Daily Variation Law of Solar Radiation Flux Density Incident on theHorizontal Surface

The instantaneous solar radiation flux density incident on the horizontal surface near the ground, consisted of three sections, direct radiation, scattered radiation, and thermal radiation flowing down through the atmosphere, directly or indirectly comes from the sun. The dynamics of the solar radiation flux density incident on the horizontal surface near the ground influence all life processes and environment. In this study, the daily variation law of solar radiation flux density incident on the horizontal surface developed. The results showed that generally, sky conditions is stable, and the daily dynamic in the solar radiation flux density incident on the horizontal surface near the ground is the function of time, and can be described by a normal distribution model in a day. The main parameters of the model change with date and the meteorological conditions in a day.