On the Transfer of Solar Radiation in Aerosol Atmospheres

Abstract

A radiation scheme has been developed by which the absorption of water vapor in the near-infrared regions of the solar spectrum can be inserted into the transfer program for inhomogeneous aerosol atmospheres. The incorporation of water vapor absorption in a scattering atmosphere is accomplished by a series of exponential fits to the band absorptivity based upon laboratory measurements. Band-by-band calculations have been carried out for the heating rate, local albedo, total absorption, and diffuse transmission in model hazy and clear atmospheres. In a hazy atmosphere, the solar heating rates may be as much as 5 and 9°C day?1 for surface albedos of 0.1 and 0.8, respectively. Local-albedo calculations for the entire solar spectrum reveal that a surface albedo of about 0.3?0.4 plays a significant role on the increase or reduction of a globally averaged albedo caused by the increase of aerosol concentrations in the atmospheric boundary layer. An increase of aerosol loading leads to an increase of the total absorption within the atmosphere, whereas it reduces the solar flux available to the earth's surface for absorption. Consequently, in a hazy atmosphere cooling takes place near the surface with warming aloft. The net heating effect for the earth-atmosphere system, however, depends strongly upon the surface characteristics.