Storm effects of ionospheric total electron content /TEC/ at low latitudes

Changes in the ionospheric total electron content (TEC), obtained by the Faraday rotation method at several low-latitude stations in India (about 75 deg E), are studied during selected geomagnetic storms in the winter 1975-76. The Group delay method was also used to obtain TEC data near the dip equator in India, and gave similar results. Large changes in ionospheric TEC were noted at low and equatorial latitudes, even in the pre-storm period; these were often at least as large or even larger than those observed during storms. The changes could be positive as well as negative at the crests, and when considered in conjunction with the equatorial electron density and TEC changes, as well as with changes in the equatorial electrojet strength, often showed a pattern consistent with the fountain effect; in other cases, however, the fountain effect was largely distorted. It is concluded that, apart from electric field effects, neutral winds, not only of polar but of low-latitude origin as well, create large dynamic upheavals in the low-latitude ionospheric regions, often in a random fashion, not only during geomagnetic storms, but even before or long after the storms begin.