Downward flux of atmospheric 63-μm emission from atomic oxygen at balloon altitudes

The 63- mu m emission line from the ground electronic state finestructure transition (P sub(1) -3-P sub(2) -3) of atomic oxygen (suggested as a major source of thermospheric cooling by Bates and, subsequently, discussed theoretically) has been measured over a range of thermospheric altitudes. The rocket measurements show that the downward intensity remained essentially constant between 85 and 100 km, as expected for an optically thick emitting region. As a result, O I emission is considered to be less important as a source of atmospheric cooling than upward radiation from the 5.3- mu m band of NO. Nevertheless, measurements of the intensity distribution of O I emission in the lower thermosphere should help to discriminate between theoretical models and, in particular, address the appropriateness of local thermodynamic equilibrium at these altitudes. The authors report high spectral resolution measurements of O I emission at 30 km. The downward O I flux is measured to be (2.4 plus or minus 0.5) x 10 super(-) super(5) W m super(-) super(2) sr super(-) super(1) , somewhat larger than expected on the basis of previous rocket measurements or theoretical predictions. This value is independent of zenith angle.