Nighttime medium-scale traveling ionospheric disturbances at low geomagnetic latitudes

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) are a commonly-observed structure in the middle latitude ionosphere during the months surrounding the solstices and low solar flux conditions. MSTIDs consist of one or more narrow bands exhibiting uplift in F-region electron density which are elongated from northwest to southeast in the northern hemisphere and southwest to northeast in the southern hemisphere. These electrified structures propagate westward and toward the equator in a direction perpendicular to their long dimension. Previously, this type of MSTID was not thought to occur at magnetic latitudes equatorward of the equatorial anomalies, or approximately 15 geomagnetic latitude. Here, we present observational evidence from a field-aligned narrowfield imaging system of MSTIDs existing very close to the magnetic equator. We discuss the implications of this observation in terms of the development and propagation of MSTIDs.