NON-TROUGH FOF2 ENHANCEMENTS AT NEAR-EQUATORIAL DIP LATITUDES

Fine resolution series from three equatorial ionosondes of the IEEY ne twork in West Africa have revealed small-scale daytime peak F2 structu res, superposed on the slowly varying minimum or ''trough'' distributi on in the +/-15 degrees magnetic latitude zone. We report this new mor phology, concentrating on foF2 enhancements of two types: near-equator ial crests (which travel either northwards or southwards) and magnetic field-aligned domes, whose onsets last only tens of minutes. Both typ es are observed to start at midmorning or early afternoon hours. We re late their occurrence with the available variations of Vz = E x B upwa rd drift which feeds the equatorial plasma fountain. We suggest the fo F2 enhancements to be triggered by brief slow-downs of the Vzvelocity near F2 peak altitude in our West African sector. Their short latitude extent differentiates them from the larger-scale tropical crest syste m. Further analysis of these features should lead to weather-like mode ls of the low latitude ionosphere variations, where unstable local cou pling between processes seems to be the trigger.