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Rotational Raman scattering and the ring effect in zenith‐sky spectra
Author(s) -
Fish D. J.,
Jones R. L.
Publication year - 1995
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/95gl00392
Subject(s) - zenith , sky , solar zenith angle , optics , raman spectroscopy , diffuse sky radiation , spectrometer , spectral line , scattering , atmosphere (unit) , spectroscopy , physics , computational physics , materials science , astrophysics , astronomy , meteorology
The technique of zenith‐sky spectroscopy is widely used to measure the vertical columns of O 3 , NO 2 , OClO and BrO in the atmosphere. In this paper, a model to simulate the effect of rotational Raman scattering by O 2 and N 2 on zenith‐sky spectra is presented. The model is used to calculate the Raman‐scattering cross‐section for zenith‐sky measurements and this cross‐section is shown to correspond closely to the measured Ring cross‐section, supporting the case that Raman scattering is the major cause of the Ring effect. Raman scattering is also shown to reduce the depths of structured molecular absorptions in scattered light spectra, leading to a general underestimation of the slant columns of molecules measured by zenith‐sky spectroscopy which can be significant in some cases. This effect varies with solar zenith angle, so will affect particularly attempts to retrieve the vertical profile of an absorber from the variation of slant column with zenith angle. The calculated Ring cross‐section is used to infer the proportion of multiply‐scattered light which enters a zenith‐sky spectrometer at twilight, and thus to estimate the magnitude of the corresponding underestimation of measured slant columns.