On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering

The "filling-in" (FI) of Fraunhofer lines, often referred to as the Ring effect, was examined using measurements of near ultraviolet sunlight scattered from the zenith sky above Boulder, Colorado during July and August 2005. The FI of the 344.1 nm Fe I line was directly determined...

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Main Authors: A. O. Langford, R. Schofield, J. S. Daniel, R. W. Portmann, M. L. Melamed, H. L. Miller, E. G. Dutton, S. Solomon
Format: Article
Language:English
Published: Copernicus Publications 2007-01-01
Series:Atmospheric Chemistry and Physics
Online Access:http://www.atmos-chem-phys.net/7/575/2007/acp-7-575-2007.pdf
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spelling doaj-a5d56cdc7108479ba8298d38b4b3eae02020-11-24T23:27:11ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242007-01-0173575586On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scatteringA. O. LangfordR. SchofieldR. SchofieldR. SchofieldJ. S. DanielR. W. PortmannM. L. MelamedM. L. MelamedH. L. MillerH. L. MillerE. G. DuttonS. SolomonThe "filling-in" (FI) of Fraunhofer lines, often referred to as the Ring effect, was examined using measurements of near ultraviolet sunlight scattered from the zenith sky above Boulder, Colorado during July and August 2005. The FI of the 344.1 nm Fe I line was directly determined by comparing direct sun and cloud-free zenith sky spectra recorded on the same day. The results, obtained over solar zenith angles (SZA) from 20° to 70°, are compared to the predictions of a simple rotational Raman Scattering (RRS) spectral model. The measured FI was found to be up to 70% greater than that predicted by first-order molecular scattering with a much stronger SZA dependence. Simultaneously measured aerosol optical depths and Monte Carlo calculations show that the combination of aerosol scattering and second-order molecular scattering can account for these differences, and potentially explain the contradictory SZA dependences in previously published measurements of FI. These two scattering processes also introduce a wavelength dependence to FI that complicates the fitting of diffuse sunlight observations in differential optical absorption spectroscopy (DOAS). A simple correction to improve DOAS retrievals by removing this wavelength dependence is described.http://www.atmos-chem-phys.net/7/575/2007/acp-7-575-2007.pdf
collection DOAJ
language English
format Article
sources DOAJ
author A. O. Langford
R. Schofield
R. Schofield
R. Schofield
J. S. Daniel
R. W. Portmann
M. L. Melamed
M. L. Melamed
H. L. Miller
H. L. Miller
E. G. Dutton
S. Solomon
spellingShingle A. O. Langford
R. Schofield
R. Schofield
R. Schofield
J. S. Daniel
R. W. Portmann
M. L. Melamed
M. L. Melamed
H. L. Miller
H. L. Miller
E. G. Dutton
S. Solomon
On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
Atmospheric Chemistry and Physics
author_facet A. O. Langford
R. Schofield
R. Schofield
R. Schofield
J. S. Daniel
R. W. Portmann
M. L. Melamed
M. L. Melamed
H. L. Miller
H. L. Miller
E. G. Dutton
S. Solomon
author_sort A. O. Langford
title On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
title_short On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
title_full On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
title_fullStr On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
title_full_unstemmed On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
title_sort on the variability of the ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering
publisher Copernicus Publications
series Atmospheric Chemistry and Physics
issn 1680-7316
1680-7324
publishDate 2007-01-01
description The "filling-in" (FI) of Fraunhofer lines, often referred to as the Ring effect, was examined using measurements of near ultraviolet sunlight scattered from the zenith sky above Boulder, Colorado during July and August 2005. The FI of the 344.1 nm Fe I line was directly determined by comparing direct sun and cloud-free zenith sky spectra recorded on the same day. The results, obtained over solar zenith angles (SZA) from 20° to 70°, are compared to the predictions of a simple rotational Raman Scattering (RRS) spectral model. The measured FI was found to be up to 70% greater than that predicted by first-order molecular scattering with a much stronger SZA dependence. Simultaneously measured aerosol optical depths and Monte Carlo calculations show that the combination of aerosol scattering and second-order molecular scattering can account for these differences, and potentially explain the contradictory SZA dependences in previously published measurements of FI. These two scattering processes also introduce a wavelength dependence to FI that complicates the fitting of diffuse sunlight observations in differential optical absorption spectroscopy (DOAS). A simple correction to improve DOAS retrievals by removing this wavelength dependence is described.
url http://www.atmos-chem-phys.net/7/575/2007/acp-7-575-2007.pdf
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