Excursions of Interhemispheric Field‐Aligned Currents in Africa

Abstract

The interhemispheric field‐aligned currents (IHFACs) are the most evident currents connecting the solar quiet (Sq) current systems in the Northern and Southern Hemispheres. Understanding these coupling currents has practical importance for space weather forecast of the magnetosphere‐ionosphere interactions and their potential impacts on low‐orbiting spacecraft. In this paper, we have examined digital magnetic records from September 2008 to August 2009 at nine Magnetic Data Acquisition System (MAGDAS) stations in order to uniquely determine the variability of IHFACs in terms of their excursions in the African sector. By excursions, we mean the direction in which the IHFACs are moving as a function of local time or latitude. Different from theoretical prediction, we found prominent positive IHFACs around dusk in February and March equinox. A novel feature of this study is the semidiurnal variation control of the coupling between the Northern and Southern Hemispheres. In addition, we found terdiurnal variation in September with their associated strong diurnal variations from October through December. Quite unexpectedly, in January, a significant latitudinal depletion in the intensities of IHFACs was observed from dawn to dusk, compared to any other months under investigation, accompanied with a marked reduction of the prominent diurnal variations at the magnetic equator (Addis Ababa, AAB). The fact that the excursions of IHFACs in January experience an unusual retardation with respect to their intensities points to a relation with the effects of sudden stratospheric warming.

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

“…The first experimental evidence has been provided from Magsat observations (Olsen 1997). The characteristics of IHFACs have been extensively described by many papers, for example, seasonal climatology of IHFACs by the Ørsted satellite (Yamashita and Iyemori 2002), seasonal, longitudinal, and local-time IHFACs variations by the CHAMP satellite (Park et al 2011) and the Swarm satellite constellation (Lühr et al 2015(Lühr et al , 2019Fathy et al 2019;Park et al 2020b), ground-based local-time and seasonal dependence (Bolaji et al 2012;Shinbori et al 2017;Abidin et al 2019) and latitudinal dependence (Owolabi et al 2018).…”

Latitude Dependence of Interhemispheric Field‐Aligned Currents (IHFACs) as Observed by the Swarm Constellation

“…Though the IHFACs have been studied extensively using ground‐based (e.g., Bolaji et al, ; Owolabi et al, ; Shinbori et al, ) and satellite‐based magnetic field observations (e.g., Lühr et al, , ; Olsen, ), there is still room for further improvement. First, most of the existing studies on satellite‐based IHFAC data focused on regions near the equator.…”

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

“…The rst experimental evidence has been provided from Magsat observations (Olsen, 1997). The morphology of IHFACs has been extensively described by many papers, for example, seasonal climatology of IHFACs by Ørsted satellite (Yamashita and Iyemori, 2002), seasonal, longitudinal and local-time IHFACs climatology by CHAMP satellite (Park et al, 2011) and Swarm satellite constellation (Lühr et al, 2015;Fathy et al, 2019), ground-based local-time and seasonal dependence (Bolaji et al, 2012;Shinbori et al, 2017;Abidin et al, 2019), latitudinal dependence (Owolabi et al, 2018;Park et al, 2020a).…”

“…In addition, their analysis periods were almost limited to demonstrate the solar cycle dependence of IHFACs, namely less than solar cycle period (11 years) (e.g. Park et al, 2011;Owolabi et al, 2018;Lühr et al, 2019). Shinbori et al (2017), only, used long-term (59 years) ground-based magnetometer data for the comparison of IHFACs intensity between higher and lower solar activity periods.…”