Total Electron Content Studies in Equatorial Regions

Abstract

This paper reviews current knowledge of the diurnal variation and spatial distribution of total electron content in the equatorial ionosphere. The problems of data reduction peculiar to stations near the equator are considered. There is a large diurnal variation up to 40∶1 that is greatest at the equinoxes and least in local winter. An ‘equatorial anomaly’ in total electron content similar to the anomaly observed in f0F2 exists and is largely associated with the topside. Considerable differences in detail, particularly with regard to the time of disappearance of the anomaly, occur at different longitudes. Peaks of ionization have been observed around 2300 LT at about 26° of magnetic dip. Although little correlation has been found with magnetic activity on individual days, collective data indicate a reduction in the depth of the equatorial trough with magnetic disturbances, with the maxima occurring closer to the dip equator. More detailed work is indicated on the effects of longitude and magnetic activity, on the nighttime content, and on large‐scale irregularities.