Seasonal variation of inter-hemispheric field-aligned currents deduced from time-series analysis of the equatorial geomagnetic field data during solar cycle 23–24

• Published in: Earth, planets, and space planets, and space, 2021-07, Vol.73 (1), p.1-10, Article 146
• Main Authors: Ranasinghe, Manjula, Fujimoto, Akiko, Yoshikawa, Akimasa, Jayaratne, Chandana
• Format: Article
• Language: English
• Subjects: 3. Space science; Amplitudes; Asymmetry; Earth and Environmental Science; Earth Sciences; Equatorial magnetic field; Express Letter; Field aligned currents; Geology; Geomagnetic field; Geomagnetic latitude; Geomagnetism; Geophysics/Geodesy; Ground-based magnetometer data; Ground-based observation; Inter-hemispheric field-aligned currents (IHFACs); MAGDAS/CPMN; Magnetic fields; Observations; Polarity; Satellite observation; Seasonal variations; Solar activity; Solar cycle; Solar cycle SC23 and SC24; Solstices; Time series
• ISSN: 1880-5981; 1343-8832; 1880-5981
• DOI: 10.1186/s40623-021-01481-6

The east–west component of magnetic field variation (∆ D -component) at Davao station (Philippines, geomagnetic latitude: – 2.22˚N) are used to investigate the characteristics of the long-term Inter-Hemispheric Field-Aligned Currents (IHFACs) based on the time-series analysis from August 1998 to July 2020. Recent in situ satellite and ground-based observations have reported that dusk-side current polarity of IHFAC is often opposite to that of the noon IHFAC, being inconsistent with Fukushima's IHFACs model. We investigated the consistency of the dusk-side IHFAC polarity derived from the observations with the polarity expected from Fukushima’s IHFACs model and examined the solar cycle dependence of IHFACs. It was confirmed that the dusk-side IHFACs during June and December solstices flow in the same direction of the noontime IHFACs, which was consistent with the IHFAC polarities suggested by the Fukushima model. The dusk-side IHFACs around March and September–November months disagreed with the Fukushima model. The ∆ D variations clearly showed seasonal asymmetry in the dawn and noon sectors, whereas the ∆ D variations in the dusk sector demonstrated seasonal symmetry. Solar cycle dependence of IHFACs was exhibited in the dusk sector. For the dawn and noon sectors, the yearly peak-to-peak ∆ D amplitude in the later solar cycle SC24 decreased by about 35% in comparison with the earlier solar cycle SC23. In contrast, the dusk-side yearly peak-to-peak ∆ D amplitude increased by about 200%. The dusk-side IHFAC yearly amplitude tended to be in inverse proportion to solar activity.