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

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)