Long-Term Analysis of Day-To-Day Equatorial IHFACs Variations During Solar Cycle 23-24

Abstract The east-west ward variation of MAGDAS/CPMN magnetometer 1-hour time resolution data at Davao (Philippines) station operated by International Center for Space Weather Science and Education, Kyushu University from August 1998 to July 2020 are used to investigate the characteristics of the long-term Inter-hemispheric field-aligned currents (IHFACs). The recent in-situ satellite and ground-based observations have reported the dusk-side current polarity of IHFACs are often inconsistent with the Fukushima’s IHFACs model. We investigated whether the dusk-side IHFACs polarity is consistent or not with the current direction predicted by Fukushima’s IHFACs model, by analyzing the time-series data of the day-to-day IHFACs variations. We confirmed that the solstices dusk IHFACs flow the same direction of noon IHFACs and the equinoxes dusk IHFACs disagree with Fukushima’s model. Seasonal IHFACs variations exhibited remarkable asymmetry in both dawn and noon sectors. By contrast, the profile of dusk-side IHFACs intensity was symmetry. We presented that solar cycle dependence can be seen in the peak-to-peak amplitude, monthly average and yearly integral intensity of IHFACs. However, while the dawn and noon IHFACs intensity decreased with year by year, the dusk intensity tended to increase year-to-year. In contrast to annual variations of IHFACs polarity in the dawn/noon sectors, there were multiple periodicities in the dusk sector: annual variation during the declining phase of solar cycle and semiannual or terannual variations during the increasing and maximum phase. The dusk-side day-to-day IHFACs variations were more coherent with F10.7 variability compared with the dawn and noon sectors. It suggests that the dusk IHFACs is affected by the solar cycle activities.