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Ann. Geophys., 22, 3099-3107, 2004
www.ann-geophys.net/22/3099/2004/
© European Geosciences Union 2004
Global observations of the zonal drift speed of equatorial ionospheric plasma bubbles
T. J. Immel1, H. U. Frey1, S. B. Mende1, and E. Sagawa2
1Space Sciences Laboratory, University of California Berkeley, USA
2Communications Research Laboratory, Tokyo, Japan
Abstract. Space-based measurements from an imager aboard the high-apogee NASA-IMAGE satellite
allows for global-scale observations of nightside ionospheric densities and structure.
Such a view cannot be provided by imagers in near-Earth orbit or based on the ground.
The IMAGE Spectroscopic Imager (SI) isolates the Far-ultraviolet (FUV) O I 135.6nm
emission which is produced through radiative recombination of O+. These observations
clearly show the distribution of FUV emissions of the equatorial airglow bands over the
range of local times between the evening terminator to points well after midnight. Determination
of plasma drift speeds in these local time sectors is performed by identification and subsequent
tracking of localized depressions in the FUV emissions. This determination is made for nearly 200
plasma bubbles in the March-May period of 2002. Important findings of this study include (1) an
unambiguous association between Dst and zonal plasma drift speeds, and (2) a longitudinal
dependence of the zonal plasma drift speeds, with a peak around the Indian sector. The first
effect is attributed to penetrating ring current electric fields, while the second is apparently
due to a longitudinal variability in the vertical polarization electric fields that directly
affects the zonal plasma drift speeds.
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