Solenoidal force balances in numerical dynamos

Numerical simulations of the geodynamo (and other planetary dynamos) have made significant progress in recent years. As computing power has advanced, some new models claim to be ever more appropriate for understanding Earth's core dynamics. One measure of the success of such models is the abili...

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Bibliographic Details
Published inJournal of fluid mechanics Vol. 964
Main Authors Teed, Robert J., Dormy, Emmanuel
Format Journal Article
LanguageEnglish
Published Cambridge, UK Cambridge University Press 01.06.2023
Cambridge University Press (CUP)
Subjects
Dynamics
Dynamo theory
Earth core
Fluid flow
Fluid mechanics
Geophysics
Incompressible flow
JFM Papers
Lorentz force
Mathematical models
Mathematical Physics
Mathematics
Mechanics
Microbalances
Nonlinear Sciences
Partial differential equations
Physics
Pressure gradients
Rayleigh number
Reynolds number
Rotating generators
Simulation
Viscosity
quasi-geostrophic flows
dynamo theory
geodynamo
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Summary:Numerical simulations of the geodynamo (and other planetary dynamos) have made significant progress in recent years. As computing power has advanced, some new models claim to be ever more appropriate for understanding Earth's core dynamics. One measure of the success of such models is the ability to replicate the expected balance between forces operating within the core; Coriolis and Lorentz forces are predicted to be most important. The picture is complicated for an incompressible flow by the existence of the pressure gradient force which renders the gradient parts of all other forces dynamically unimportant. This can confuse the situation, especially when the scale dependence of forces is considered. In this work we investigate force balances through the alternative approach of eliminating gradient parts of each force to form ‘solenoidal force balances’. We perform a length-scale-dependent analysis for several spherical simulations and find that removal of gradient parts offers an alternative picture of the force balance compared with looking at traditional forces alone. Solenoidal force balances provide some agreement with the results of previous studies but also significant differences. They offer a cleaner overall picture of the dynamics and introduce differences at smaller scales. This has implications for geodynamo models purporting to have reached Earth-like regimes: in order to achieve a meaningful comparison of forces, only the solenoidal part of forces should be considered.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.332