The altitude dependence of the OH(X 2Π) vibrational distribution in the nightglow: Some model expectations

Abstract

A number of different OH Meinel band excitation models are used to investigate the extent to which quenching and vibrational deactivation processes could cause the nightglow OH vibrational distributions to vary with altitude. The various models, which are based upon those described by McDade and Llewellyn (1988, Planet. Space Sci. 36, 897), are used to calculate the steady state OH vibrational distributions throughout the 80–100 km region. The results of the calculation show that, irrespective of the basic model assumptions, the OH vibrational distributions should not be strongly altitude dependent and that the emission profiles of the Meinel bands from the υ′ levels 1 through 9 should not differ in altitude by more than one or two kilometers. The results of some recent laboratory studies pertaining to the Meinel band excitation mechanism are also discussed and it is shown that stepwise collisional vibrational deactivation is unlikely to play a major role in controlling the observed nightglow OH vibrational distribution.