Dilemma of the Equatorial Counter-Electrojet & the Disappearance of E_s-q

Abstract

Disappearances of equatorial sporadic-E (E_s-q) are normally associated with depressions in the geomagnetic <i>H </i> component at the equator and are explained on the basis of the theory of cross-field instabilities. Thus, when the vertical electron density gradient and the Hall polarization field are pointing upwards, they produce E_s-q, while during counter-electrojets, if the vertical gradient has the same sign and the electric field reverses, E_s-q disappears. It is shown here that on many occasions, E_s-q disappears even when the normal electrojet (as indicated by ground <i>H </i> variation) does not reverse but only weakens. On many of these occasions the E- and F-region drifts measured by the 3-spaced receiver technique seem to have <i>reversed. </i> To explain this it seems necessary to invoke a sandwich of opposing current systems in the electrojet region. If true, this would be a very baffling situation indeed and needs a thorough experimental and theoretical investigation.