Oxygen recombination in the tropical nightglow

Abstract

In order to explain O I lines in the tropical nightglow, complete and reasonably accurate recombination and emission rate coefficients are used to construct a detailed radiative cascade model of a recombining oxygen plasma. Effective recombination coefficients are given for all low quantum number O I levels for the two limiting cases of zero and infinite optical depth of the resonance lines. The direct recombination coefficients for the S levels, and to a lesser extent the P levels, are significantly smaller than those previously quoted in the literature. The quantitative evaluation of radiative cascading in the optically thin limit predicts an order of magnitude lower intensity for the 1304-Å line than that predicted by a recently published optically thin model using an estimate of the cascade contributions to the intensity. However, the optically thick model, which is more realistic for the F2 region than the thin model, predicts a 1304-Å intensity in good agreement with observations of the 1304-Å line.