Clouds and Trophospheric Aerosols from Satellites

Abstract

Interactions of clouds and aerosols with incoming solar and outgoing terrestrial radiation partly determine the Earth’s energy balance and climate. Both clouds and tropospheric aerosols are definable as suspensions of particles in the atmosphere. The principal difference between them is the size of the particles. Aerosol particles typically range from 0.001 µm to 1 µm in radius, cloud particles from 1 µm to 100 µm. The larger sized cloud particles cause about 100 times greater absorption or scattering of radiation than do the aerosol particles. This explains, for example, why visibility is lower in fog (cloud) than in haze (aerosol). Aerosols show more of a decrease in absorption and scattering with increased wavelength than do clouds. Thus, clouds generally interact about equally with incoming solar radiation and emitted thermal radiation, whereas aerosols interact mainly in the shortwave (solar) portion of the spectrum. The actual effect of clouds and aerosols on the Earth’s radiation balance and climate also depends on many other factors, such as chemical composition and concentrations, both vertically and horizontally.