Equatorial counter-electrojet and the F2-layer of the ionosphere

Abstract

It is shown that the quiet day afternoon counter-electrojet events at equatorial stations are the result of a strong semi-diurnal tidal force, with a maximum around 0900 LT and a minimum around 1500 LT, superimposed over the normal Sq (H) variation. This additional eastward electric field in the forenoon hours over the magnetic equator is shown to cause an enhancement of the equatorial F-layer plasma fountain, and results in a lower ƒoF2 at the equator. The daily variation of the differential values of ƒoF2, being almost counter-electrojet minus normal electrojet days, and in antiphase with the corresponding curve of ΔH. At the anomaly crest station, larger values of ƒoF2 are observed in the afternoon on counter-electrojet with a delay of about 3 h with respect to the decrease of ƒoF2 at the equator.