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

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 foF2 at the equator, the daily variation of the differential values of foF2, 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 foF2 are observed in the afternoon on counter-electrojet with a delay of about 3 h with respect to the decrease of foF2 at the equator. (author)