Climatology of the inter-hemispheric field-aligned current system in the equatorial ionosphere as observed by CHAMP

Abstract

Abstract. From geomagnetic field observations of CHAMP during [2001][2002][2003][2004][2005][2006][2007][2008][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.

The ionospheric Sq current system obtained by spherical harmonic analysis

“…[60] It is noticeable in Figure 10 that the positive ΔD, southward flow, in December is centered around 15 LT, rather than noon, and this closely agrees with the results of Park et al [2011].…”

“…Noon FACs are deduced from the tilt of the current system. Afternoon/dusk results are harder to interpret: it seems that our results agree more closely with the Fukushima model than with the satellite results of Park et al [2011], though the satellite currents are earlier in local time.…”

“…[63] The presence of FACs in September, as indicated in Figure 1c, can be also seen in the results of Park et al [2011] and of Yamashita and Iyemori [2002]. In particular, Park et al [2011, Figure 3] showed a FAC in September at 315…”

“…The very small northward current off the coast of Western Australia at around 19 h LT shown in Figure 9 would fit the pattern suggested by Fukushima [1994], but examination of the ΔD variation at Gnangara (31.8 S,115.9 E) in Western Australia also shows a negligibly small deviation at this time. A southward current, as observed by Park et al [2011] at the earlier time of 16-17 h LT, would be hard to detect because that is the direction of the "normal" Sq currents at dusk in the Southern Hemisphere.…”

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…Yamashita and Iyemori (2002) analyzed magnetic data from the Ørsted satellite to study the seasonal climatology of the inter-hemispheric field-aligned currents. Park et al (2011) showed a comprehensive seasonal, local-time and longitudinal climatology of the inter-hemispheric field-aligned currents based on 9 years of magnetic field measurements by the CHAMP (CHAllenging Minisatellite Payload) satellite. Lühr et al (2015) used measurements from the Swarm satellite constellation.…”