The impact of century-scale changes in the core magnetic field on external magnetic field 1

10 The Earth’s internal magnetic field controls to a degree the strength, geographic positioning, and 11 structure of currents flowing in the ionosphere and magnetosphere, which produce their own 12 (external) magnetic fields. The secular variation of the Earth’s internal magnetic field can therefore 13 lead to long-term changes in the externally produced magnetic field as well. Here we will examine this 14 more closely. First, we obtain scaling relations to describe how the strength of magnetic perturbations 15 associated with various different current systems in the ionosphere and magnetosphere depends on 16 the internal magnetic field intensity. Second, we discuss how changes in the orientation of a simple 17 dipolar magnetic field will affect the current systems. Third, we use model simulations to study how 18 actual changes in the Earth’s internal magnetic field between 1908 and 2008 have affected some of 19 the relevant current systems. The influence of the internal magnetic field on low- to mid-latitude 20 currents in the ionosphere is relatively well understood, while the effects on high-latitude current 21 systems and currents in the magnetosphere still pose considerable challenges.

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