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Journal of Geophysical Research

Far ultraviolet atomic and molecular nitrogen emissions in the dayglow


  • P. Z. Takacs,

  • P. D. Feldman


The far ultraviolet day airglow between 1130 and 1520 Å was observed at 4.4-Å spectral resolution with a scanning spectrophotometer aboard an Aerobee rocket on December 11, 1972. Fourteen bands, or blends, of the N2 Lyman-Birge-Hopfield (LBH) system are clearly resolved and indicate a total LBH system zenith column emission rate of 3810 ± 520 R extrapolated to the subsolar point. No LBH bands originating from vibrational levels with υ′ > 6 are observed, nor are any bands of the N2 Birge-Hopfield system observed. A photoelectron flux model, based on recent photoelectron flux measurements and the observed LBH altitude profile, is used to calculate the direct and dissociative excitation contributions to the atomic nitrogen emissions. An atomic nitrogen density of the order of 4 × 107 cm−3 at 190 km is required to account for the observed 77 ± 8 R N I λ 1493 intensity and the 580-R N I λ 1200 intensity, both of which are produced primarily by direct electron impact excitation of atomic nitrogen. This density is in agreement with other recent measurements but is an order of magnitude greater than earlier photochemical model results.

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