A Dynamical Prospective on Interannual Geomagnetic Field Changes

Abstract Geomagnetic observations from satellites have highlighted interannual variations in the rate of change magnetic field originating Earth’s core. Downward continued to core surface, these primarily show up equatorial belt. First, we recall main characteristics patterns, addressing their spatio-temporal resolution, as seen models. We then review several dynamical frameworks proposed so far understand and model observations, which populate frequency spectrum on time scales close Alfvén $$\tau _A\approx 2$$ ? A ? 2 yr, much shorter than vortex turnover _U\approx 150$$ U 150 yr Magnetic–Archimedes–Coriolis (MAC) waves a stratified layer below surface constitute first possibility case sub-adiabatic heat flux at top Their period may reach range for thickness less $$\approx 30$$ 30 km, buoyancy order rotation rate. An alternative has been context where Coriolis force dominates momentum balance, rendering transient motions almost invariant along axis (quasi-geostrophy, QG). Torsional waves, consisting axisymmetric QG motions, operate periods similar time, but are not sufficient explain changes, require non-axisymmetric motions. (involving forces) another possibility, with inertia playing an important role. They detected latest generation geodynamo simulations, propagating ubiquitous manner speed slightly velocity. localized longitude result description requires high azimuthal wavenumber. But branch large extent azimuth is also worth considering, it reaches radial wavenumber increased. The excitation such high-frequency dynamics discussed respect temporal field, presents slope $$\sim f^{-4}$$ ? f - 4 approximately between _A$$ _U$$ . finally summarize geophysical implications existence this lower mantle structure, properties, dynamics.