly-mean solar radiation reflects the diurnal variation all over the world and it can be used as land model forcing. It is helpful to simulation, validation and assessment of the weather and climate model and can make up the shortage of measured solar radiation data.