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 Angstrom and O I 1356 Angstrom altitude profiles measured during a sounding rocket flight on Mar ch 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 io nosphere and thermospheric neutral density. During the analysis the thermos pheric neutral density and temperature were modeled using the Mass Spectrom eter Incoherent Scatter (MSIS-86) model [Hedin, 1987]. Two parameters were used to scale the absolute MSIS O and O-2 densities; the exospheric tempera ture 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 p redicted significantly higher O and O-2 densities. The inferred exospheric temperature was 1125 K in good agreement with the MSIS-86 prediction. The d erived O density is in good agreement with the O density inferred from midu ltraviolet spectra observed during the same rocket flight [Bucsela et al., 1998]. The retrieved F region peak density, 1.98 +/- 0.63 x 10(6) cm(-3), p eak height, 291 +/- 22 km, and plasma scale height, 138 +/- 24 km, all agre ed with coincident digisonde measurements. Thus we have demonstrated that t he ionospheric state can be accurately determined by inversion of observed O II 834 Angstrom limb radiance profiles.