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Published January 20, 1992 | Published
Journal Article Open

Enhancement of Atmospheric Radiation by an Aerosol Layer

Abstract

The presence of a stratospheric haze layer may produce increases in both the actinic flux and the irradiance below this layer. Such haze layers result from the injection of aerosol-forming material into the stratosphere by volcanic eruptions. Simple heuristic arguments show that the increase in flux below the haze layer, relative to a clear sky case, is a consequence of "photon trapping." We explore the magnitude of these flux perturbations, as a function of aerosol properties and illumination conditions, with a new radiative transfer model that can accurately compute fluxes in an inhomogeneous atmosphere with nonconservative scatterers having arbitrary phase function. One calculated consequence of the El Chichon volcanic eruption is an increase in the midday surface actinic flux at 20°N latitude, summer, by as much as 45% at 2900 Å. This increase in flux in the UV-B wavelength range was caused entirely by aerosol scattering, without any reduction in the overhead ozone column.

Additional Information

© 1992 by the American Geophysical Union. Received November 28, 1989; revised May 8, 1991; accepted may 8, 1991. Paper number 91JD01308. We thank J. Pollack and the anonymous referees for their extremely helpful comments. This research is supported by EPA grant 9D4125NALX to the California Institute of Technology. Contribution number 4685 from the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena California 91125.

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