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Simple stochastic model for geomagnetic excursions and reversals reproduces the temporal asymmetry of the axial dipole moment

Significance The geodynamo, the process that produces and controls the evolution of the Earth’s magnetic field, is still not fully understood. Despite the success of current numerical geodynamo models in reproducing some geomagnetic observations, their high complexity and computational requirements hinder their use for certain studies. Here, we present a simple model based on random fluctuations that is able to reproduce the temporal asymmetry of the dipolar strength of the field observed during polarity reversals. This behavior arises due to the existence of two parts of the model that are energetically unbalanced, imposing a preferred direction of energy transfer, and we propose that the same mechanism would be the cause of the temporal asymmetry of the geodynamo. We present a simple model for the axial dipole moment (ADM) of the geomagnetic field based on a stochastic differential equation for two coupled particles in a biquadratic potential, subjected to Gaussian random perturbations. This model generates aperiodic reversals and excursions separated by stable polarity periods. The model reproduces the temporal asymmetry of geomagnetic reversals, with slower decaying rates before the reversal and faster growing rates after it. This temporal asymmetry is possible because our model is out of equilibrium. The existence of a thermal imbalance between the two particles sets a preferential sense for the energy flux and renders the process irreversible.