Quantitative spectroscopy of the aurora. IV. The spectrum of medium intensity aurora between 8800 Å and 11 400 Å

Abstract

An averaged spectrum of medium intensity aurora (I(4278 Å) ≈ 20 kR) at a resolution of 15 Å from 8800 Å to 11 400 Å is presented. The observations were made with a grating spectrometer and S1 photomultiplier detector. Synthetic comparison spectra were prepared to aid in the identification and relative intensity measurements of the observed emission features. Included in the synthesis were the nitrogen first positive, Meinel, and infrared afterglow systems, the oxygen atmospheric system, the hydroxyl vibration–rotation system, and a number of atomic emissions. Three unidentified features have been tentatively ascribed to NI multiplets. Comparisons have been made between the observed and theoretically calculated relative populations of the four lowest vibrational levels in the upper electronic states of both the nitrogen first positive and Meinel systems. The relative vibrational populations of N2(B3Π) do not fit the hypothesis of direct electron impact excitation plus cascade through the N2 second positive system. The relative vibrational population rates of the Meinel N2+ system deviate from the Franck–Condon factors for the excitation transition.