Shortwave radiation climatonomy

Abstract

Functional relations are discussed which express absorbing and scattering processes of shortwave radiation in the atmosphere. A simplified model is derived in which only overall intensities (integrated over the spectral band of insolation) are considered. Balance requirements are established which relate “top albedo” to effective absorption in the air and by the ground, both as fractions of extra-atmospheric irradiance. Measurements of diffuse radiation from the sky, in addition to global radiation, are used to specify scattering versus absorption components of aerosol attenuation for clear-sky conditions with known liquid water content and Rayleigh scattering. Data from three continental locations are selected which are representative of clear-sky attenuation over a desert (La Joya, Peru), an open prairie (O'Neill, Nebraska), and an industrialized urban area (Kew, England). The ratio of absorption to scattering shows significant systematic variation, city aerosol being more efficient as absorber, desert aerosol more as a scatterer. Effects are calculated which result from a systematic variation of (1) surface albedo, (2) liquid water content, (3) aerosol, and (4) cloud cover. Among other results it is demonstrated how top albedo (measurable nowadays from orbiting or synchronous satellites) will react to changes in surface albedo and aerosol scattering. It is also shown numerically, how cloud effects on global radiation are modified by the existing turbidity conditions in the cloudless air.