Counter-electrojet and Esq disappearance

Abstract

The disappearance of Esq type traces from ionograms at the magnetic equator during magnetically quiet periods is related to inverted latitudinal profiles of the regular daily magnetic S_R variation (in its horizontal and vertical components). Latitude profiles obtained from a meridian chain of nine magnetometers across central Africa are compared with corresponding quarter-hourly ionogram sequences from Fort-Archambault-Sarh (Chad). Between 0900 and 1500 LT, the magnetic reversal coincides exactly with the disappearance of Esq traces. This evidence gives additional weight to the hypothesis of a counter-electrojet current belt, located on exactly the same latitudes as the normal electrojet and probably flowing below it at the bottom of the E-layer. It agrees well with present theory on type II slow turbulent modes, and confirms the V_eΛB plasma instability mechanism as the cause of Esq inhomogeneities at this level.