Abstract Fluctuations in the paleomagnetic field suggest that dipole decay time is shorter than expected, based on current estimates for molecular magnetic diffusivity outer core. Similar behavior observed turbulent dynamo simulations, where short cannot be attributed to higher‐order modes. We interpret as a signature of diffusion and show mean‐field theory can quantitatively account results. The predictions depend amplitude length scale flow interacts with field. rely pairwise balance...

Planetary magnetic fields are generated by the motion of conductive fluid in planet's interior. Complex flows not required for dynamo action; simple have been shown to act as efficient kinematic dynamos, whose physical characteristics more straightforward study. Recently, Chen et al . (2018, J. Fluid Mech. 839 , 1–32. ( doi:10.1017/jfm.2017.924 )) found optimal, unconstrained a sphere, which, despite being theoretical importance, is limited practical use. We extend their work restricting...

Abstract Studies of the Earth's secular variation have blossomed in recent decades, due to availability brand‐new satellite data. In particular, flow inversions at core surface that incorporate effects rapid rotation a priori been able provide new insight into flows with time scales as short few years. These models mostly developed cylindrical representation, while inversion methods are based on spherical representation flow. This technical brief links band‐limited expressions for...

Abstract Variations in the geomagnetic field occur on a vast range of time scales, from milliseconds to millions years. The advent satellite measurements has allowed for detailed studies short timescale behaviour, but understanding its long evolution remains challenging due sparsity paleomagnetic record. This paper introduces theory framework studying magnetic generation as result stochastic fluid motions. Starting kinematic dynamo model (the Kazantsev model), we derive statistical...

<p>An ever-expanding catalogue of satellite data has laid the foundations for new studies Earth’s secular variation and acceleration. Studies that encode a-priori axial rigidity conferred to core flows by rapid rotation have revealed novel fast dynamics improved estimates magnetic field strength inside core. Within this context, a formalism christened “plesio-geostrophy” (PG) was developed Jackson Maffei (<em>Proc. Roy....

Variations in the geomagnetic field occur on a vast range of time scales, from milliseconds to millions years. The advent satellite measurements has allowed for detailed studies short timescale behaviour, but understanding long evolution remains challenging due sparsity paleomagnetic record. This paper introduces theory framework studying magnetic generation as result stochastic fluid motions. By constructing kinematic dynamo model, we derive statistical properties that may be compared...