Thermospheric Composition Changes in the Morning Sector near Local Midnight in Association with Substorm Activity and IMF Orientation
Abstract
Repeated observations with DE-1 and other spacecraft have established that transient decreases in the far-ultraviolet (FUV) terrestrial OI emissions at subauroral latitudes in the morning sector are associated with decreases in the O/N2 ratio at thermospheric altitudes. These decreases are observed following onset of intense auroral activity and, at northern latitudes near the autumnal equinox, the greater spatial extent and depth of decrease are associated with a positive IMF By component. These changes in thermospheric composition directly affect F-region electron densities. It is believed that the altered composition is driven by aurorally related heating and the antisunward polar jet, which transports heated air to subauroral latitudes in the very early hours of local time and then into the morning sector. FUV observations of this altered composition close to local midnight and in the early morning hours are lacking, due in part to the need for FUV observations in the sunlit hemisphere (i.e., local summer), but are necessary to support this general expectation. Other important influences are also present. The GUVI/TIMED observations at FUV wavelengths are providing an extensive new set of unambiguous thermospheric composition measurements over a wide range of local times and latitudes in both auroral hemispheres as the orbit of the near-polar-orbiting TIMED spacecraft processes rapidly in local time. These data are being scanned in a search for the requisite combination of sampling at the right local times and season in periods of auroral substorms to provide answers to the question of composition changes near local midnight and the early morning hours. A further report on this search and its findings are presented in this paper.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFMSA34A..08C
- Keywords:
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- 2435 Ionospheric disturbances;
- 0310 Airglow and aurora;
- 0355 Thermosphere: composition and chemistry;
- 0358 Thermosphere: energy deposition