The Filling-In of Fraunhofer Lines in the Day Sky

Ground-based high resolution (R ≈ 120,000) spectra of the zenith day sky near 6300 Å were obtained with a PEPSIOS. When compared with the solar spectrum taken with the same spectrometer the filling-in of Fraunhofer lines (the Ring effect) in the day sky was clearly present. The observed effect was in the range 0.2 to 2.0% of the continuum. This corresponds to an apparent intensity of 0.5 to 3.0 × 1010 photons s−1 Å−1 cm−2. The observed behavior of the effect with solar zenith angle is consistent with the source being primarily the fluorescence of aerosol.