Latitude variation of total electron content in the equatorial region

Abstract

Appleton [1946] showed that in the equatorial zone the ionization of F2 layer exhibits a marked latitude dependence, the ionization being minimum at dip equator and maximum at ±20–30° dip. Further, this anomalous behavior of F2 layer, known as the equatorial anomaly, is most prominent around noontime and hardly noticeable in the early morning and late evening hours. Recently, the topside sounder data [Van Zandt et al., 1965] have exhibited that the above equatorial anomaly is not confined to a narrow height range around the F2 layer but extends well up to 600 km, and the peaks of ionization are aligned along a magnetic field line of the earth. It is, therefore, expected that the total electron content of the ionosphere measured with the help of beacon satellites should show such a latitude dependence.