Study of the Equatorial Ionosphere: The Equatorial Evening Minimum in the Total Electron Content of the Ionosphere and Its Role in Equatorial Scintillation

A minimum in the total electron content of the equatorial ionosphere frequently appears shortly after sunset in measurements of Faraday rotation made at Legon, Ghana (latitude 5.63 deg N, longitude -0.19 deg E, magnetic dip 8 deg S). This paper describes the phenomenon and investigates its occurrence characteristics over a period of six years. It concludes that the effect is due to a transport phenomenon described as a 'circulation cell' which follows the sunset line. This circulation is not considered to be the primary cause of the production of irregularities in the night time F region, but the mechanism is thought to contribute both to the intensity and the duration of the resulting scintillation. (Author)