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Ann. Geophys., 16, 711-720, 1998
www.ann-geophys.net/16/711/1998/
© European Geosciences Union 1998
Non-trough foF2 enhancements at near-equatorial dip latitudes
E. Sambou1, P. M. Vila2, and A. T. Kobea3
1Département de Physique, Université C. Anta Diop, Dakar-Fann, Senegal
2Centre d'Étude des Environnements Terrestres et Planétaires (CETP), 4 Avenue de Neptune, F-94107, Saint-Maur-des-Fossés, France
3Département de Physique de l'Atmosphère, Université de Cocody, 22 BP582, Abidjan 22, Côte d'Ivoire
Abstract. Fine resolution series from three equatorial
ionosondes of the IEEY network in West Africa have revealed small-scale daytime
peak F2 structures, superposed on the slowly varying minimum or
"trough" distribution in the ±5° magnetic latitude zone. We report
this new morphology, concentrating on foF2 enhancements of two types:
near-equatorial crests (which travel either northwards or southwards) and
magnetic field-aligned domes, whose onsets last only tens of minutes. Both types
are observed to start at mid-morning or early afternoon hours. We relate their
occurrence with the available variations of Vz=E × B
upward drift which feeds the equatorial plasma fountain. We suggest the foF2
enhancements to be triggered by brief slow-downs of the Vz velocity near
F2 peak altitude in our West African sector. Their short latitude extent
differentiates them from the larger-scale tropical crest system. Further
analysis of these features should lead to weather-like models of the low
latitude ionosphere variations, where unstable local coupling between processes
seems to be the trigger.
Key words. Ionosphere (Equatorial ionosphere ·
Ionosphere-atmosphere interaction · Plasma temperature and density)
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