Equatorial electrojet observed by low inclination orbit satellites: multiple cases study

Recent studies based on magnetic field measurements from low altitude orbit satellites (e.g., CHAMP, Swarm) have improved the understanding of the equatorial electrojet (EEJ). With the successful launch of the Low Orbit Pearl Satellite series (LOPS) (Zhu et al. in Geosci. Instrum. Method. Data Syst. Discuss. 2021:1-27, 2021), we could study the characteristics of EEJ with low inclination satellites. The main field, crustal field, and the magnetospheric field, calculated from the CHAOS-7 model (Finlay et al. in Earth Planets Space 72(1):156, 2020), are subtracted from the original data. The solar quiet daily variation signals are removed by subtracting the spherical harmonic polynomial fitting. We studied four cases where the peak of inverted EEJ current density locates 1 to several degrees northward from the dip equator. The deviation of the peak from the dip equator might depend on longitude or season. Another case including three crossings from one constellation is studied together to reduce noise. Multiple cases study shows that the peak north component of the magnetic field generated by the EEJ is about 24 nT at 600 km altitude. The EEJ current density is inverted by assuming multiple parallel eastward line currents. The current density peaks at 0.12 A/m with a half-width of 5 degrees. It is also found that the EEJ is asymmetric to the dip equator where the peak of the EEJ current density is about 1.5 degrees north of the dip equator. More simultaneous observations from LOPS will be used to investigate the small-scale structure of EEJ in future studies.