Abstract
Abstract. From geomagnetic field observations of CHAMP during 2001–2009 we extracted characteristic signatures of inter-hemispheric field-aligned currents (IHFACs) in the equatorial ionosphere. The results are in general agreement with previous observations. Nighttime IHFACs are negligibly small. Solstitial IHFACs flow from the summer to winter (from winter to summer) hemisphere at dawn (around noon). Duskside IHFACs flow southbound irrespective of season. We have also found some new IHFAC properties, which may have been predicted by theories, but are not yet given observational support. IHFACs clearly exhibit a longitude dependence, which is modulated by the South Atlantic Anomaly, the offset between geographic and magnetic equators, and tidal waves. IHFACs show little dependence on the solar cycle. We provide a comprehensive assessment of the IHFAC modulation by non-migrating tides.
Highlights
In the dayside ionospheric E-region there exists a current vortex in each hemisphere, which is known as solar-quiet (Sq) current system (e.g., van Sabben, 1964)
Yamashita and Iyemori (2002) reported an inter-hemispheric field-aligned currents (IHFACs) climatology using data from the Ørsted satellite and world-wide ground geomagnetic observatories. They confirmed that (1) IHFACs flow from summer to winter in the dawn sector, which was predicted by theoretical works (e.g., Takeda, 1982; Fukushima, 1994), and (2) the IHFAC direction change does not occur exactly at equinox epochs and the IHFAC intensity does not peak at solstices
Our results show that IHFACs around noon are more southbound in the longitude range where the magnetic equator is located to the south of the geographic equator
Summary
In the dayside ionospheric E-region there exists a current vortex in each hemisphere, which is known as solar-quiet (Sq) current system (e.g., van Sabben, 1964). Yamashita and Iyemori (2002) reported an IHFAC climatology using data from the Ørsted satellite and world-wide ground geomagnetic observatories They confirmed that (1) IHFACs flow from summer to winter (from winter to summer) in the dawn (noondusk) sector, which was predicted by theoretical works (e.g., Takeda, 1982; Fukushima, 1994), and (2) the IHFAC direction change does not occur exactly at equinox epochs and the IHFAC intensity does not peak at solstices. The magnetic deflections observed on ground cannot separate uniquely the effect of Sq currents from that of IHFACs, which may degrade the quality of IHFAC estimation (Yamashita and Iyemori, 2002) Their ground-based results sometimes show differences from Ørsted observations; e.g., the nighttime IHFAC amplitudes derived by ground-based observations were finite while those derived by Ørsted were negligible.
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