Abstract
Abstract. A long-term (1978–1990) database of total electron content (TEC) from a location (Calcutta: 22.58° N, 88.38° E geographic, dip: 32° N) near the northern crest of the equatorial ionization anomaly has extensively been studied to characterize the contribution of fountain effect in the maintenance of ambient ionization. The equatorial electrojet (EEJ) data obtained from ground magnetometer recording are used to assess the contribution of equatorial fountain. Analysis made with instantaneous values, day's maximum values and time-integrated values of EEJ strength exhibit more or less similar features. When instantaneous values of EEJ are considered TEC variations exhibit two maxima in correlation, one around 10:00–12:00 IST and the other around 18:00–20:00 IST. The later maximum in correlation coefficient is conspicuously absent when integrated values of EEJ are considered. An impulse-like feature is reflected in the diurnal TEC variation during the time intervals (09:00–10:00 IST) and (18:00–19:00 IST). The statistical analysis reveals greater correspondence with high level of significance between diurnal TEC and EEJ in the descending epoch of solar cycle than in the ascending one. On the seasonal basis, TEC in the summer solstitial months are observed to be more sensitive to the changes in EEJ strength than in the equinoctial and winter solstitial months. Combining the effects of solar flux, season, local time and EEJ an empirical formula for monthly mean diurnal TEC has been developed and validated using observed TEC data. An estimation of the relative contributions of the several terms appearing in the formula reveals much more solar flux contribution (~50–70%) in the maintenance of ambient ionization around the present location than the EEJ effects (maximum~20%).
Highlights
The equatorial electrodynamics plays a vital role in the distribution of ionization at the low latitude ionosphere
The daytime E-region electric field driven by neutral wind dynamo (Rishbeth, 1971) is the triggering force for the EEJ and the strength of EEJ is influenced by the conductivity of that region
The correlation maxima obtained in the later period may be related to the day’s EEJ strength while the former cases may be attributed to the initial surge developed by the fountain effect in the steady rate of solar flux dominated total electron content (TEC) variability
Summary
The equatorial electrodynamics plays a vital role in the distribution of ionization at the low latitude ionosphere. Some studies exhibited better correspondence between TEC variability and integrated EEJ from low latitude region (Rama Rao et al, 2006). All these studies are based on short-term databases and most of the studies considered daily maximum value as a measure of EEJ strength. In the present investigation a long-term (1978–1990) database of TEC from a station (Calcutta, 22.58◦ N, 88.38◦ E geographic, dip: 32◦ N), situated virtually below the northern crest of the equatorial anomaly, has been analyzed in conjunction with the EEJ data to make qualitative and quantitative estimates of relative contributions of fountain effect, considering EEJ as proxy index, in the distribution of ambient ionization near the anomaly crest. Under present investigation magnetometer horizontal intensity data of Trivandrum, an electrojet station (geographic: latitude 8.29◦ N, longitude 76.57◦ E; dip: 1.2◦ S) and Alibag, outside the EEJ belt (geographic: latitude 18.63◦ N, longitude 72.87◦ E; dip: 23◦ N) are considered
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