Observations of middle ultraviolet emissions in the middle and lower thermosphere:: NO, O2, O, and Mg+

We present an analysis of day and night limb spectra obtained from the Ionospheric Spectroscopy and Atmospheric Chemistry ( ISAAC) satellite instrument in the middle ultraviolet spectral region between 260 and 300 nm. Tangent heights above the Earth's surface range from 81 to 200 km. These spectra contain signatures of daytime fluorescent scattering by nitric oxide in the g bands, emission by atomic oxygen at 297.2 nm, and fluorescent scattering by ionized magnesium. The night spectra are dominated by the Herzberg bands of molecular oxygen. Our analysis includes retrievals for vertical profile densities of NO and slant column densities of O and Mg+ in the lower thermosphere. We show how these quantities are related to variable inputs of solar soft X-ray and extreme ultraviolet radiation. The Herzberg band emission is used to constrain the ratio of Herzberg I to Herzberg II band emission and to determine the nighttime vibrational distribution of the excited A(3)Sigma(+)(u) state of molecular oxygen.