SPECTRAL BAND RESOLUTION OF SOLAR-RADIATION IN ATHENS, GREECE

A 14-year (1977-1990) record of global solar radiation measurements pe rformed in Athens, Greece, has been utilized to determine the distribu tion of radiant energy in the various wavelength bands. The monthly me an values of the irradiation ratios in the spectral intervals, blue (0 .380-0.525 mum), green-orange (0.525-0.630 mum), red (0.630-0.710 mum) , and photosynthetically active radiation (PAR) (0.380-0.710 mum) and the global irradiation (0.3-2.8 mum) compare favourably with values re ported in the literature for different locations over a wide geographi cal area. The irradiation ratios exhibit seasonal variations attributa ble to changes in local air-mass climatology. It is observed that the proportion of the radiant energy in the various spectral bands relativ e to the global solar irradiation increases as sky conditions change f rom 'clear' to 'partly cloudy'. Finally, the observed seasonal depende nce of the broad-band spectral energy distribution is essentially caus ed by changes in the composition of the air masses (turbidity, airborn e pollutants, clouds) in residence at the measurement site in the cour se of the year.