High rotational excitation of NO infrared thermospheric airglow: A signature of superthermal nitrogen atoms?

The reaction between superthermal N([SUP]4[/SUP]S) atoms produced by exothermic processes and O[SUB]2[/SUB] has been proposed to explain observations of highly rotationally excited nitric oxide in the sunlit thermosphere. We examine the importance of this mechanism using a detailed calculation of the fast N([SUP]4[/SUP]S) atoms energy distribution. It is shown that the hot thermal N atoms are able to produce rotationally excited NO in the upper thermosphere through the reaction of O[SUB]2[/SUB] with N([SUP]4[/SUP]S). By contrast, near the NO peak at 110 km, the Maxwellian nitrogen atoms produce substantially less rovibrationally excited NO than the superthermal component. Consequently, the non Maxwellian N([SUP]4[/SUP]S) atoms show a clear spectral signature in the (1-0) and (2-1) bandheads at this altitude. The calculated rovibrationally excited NO concentration at 140 km is shown to be consistent with the value derived from the analysis of infrared airglow spectra