Equatorial Electrojet Current System

Abstract

Equatorial electrojet is a day-time enhancement of the normal <i>Sq </i> field in a narrow band of 4-5ᵒ width along the magnetic equator. Its width, intensity, seasonal and sunspot cycle variations over different regions of the earth have been discussed. The <i>Sq </i> ranges in H along the electro jet show equinoctial maxima and solsticial minima. The <i>Sq </i> (<i>Z</i>) variations are asymmetric with respect to the magnetic equator. The lunar daily variations are also abnormally large in the electrojet region. The seasonal variation of <i>L₂</i>(<i>H</i>) in the electrojet region is larger than the <i>Sq</i>(<i>H</i>) and it differs from the <i>Sq </i>pattern with maximum amplitude in December solstice. On certain 'big <i>L </i> days', the electrojet modifies <i>Sq</i>. The <i>DS </i>currents, return currents of the DP substorms, are enhanced in the electrojet region. The irregular fluctuations during magnetic storms are also enhanced. The <i>Dst </i>field in the initial phase of the storm also gets enhanced; in the recovery phase, <i>a_p </i> recovers more quickly than <i>Dst. </i> The physical processes in the ionosphere leading to the equatorial electrojet and a critical appreciation of the theoretical models are given. Meridional currents, observable on the ground, under the electrojet have been computed and it is estimated that the meridional electric field forms 5-10% of the E-W electric field. The results of rocket observation of the electrojet are also summarized.