The equatorial ionospheric electric fields. A review

Abstract

The equatorial electric fields have been extensively studied over the last decade using radio, radar and rocket observations. Radar measurements of vertical and east-west F-region drift velocities at Jicamarca have determined the seasonal and solar cycle variations of the F-region east-west and vertical electric fields, respectively. Rocket observations during twilight indicate the existence of a shear in the east-west drifts with eastward velocities near and above the F-region density peak and westward velocities in the lower F-region where incoherent scatter radar observations are not effective. The vertical drift (i.e. east-west electric field) changes considerably with magnetic activity, but the F-region east-west drift (vertical electric field) is not affected. During magnetically disturbed periods the zonal equatorial electric field shows frequent and large fluctuations indicating the penetration of magnetospheric electric fields into the low-latitude ionosphere. The coupling processes are not yet totally clear. Considerable progress has been made recently in the understanding of these quiet-time and disturbed equatorial electric fields.