%0 Journal Article
%T Experimental and numerical studies of magnetoconvection in a rapidly rotating spherical shell
%+ Laboratoire de Géophysique Interne et Tectonophysique (LGIT)
%A Gillet, Nicolas
%A Brito, Daniel
%A Jault, Dominique
%A Nataf, Henri-Claude
%< avec comité de lecture
%@ 0022-1120
%J Journal of Fluid Mechanics
%I Cambridge University Press (CUP)
%V 580
%P 123-143
%8 2007
%D 2007
%R 10.1017/S0022112007005289Journal articles
%X Thermal magnetoconvection in a rapidly rotating spherical shell is investigated numerically and experimentally in electrically conductive liquid gallium (Prandtl number P = 0.025), at Rayleigh numbers R up to around 6 times critical and at Ekman numbers E xs223C 10−6. This work follows up the non-magnetic study of convection presented in a companion paper (Gillet et al. 2007). We study here the addition of a z-invariant toroidal magnetic field to the fluid flow. The experimental measurements of fluid velocities by ultrasonic Doppler velocimetry, together with the quasi-geostrophic numerical simulations incorporating a three-dimensional modelling of the magnetic induction processes, demonstrate a stabilizing effect of the magnetic field in the weak-field case, characterized by an Elsasser number Λ < (E/P)1/3. We find that this is explained by the changes of the critical parameters at the onset of convection as Λ increases. As in the non-magnetic study, strong zonal jets of characteristic length scales ℓβ (Rhines length scale) dominates the fluid dynamics. A new characteristic of the magnetoconvective flow is the elongation of the convective cells in the direction of the imposed magnetic field, introducing a new length scale ℓφ. Combining experimental and numerical results, we derive a scaling law $\overline{U} \,{\sim}\, (\widetilde{U}_s \widetilde{U}_{\phi})^{2/3} \,{\sim}\, \widetilde{U}_s{}^{4/3} (\ell_{\phi}/\ell_{\beta})^{2/3}$ where U is the axisymmetric motion amplitude, Ũs and Ũφ are the non-axisymmetric radial and azimuthal motion amplitudes, respectively.
%G English
%L insu-00198860
%U https://insu.hal.science/insu-00198860
%~ INSU
%~ UNIV-SAVOIE
%~ UGA
%~ CNRS
%~ UNIV-GRENOBLE1
%~ INPG
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%~ INRAE
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%~ UNIV-EIFFEL
%~ IFSTTAR-UNIVEIFFEL