Ground-based observations of O 2 ( b1Σ+g− X3Σ−g) atmospheric bands in high latitude auroras

Abstract

Analysis of observed spectrograms is based on comparison with synthetic spectra. The O 2( b 1 Σ + g − X 3 Σ − g Atm. (1,1) band in high latitude auroras observed from the ground is found to be the strongest in the Δv = 0 sequence. It is enhanced with altitude relative to the N 2 1P(2, 0)and N + 2 M(2,0) bands, but the O 2 Atm. (2, 2) band has an unexpected low intensity. The range of rotational temperatures of the O 2 Atm. bands varies from approx. 200 to above 500 K which indicates that the altitude of the centroid of the emission region varies from about 100 km to the F-region. The highest temperature is found in the midday aurora associated with the magnetospheric cusp. Conspicuous relative variations between the intensities of N 2 and O 2 spectra are documented, but a satisfactory explanation of the variety is not given. Deviations of the observed O 2 Atm. band intensities from the vibrational intensity distribution predicted by Franck-Condor factors indicate that the excitation of the O 2 Atm. bands in aurora is not mainly due to particle impact on O 2, and the contribution due to energy transfer from hot O( 1D) atoms has to be found in future research.