Abstract
In this study, the seasonal variations of the EEJ longitudinal profiles were examined based on the full CHAMP satellite magnetic measurements from 2001 to 2010. A total of 7537 satellite noon-time passes across the magnetic dip-equator were analyzed. On the average, the EEJ exhibits the wave-four longitudinal pattern with four maxima located, respectively, around 170° W, 80° W, 10° W and 100° E longitudes. However, a detailed analysis of the monthly averages yielded the classification of the longitudinal profiles in two types. Profiles with three main maxima located, respectively, around 150° W, 0° and 120° E, were observed in December solstice (D) of the Lloyd seasons. In addition, a secondary maximum observed near 90° W in November, December and January, reinforces from March to October to establish the wave-four patterns of the EEJ longitudinal variation. These wave-four patterns were divided into two groups: a group of transition which includes equinox months March, April and October and May in the June solstice; and another group of well-established wave-four pattern which covers June, July, August of the June solstice and the month of September in September equinox. For the first time, the motions in the course of seasons of various maxima of the EEJ noon-time longitudinal profiles have been clearly highlighted.
Highlights
The equatorial electrojet (EEJ) is a daytime ionospheric current that flows eastward along the magnetic equator at about 105 km altitude (Chapman 1951)
The four maxima located, respectively, at about − 170° E, − 80° E, − 10° E and 100° E longitudes confirm the four-wave structure of the EEJ longitudinal variation, shown in previous studies (Alken and Maus 2007; Doumbia et al 2007; Le Mouël et al 2006; Yamazaki and Maute 2017)
This structure is susceptible to seasonal variations that are examined
Summary
The equatorial electrojet (EEJ) is a daytime ionospheric current that flows eastward along the magnetic equator at about 105 km altitude (Chapman 1951). Most of the EEJ characteristics like day-to-day, seasonal, latitudinal, longitudinal variability and the counter-electrojet phenomenon have been described through its magnetic effect recorded on ground as well as onboard polar orbiting satellites (Cain and Sweeney 1973; Gouin 1967; Gurubaran 2002; Langel et al 1993). 100° E and 180° E (Alken and Maus 2007; Doumbia et al 2007; Doumbia and Grodji 2016; Doumouya and Cohen 2004; Jadhav et al 2002). According to Alken and Maus (2007), Doumbia et al (2007) and Doumbia and Grodji (2016), these longitudinal structures of the EEJ can be subject of seasonal variations. The transitions between the EEJ longitudinal patterns of three maxima and those of four maxima and the background physical processes are not well understood
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