Influence of dawn and dusk conductivity on the equatorial electrojet

A reason for the presence of an ionospheric electrostatic field is discussed briefly, and the surface charge densities are evaluated for the case of a conductivity discontinuity. The resulting formulae are used to discuss qualitatively the equatorial electrojet properties at dawn and dusk. It will be shown that these parts of the electrojet current system vertical currents must be present. A reversed but more diffuse current is supposed at lower heights.