Data Analysis - Ground-Based

Ground-based observations of the aurora for key emission features (the atomic oxygen (O) features OI 844.6 nm and OI 630.0 nm and the molecular nitrogen features N₂ 1NG 427.8 nm and N₂ 1PG 871.0 Nm) can be used to infer characteristics of the precipitating electrons producing the aurora (average energy <E> and energy flux Q) and the abundance of O relative to N₂ (O/N₂). The latter quantity is of particular interest since it frequently decreases during active aurora as a result of heating (Joule and particle) within the auroral oval. CPI, in collaboration with scientists from the Aerospace Corporation, has developed algorithms for inferring <E>, Q, and O/N₂ from ground-based observations of the above features and others [Strickland et al., J. Geophys. Res., 94, 13527, 1989 and Hecht et al., J. Geophys. Res., 104, 33, 1999]. A number of papers have been published using the algorithms on Aerospace ground-based auroral data. The key results appearing in these papers are temporal variations in O/N₂ (what is actually published is a scaling factor for the O density referenced to quite-time conditions) from nighttime observing periods that extend over several hours. This type of information is of considerable interest to the local dynamics of the thermosphere within and near heated regions. Examples of papers are the above Hecht et al. paper, Hecht et al. [J. Geophys. Res., 100, 17,285, 1995] and Hecht et al. [J. Geophys. Res., 96, 5757, 1991]. Independent verification of the composition results has come from analyses of coincident auroral rocket data [Strickland et al., J. Geophys. Res., 102, 2475, 1997 and Strickland et al., J. Geophys. Res., 105, 2461, 2000].