On the nature of equatorial slant sporadicE

Two features of the daytime sporadic E echoes observed on ionograms obtained near the magnetic equator have been termed ‘equatorial sporadic E’ and ‘equatorial slant sporadic E.’ These are traces that project from the E-layer trace and have equivalent ranges independent of frequency and proportional to frequency, respectively. Radar studies in Peru indicate that a thin stratum of magnetic-field-aligned irregularities embedded in the E layer is responsible for the entire sporadic E configuration. The increased equivalent ranges of the slant trace are attributed to oblique propagation in the east-west plane orthogonal to the irregularities. By accounting for the refraction and retardation imposed by the E layer, the entire configuration can be simulated in detail. It is established from this analysis that the equatorial electrojet flows within the equatorial E layer, and that its first-order current variations are coherent over distances of 500 km or more along the magnetic equator.