Counter electrojet and Esq disappearance

Abstract-The disappearance of Esq type traces from ionograms a t the magnetic equator during magnetically quiet periods is related to inverted latitudinal profiles of the regular daily magnetic 8, variation (in its horizontal and vertical components). Latitude profiles obtained from a meridian chain of nine magnetometers across central Africa me compared with corresponding quarter-hourly ionogram sequences from Fort-Archambault-Sarh (Chad). Between O900 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 Ve A B plasma instability mechanism as the cause of Esq inhomogeneities at this level. 1