On the equatorial anomaly of the ionospheric total electron content near the northern anomaly crest region

Daily contour charts of the ionospheric total electron content in latitude versus local time coordinates have been used to study the behavior of the development of the equatorial anomaly around the northern anomaly crest region. The daily development of the equatorial anomaly shows quite large day-to-day variabilities not only on magnetically disturbed days but also on quiet days. The daily maximum anomaly crest moves poleward as the magnitude of the total electron content of the daily maximum anomaly crest increases. The increase of the equatorial electrojet strength also results in a poleward movement of the anomaly crest. No significant correlation exists between the anomaly crest and the magnetic Ap index. The monthly mean diurnal development of the equatorial anomaly shows a remarkable seasonal difference, with the anomaly largest in equinoxes and slightly larger in winter than in summer. copyright American Geophysical Union 1989