Measurements of total electron content near the magnetic equator

Abstract

The columnar electron content, nT, has been measured at Zaria for a 9-month period by the ‘close-spaced frequency’ method using the 40 and 41 Mc/s transmissions from the beacon satellite S-66 (BE-B). The ‘diurnal’ variation of nT for periods of local summer, spring equinox, and local winter show double-peaked daytime maxima, somewhat similar to those for NmF, the peak electron densities. An explanation is proposed in terms of the diurnal development of the equatorial geomagnetic anomaly in the F-region and this is also thought to explain the large values of scale height observed in the period 09–15 hours. The early morning peak in scale height is thought to be caused by ionization of the topside ionosphere prior to ground sunrise.