Geomagnetic Reversals and Excursions as an Outcome of Non-Equilibrium Wave-Turbulence and Beating MAC Waves in the Core

Abstract

The turbulence in the liquid iron within the outer core of the Earth is responsible for the geomagnetic field generation, its sustainment and dynamical evolution. Here we revive Braginsky's idea of the Stratified Ocean at the top of the Core (SOC) and consider a non-stationary turbulent wave field composed of Magnetic-Archimedean-Coriolis (MAC) waves inside the SOC. The non-stationarity, hitherto ignored, implies non-vanishing coupling of waves with distinct frequencies, in particular the effect of beating waves leading to formation of electromotive force slowly varying in time in the core. It is shown that the beating frequencies, that is small frequency differences between interacting MAC waves can lead to an Earth-like behavior of the large-scale magnetic field, exhibiting long periods of fairly stable field separated by short lived reversals or strong excursions, which appear to be random. Within such an approach the resulting reversals/excursions are simply manifestations of a chaotic turbulent flow inside the core, and no significant alterations of the large-scale flow structures are necessary in order for reversals to occur. Such a dynamical picture seems highly desired since it has been a long-standing puzzle that many previous numerical simulations of the Earth's core dynamo exhibiting magnetic field reversals reported no significant modifications of large-scale flow structures during the process and only local variations in strength of the background small-scale turbulence.