Ionospheric storm effects at the equatorial anomaly

Abstract

Ionospheric disturbances produced at the equatorial anomaly (EA) region during some geomagnetic storms were investigated using hourly NmF2 peak electron density of F2-layer values from stations located at equatorial and low geomagnetic latitudes. In general, increases (positive storm effects) or decreases (negative storm effects) of NmF2 (proportional to square of foF2 ionospheric critical frequency) in the nighttime hours were observed at equatorial latitudes in response to storms started during sunset hours. For the storm onset occurring during morning hours an intensification of the fountain effect was produced. For the storms starting in the nighttime hours no significant disturbances appeared at the crest regions in association with the initial positive or negative effects observed at the trough in the daytime. During the recovery phase in general significant delayed positive storm effects occurred mainly at low latitudes and a minor degree at equatorial latitudes. Possible physical mechanisms for controlling the morphology of the ionosphere during these events are considered.