Electrojet control of ambient ionization near the crest of the equatorial anomaly in the Indian zone

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%).

Investigation of TEC variations over the magnetic equatorial and equatorial anomaly regions of the African sector

“…Ionospheric TEC values exhibit significant variations with solar cycle, season, local time, altitude, latitude, longitude and geomagnetic activity (Sardar et al, 2012). The Earth's ionosphere along the equatorial (low latitude) region is quite unique and different from that at the mid and high latitudes (Chakraborty and Hajra, 2009). This is because the low latitude ionospheric F-region is dominated by a phenomenon called equatorial ionization anomaly (EIA), which is characterized by an electron density trough region around the magnetic equator, and a dual band of enhanced electron density (crest regions) at about 15 north and south of the trough as shown in Fig.…”

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

“…TEC deviations are plotted against the EEJ values. An approximate time delay of~2 h between the cause (triggering of the equatorial fountain) and the effect (changes in ambient level near the anomaly crest) is incorporated in the selection of EEJ values (Rush & Richmond 1973;Sethia et al 1980;Chakraborty & Hajra 2009). Figure 5 shows sample plots of the TEC variation with EEJ (linear regression fitting) for the months of January, July, and October (Eq.…”

NmF2 and hmF2 measurements at 95° E and 127° E around the EIA northern crest during 2010–2014

“…In December solstice, the midnight values of hmF2 are higher than those of daytime maximum hmF2 and this behavior is reminiscent of mid-latitude stations (Mikhailov and Marin 2001;Liu et al 2007b;Ratovsky and Oinats 2009). It has been reported by number of workers that in the Indian zone, the crest of the EIA recedes in December solstice to~10°N geomagnetic (Rastogi et al 1972;Bhuyan et al 2003;Chakrabarty and Hajra 2009). From the analysis, we may suggest that during December solstice, Dibrugarh/Okinawa behave like mid-latitude stations, whereas in other seasons, they behave more like low-latitude stations.…”