The available hourly values of solar radiant components are grouped into daily, seasonal and annual data sets. Fig. 1 shows the seasonal trends of daily radiant fluxes, RS versus QP (Fig. 1a), and Rd versus QPd (Fig. 1b), respectively, for the period of measurements. It is clear that both spectral PAR components, QP and QPd, are highly correlated with broadband RS and Rd irradiances suggesting further that daily spectral values can be obtained directly from broadband values. The seasonal trend in daily QP closely follows the trend in RS, with lowest and highest values occurring during
cool and warm season, respectively. Large variability in both radiant fluxes QP and RS occurs during winter and spring, whereas weak variability occurs during summer and autumn. In contrast, the seasonal trends in both daily QPd and Rd fluxes (Fig. 1b) do have much greater variability than global solar components at the same time. Overall, QPd and Rd fluxes attain similar seasonal trends, with a large day-to-day variability mainly due to cloudiness.