Geomagnetic reversals and excursions as an outcome of non-equilibrium bulk turbulence in the Earth’s core

Summary We investigate the effect of statistically non-stationary turbulence in the Earth’s outer core on the effective turbulent electromotive force generated by the convectively driven flow of liquid iron and the evolution characteristics of the geomagnetic field. The non-stationarity means that interactions of distinct waves are crucial, and the effect of beat induces a slow time variation of the large-scale electromotive force. This provides an attractive and fairly simple physical mechanism for the random appearance of short-lived geomagnetic excursions and reversals separating long periods of relatively stable field, through non-synchronized evolution of the amplifying α-effect and turbulent diffusion. This implies rare and random appearance of simultaneous suppression of the α-effect and enhancement of diffusion which leads to a sudden magnetic energy drop, i.e. an excursion. The turbulent field of what is termed MAR waves (Magnetic-Archemedean-Rossby) is analysed. The dispersion relation and structure of such waves involving the joint effect of the Lorentz, buoyancy, and Coriolis forces together with curvature of the core-mantle boundary are obtained and utilized for estimation of the non-stationary electromotive force in the core. The solutions for the large-scale dipole possess an Earth-like behaviour, magnitude, and timescales, and the physical mechanism of the process, including identification of two dynamically important parameters, is discussed. Similar ideas concerning the dynamics of waves within the so-called Stratified Ocean at the top of the Core (SOC) were considered in the recent work Mizerski (2025). The SOC is an important but thin, strongly stratified layer near the core-mantle boundary, and here, the possibility of global non-equilibrium dynamo mechanisms is analysed. It is possible that the surface and bulk mechanisms coexist in the core, both adding to the complexity of the observed picture of reversal occurrences.