Day‐to‐day variability of equatorial electrojet and its role on the day‐to‐day characteristics of the equatorial ionization anomaly over the Indian and Brazilian sectors

Abstract

The equatorial electrojet (EEJ) is a narrow band of current flowing eastward at the ionospheric E region altitudes along the dayside dip equator. Mutually perpendicular electric and magnetic fields over the equator results in the formation of equatorial ionization anomaly (EIA), which in turn generates large electron density variabilities. Simultaneous study on the characteristics of EEJ and EIA is necessary to understand the role of EEJ on the EIA variabilities. This is helpful for the improved estimation of total electron content (TEC) and range delays required for satellite‐based communication and navigation applications. Present study reports simultaneous variations of EEJ and GPS‐TEC over Indian and Brazilian sectors to understand the role of EEJ on the day‐to‐day characteristics of the EIA. Magnetometer measurements during the low solar activity year 2004 are used to derive the EEJ values over the two different sectors. The characteristics of EIA are studied using two different chains of GPS receivers along the common meridian of 77°E (India) and 45°W (Brazil). The diurnal, seasonal, and day‐to‐day variations of EEJ and TEC are described simultaneously. Variations of EIA during different seasons are presented along with the variations of the EEJ in the two hemispheres. The role of EEJ variations on the characteristic features of the EIA such as the strength and temporal extent of the EIA crest has also been reported. Further, the time delay between the occurrences of the day maximum EEJ and the well‐developed EIA is studied and corresponding results are presented in this paper.

Statistical analysis of the correlation between the equatorial electrojet and the occurrence of the equatorial ionisation anomaly over the East African sector

“…To obtain the EEJ ( H ), the H S values calculated at ETHI were subtracted from those of the corresponding days that were calculated at AAE. Most studies on the EEJ report the peak of the diurnal EEJ around 12:00 LT (Gouin, 1962;Venkatesh et al, 2015;Yizengaw et al, 2014;Subhadra Devi and Unnikrishnan, 2014). In line with this information, the daytime EEJ strength for each day in this study was represented by the mean of the EEJ during the period 10:00-13:00 LT, when the peak of the daytime EEJ is expected to occur.…”

“…Various authors have found different time delays that exist between intense EEJ strength and the occurrence of the prominent EIA. For instance, an approximate time delay of 2-3 and 4 h were reported by Rush and Richmond (1973) and Venkatesh et al (2015), respectively. Since the peak of the EEJ occurs at around 12:00 LT, the cases of prominent EIA about 8 h later (during 20:00-24:00 LT) might not be due to increased zonal electric fields associated with increased EEJ.…”

“…In the second analysis, we computed the EIA strengths. Various studies have represented EIA strength in many ways, including (i) computing the difference of TEC measured at the crest and that at the trough (Sastri, 1982), (ii) determining the normalised difference of TEC measured at the crest and that measured at the trough (Sastri, 1982), (iii) simply using the peak of TEC measured at the crest (Venkatesh et al, 2015) and (iv) determining the ratio of TEC measured at the crest to that measured at the trough (Zhang et al, 2009;Yue et al, 2015), referred to as the CT : TEC ratio. Unlike methods (i) and (ii) which might produce both negative and positive EIA strengths, the last two methods only yield positive values.…”

“…Due to such problems, several studies have been undertaken to understand the influence of the EEJ on the development of the EIA. Most of the studies related to the development of the EIA and EEJ have been done over American and Indian longitude sectors (Sethia et al, 1980;Chakraborty and Hajra, 2009;Hajra et al, 2009;Zhang et al, 2009;Yizengaw et al, 2010;Venkatesh et al, 2015;Rodriguez-Zuluaga et al, 2016). There are also some studies that have used global data to study the morphology of the EIA.…”

GPS-TEC Variation during Low to High Solar Activity Period (2010-2014) under the Northern Crest of Indian Equatorial Ionization Anomaly Region

“…in Africa, [8]- [13], in South America, [14] [15] [16] [17] [18] over China [19] [20], Huo et al [21] and Perevalova et al [22] over North America, Zakharenkova et al [23] over Japan; Venkatesh et al [24] [25] [26] over Brazil and many more. Ionospheric TEC variations have been investigated in the Indian region, using this data and other separate TEC measurements at Surat [27], Agra [28] and other different stations, namely Trivandrum, Waltair, Raipur and Delhi [6].…”