Polar cap optical observations of topside (>900 km) molecular nitrogen ions

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Abstract
The Ballistic Missile Defense Organization's (BMDO) Midcourse Space Experiment (MSX) has obtained the first optical observations of molecular ions at very high altitudes above the northern polar cap. Spectra over geomagnetic latitudes ∼ 80°N, at 1300 MLT of the N2+ 1st Negative Bands are identified with a total band intensity of 2.5 kR and an implied number density of 10³ ions cm−3 at 900 km. Additional N2+ transitions from the Meinel bands were also observed. No other permitted optical emissions were observed above 450 km indicating that the source must be solar resonance fluorescence of the N2+ ion. The presence of heavy molecular ions at high altitudes is an indication of the upward flow of ions from the ionosphere into the magnetosphere. These optical observations suggest a new technique for the study of the global structure and temporal variation of plasma energization and transport between the ionosphere and magnetosphere in the polar regions.

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