Abstract
Ultraviolet dayglow observed using the Ionospheric Spectroscopy and Atmospheric Chemistry (ISAAC) satellite instrument is used to determine the concentration of nitric oxide (NO) in the upper mesosphere and thermosphere. ISAAC was launched in February 1999 on board the Advanced Research and Global Observing Satellite (ARGOS). We focus on ISAAC dayside limb observations at tangent altitudes between 80 and 200 km and over the latitude range 40°N–70°S. The data analyzed here were obtained in November and December 1999 during a period of moderate to high solar activity. The NO density retrievals include constraints on instrument sensitivity, in‐flight assessments of stray light, and determinations of Rayleigh‐scattered background contributions. Residual spectra contain strong dayglow signatures of the NO γ bands which are used for inversion of measured radiances to absolute NO concentrations. Comparison between ISAAC measurements and photochemical calculations indicates improved agreement above 130 km using O2 and temperatures from the new NRLMSISE‐00, as compared to the MS model. In the lower thermosphere, observed daily variations in low‐latitude nitric oxide are strongly correlated with variations in the solar soft X‐ray flux.
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