11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Wednesday, 5 June 2002
The Ring effect in the presence of aerosols/thin clouds
David E. Flittner, Univ. of Arizona, Tucson, AZ; and J. Joiner
The filling in of solar Fraunhofer lines, also known as the Ring effect, has been observed in both ground-based and satellite-based observations. Several studies have concluded that Rotational Raman scattering is the cause. While the Ring effect introduces spectral structure that must be removed when performing retrievals of atmospheric constituents, its mere presence says something about the amount of molecular scattering. This has allowed cloud top/terrain pressure to be estimated using measurements of satellite backscatter UV measurements.

To investigate the effect aerosols may have upon the Ring effect, a radiative transfer model with inelastic scattering has been created for a plane parallel atmosphere. For simplicity, the method of successive orders of scattering is used in the model. Sensitivity of the Ring effect, at a wavelength near 393 nm, to single-layer aerosol clouds with optical depths less than or equal to one are shown for different cloud top pressures and surface albedos. Dependence upon aerosol single scatter albedo and forward scattering asymmetry parameter is also explored. In general, when the aerosol optical depth of non-absorbing particles is increased, the Ring effect is decreased over low albedo surfaces and increased over high albedo surfaces. Decreasing the cloud top pressure increases the influence of the aerosols. Absorbing aerosols reduce both the backscattered radiance and the Ring effect. The possibility of identifying thin cirrus clouds over ice or the height of UV absorbing aerosol layers is examined.

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