The preparation of hourly weather data generally requires that the diffuse solar radiation on a horizontal surface be determined by calculation based on the global solar radiation. Many factors are involved that determine the magnitude of the diffuse portion of the global radiation. This paper analyzes the effect of ground snow cover and solar altitude angle on the relationship. Relationships are presented that permit the calculation of diffuse solar radiation, taking into account the solar altitude angle and the "snow" or "no-snow" ground cover for various values of the clearness index. Since the WYEC hourly weather tapes are in the TRY fonnat with a snow cover flag, the calculation of the diffuse solar based on these relationships can be easily carried out.

Units: SI