Publications

Although satellite electromagnetic induction studies have usually assumed a symmetric magnetospheric ring current source described by Y10, there is growing evidence for significant source asymmetry. Balasis et al. (2004) and Balasis and Egbert (2006) presented evidence for at least an additional Y21 quadrupole term that introduces some local time asymmetry in the source. This component is correlated with the traditional axial dipole source variations, and oriented so that meridional magnetic fields peak in the dusk sector (at 19:30 LT). The time-domain, spherical harmonic-finite element method developed by Velimsky and Martinec (2005) has recently been applied to 1-D inverse modeling of CHAMP satellite data assuming only storm-time, axially symmetric ring-current excitation (Velimsky et al., 2006). We attempt to apply the method to model the electromagnetic response of the Earth to the source field incorporating higher degree non-zonal terms. It is noted that a multi-satellite mission would offer the opportunity to compare and combine simultaneous measurements over different local times. This could help in mapping more accurately the fields of the system of external currents used for estimating electromagnetic induction transfer functions. Therefore the foreseen SWARM constellation will be essential to the task of developing improved source models for induction studies. Ultimately, data assimilation methods which combine physics-based models of the magnetosphere and ionosphere with all available data offer the greatest hope for accurate modeling of external sources for global inductionstudies with satellite data.

---

Balasis, G.; Velimsky, J.; Martinec, Z.; Egbert, G. D.; Daglis, I. A.; Eftaxias, K. (2007): Global electromagnetic induction studies in the frame of the SWARM mission. 24th IUGG 2007 (Perugia, Italy, 2007).