Theory of longitudinal gradients in the equatorial electrojet

Abstract

Longitudinal gradients in the equatorial electrojet are observed with scales ranging from several thousands of kilometers on down. Since previous theoretical models of the electrojet electric fields and currents have assumed that no longitudinal gradients exist, we examine theoretically the consequences of allowing for them. The vertical structures of the electric fields and currents are altered in predictable ways, the alterations being increasingly important as the electric field and current gradients increase. In contrast to the infinite-electro jet model, reversals of the electric field and current directions with height become possible when longitudinal gradients are present. We show how electric fields produced by hypothetical generating sources located at various latitudes are attenuated between the source and the Equator. For electric fields with small longitudinal scale lengths, the source must lie close to the magnetic equator in order to cause noticeable effects in the electrojet.