Tidal and Ionospheric Contributions in GUVI O/N2 wave-4 Signals and Implications for F-region Plasma Density Variability
Abstract
The longitude/local time modulation of the column number density ratio of atomic oxygen to molecular nitrogen (O/N2 ratio) observed by GUVI/TIMED shows several features that are inconsistent with the known tidal structures in the thermosphere. The zonal wavenumber 4 (wave-4) pattern that is usually associated with the eastward propagating DE3 and SE2 nonmigrating tides is propagating westward and the diagnosed relative O/N2 amplitudes of 5-10% are larger than expected from a thermosphere-tidal coupling perspective. Two recent studies from the GUVI team already established the leading source of the bogus wave-4 tidal signals: ionospheric contamination of the O/N2 ratio derived from GUVI's optical observations caused by radiative O+ recombination in the F-region. However, the apparent westward propagation in the wave-4 GUVI O/N2 ratio remained unexplained since the ionospheric contamination pattern itself is controlled by the DE3 and SE2 tides in the F-region plasma and should thus propagate eastward. This paper revisits the problem by separating the "true" thermospheric tidal signal in the GUVI O/N2 ratio from the ionospheric contamination using the TIMED-based empirical climatological tidal model of the thermosphere (CTMT) and supporting COSMIC TEC tidal diagnostics. As such, it provides new observational information about the impact of tidally-induced composition changes on ionospheric variability. Furthermore, it is shown that the superposition of DE3, SE2, and SPW4 from ionospheric and thermospheric sources produces the apparent westward propagation in O/N2, which will be helpful to interpret the forthcoming GOLD and ICON observations.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMSA14A..06O
- Keywords:
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- 0355 Thermosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 2437 Ionospheric dynamics;
- IONOSPHERE;
- 2494 Instruments and techniques;
- IONOSPHERE;
- 2794 Instruments and techniques;
- MAGNETOSPHERIC PHYSICS