O + , O, and O 2 densities derived from measurements made by the High Resolution Airglow/Aurora Spectrograph (HIRAAS) sounding rocket experiment

We present the results of an analysis of the O II 834 Å and O I 1356 Å altitude profiles measured during a sounding rocket flight on March 19, 1992. The profiles were analyzed using a new set of models that used discrete inverse theory to seek a maximum likelihood fit to the data. Both profiles were fit simultaneously to ensure consistency of the retrieved ionosphere and thermospheric neutral density. During the analysis the thermospheric neutral density and temperature were modeled using the Mass Spectrometer Incoherent Scatter (MSIS‐86) model [ Hedin , 1987]. Two parameters were used to scale the absolute MSIS O and O 2 densities; the exospheric temperature was altered by varying the 10.7 cm solar flux (an MSIS‐86 input). The ionospheric O + density was modeled by a three‐parameter Chapman layer. The retrieved MSIS scalars for the O and O 2 densities were 0.47 ± 0.09 and 0.58 ± 0.14, respectively. These scalars indicate that the MSIS‐86 model predicted significantly higher O and O 2 densities. The inferred exospheric temperature was 1125 K in good agreement with the MSIS‐86 prediction. The derived O density is in good agreement with the O density inferred from midultraviolet spectra observed during the same rocket flight [ Bucsela et al. , 1998]. The retrieved F region peak density, 1.98 ± 0.63 × 10 6 cm −3 , peak height, 291 ± 22 km, and plasma scale height, 138 ± 24 km, all agreed with coincident digisonde measurements. Thus we have demonstrated that the ionospheric state can be accurately determined by inversion of observed O II 834 Å limb radiance profiles.