Equatorial E region irregularities: a review of recent observations

The recent observations on the small-scale irregularities in the equatorial E region from locations other than those from the close vicinity of the electrojet (EJ) centre are reviewed. In particular, the diurnal characteristics of irregularities at low latitudes (>±4.5°) off the EJ centre at the dynamo heights reveal that they occur usually in the forenoons and afternoons and not around the noon hours when the EJ is most intense. These features are interpreted, by the EJ model calculations, as due to the electric fields and current densities engendered by the vertical shears in zonal winds (J. Geophys. Res. 92 (1987) 2514). The observational results on the '150km' irregularities are critically reviewed from the points of view of the respective causative mechanisms suggested earlier