Ground-based observations of O2+ 1N Band enhancements relative to N2+ 1N band emission

Abstract

Spectrometric measurements in normal aurora of O2+ first negative (1N) and N2+ first negative (1N) emissions over the wavelength range 5175-5325 A have been obtained with coincident incoherent scatter radar measurements with both instruments pointed in the same direction, the geomagnetic zenith. A comparison of the inferred mean energies derived from the radar observations for several normal aurora was made with the spectral ratio I(O2+ 1N; 2, 0)/I(N2+ 1N; 0, 3) obtained from the optical observations. The intensity ratio was found to decrease by nearly 40% from aurora with mean energy ~ 10 keV to aurora with mean energy ~ 2 keV. The altitude of the peak E-region electron density co-varied with the spectral ratio from ~ 105 km for the harder aurora to ~ 130 km for the softer aurora. The inferred rotational temperature from the matching synthetic spectra co-varied from 250 to 500 K over the same energy limits. Model analysis based on both mono-energetic and Maxwellian precipitating electron fluxes show reasonable agreement with the observed I(O2+ 1N; 2, 0)/I(N2+ 1N; 0, 3) ratio when MSIS n(O2) and n(N2) densities corresponding to the experimental dates are used.