THE FREQUENCY-DISTRIBUTION OF INSTANTANEOUS INSOLATION VALUES

The frequency distribution of instantaneous insolation values based on measurements carried out over a one-year period has been evaluated. The resulting fractional time distribution curves for instantaneous radiation are found to differ from that obtained previously for daily values. The instantaneous fractional time curves exhibit a distinct step associated with the predominance of two radiation states, clear and cloudy. A model derived from the concept of Boltzmann statistics is shown to be in good agreement with the experimental measurements over a wide range of air masses and average clearness indices.