Non-trough <i>fo</i>F2 enhancements at near-equatorial dip latitudes

Abstract

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 ®eld-aligned domes, whose onsets last only tens of minutes. Both types are observed to start at midmorning 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 dierentiates 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 á Ionosphere-atmosphere interaction á Plasma temperature and density)

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“…5. Evolution of the f 0 F 2 (bottom panels) and H component of the Earth's magnetic field (top panels), D is for Dakar, O for Ouagadougou and K for Korhogo (from Sambou et al, 1998). cycle years (Faynot and Vila, 1979). These discrepancies are not yet understood.…”