Day-to-day changes in ionospheric electron content at low latitudes

The day-to-day variability in ionospheric electron content (IEC) is studied using the diurnal IEC maximum data obtained from multistations located in the latitude range between 15.0°N and 30.0°N in the Indian zone during solar minimum. Depending on the location of the observing station, the changes in IECmax values, of about ±20 to 40%, are found to occur in the form of single day abnormality, alternate day abnormality, and long-term periodic fluctuations. The magnitude of fluctuations is found to be maximum at a station which is near the crest of the equatorial anomaly belt. The long-term periodic variations, other than annual and semiannual variations, are different for different locations and seasons and show a periodicity of about 45 days in winter in the equatorial anomaly region only and about 27 days in summer at all the stations. The changes are not always correlated with solar or magnetic activity changes. It is observed that short- as well as long-term variations in IECmax at stations within and near the crest of the equatorial anomaly belt are controlled mainly by the electrojet strength variation.