A review of the theories concerning the equatorial F2 region ionosphere

The most striking feature of the equatorial F-region ionosphere is the equatorial geomagnetic anomaly. This phenomenon has been known for nearly thirty years from bottomside measurements, but only recently have topside sounders provided sufficient data for the development of theoretical models. It appears that the major contribution to this effect lies in the interaction of the ionosphere with the earth´s magnetic field via mechanisms causing drifts and currents. However, other theories have considered control due principally to production, loss and temperature effects. This paper reviews relevant theoretical analyses and compares the theoretical predictions with data available from the Alouette I topside sounder.