ABSORPTION OF SOLAR-RADIATION BY ATMOSPHERIC O-4

Spectroscopic measurements of the atmospheric solar radiation attenuat ion reveal that the near ultraviolet-visible-near-infrared absorption of the oxygen collision complex (O-2)(2), thus far omitted from models , is important for the direct heating for both clear and cloudy skies. Atmospheric line-by-line radiative transfer calculations show that th e absorption by (O-2)(2) leads to a globally averaged clear sky shortw ave (SW) heating of about 0.53 W m(-2). It is therefore proposed that the absorption by (O-2)(2) should be included in models designed to ca lculate the SW heating. It is shown that due to its weak absorption un der clear sky, the SW heating by (O-2)(2) approximately increases line arly with increasing optical pathlengths for cloudy sky conditions. Th is is in contrast to SW heating by the molecular absorptions of H2O or O-2, whose absorption lines are already partially saturated under cle ar sky, causing the SW heating (due to these gases) to increase rather as the square root of the optical path. From a limited number of clou dy sky optical path observations, the atmospheric (O-2)(2) absorption is estimated to account for an additional solar heating of about 0.57 W m(-2) globally averaged.