Speaker
Description
Geomagnetic field reversal sequences exhibit inter-reversal, or persistence, times spanning a broad range, from a few 10⁴ years to superchrons lasting more than 10⁷ years. Statistical analyses show that the reversal sequence does not follow a simple Poisson process with a constant rate and displays signatures of memory, clustering, and heavy-tailed behaviour. Short persistence times display irregular fluctuations consistent with chaotic dynamics, while long intervals reflect the presence of a metastable large-scale dipole state with memory or clustering component. Paleomagnetic data therefore support the interpretation of the geodynamo as a bistable system subject to internal turbulent fluctuations and possibly influenced by weak periodic components.
In this framework, we adopt a simplified low-dimensional dynamo model in which a shell model represents the turbulent convective motions driving magnetic-field generation. Bistability is introduced through a pitchfork bifurcation term in the large-scale magnetic-field equation, controlled by a parameter related to the kinetic helicity. A slow periodic modulation of this parameter, consistent with long-term variations in the heat flow across the core–mantle boundary (CMB), reproduces the key signatures of stochastic resonance, a mechanism proposed to explain the statistical properties of geomagnetic field reversals.
Our results highlight the combined roles of thermal forcing, helicity variations, and turbulence in shaping dipole variability, providing new insights into the physical origin of geomagnetic reversal statistics and, more generally, magnetic-field variability in planetary dynamos.
