Rapidly rotating spherical Couette flow in a dipolar magnetic field: an experimental study of the mean axisymmetric flow

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dc.creatorNataf, Henri-Claude
dc.creatorAlboussiere, Thierry
dc.creatorBrito, Daniel
dc.creatorCardin, Philippe
dc.creatorGagnière, Nadège
dc.creatorJault, Dominique
dc.creatorSchmitt, Denys
dc.date2007-05-10
dc.date2008-08-08
dc.date.accessioned2026-07-07T10:17:48Z
dc.date.available2026-07-07T10:17:48Z
dc.descriptionIn order to explore the magnetostrophic regime expected for planetary cores, experiments have been conducted in a rotating sphere filled with liquid sodium, with an imposed dipolar magnetic field (the DTS setup). The field is produced by a permanent magnet enclosed in an inner sphere, which can rotate at a separate rate, producing a spherical Couette flow. The flow properties are investigated by measuring electric potentials on the outer sphere, the induced magnetic field in the laboratory frame, and velocity profiles inside the liquid sodium using ultrasonic Doppler velocimetry. The present article focuses on the time-averaged axisymmetric part of the flow. The Doppler profiles show that the angular velocity of the fluid is relatively uniform in most of the fluid shell, but rises near the inner sphere, revealing the presence of a magnetic wind, and gently drops towards the outer sphere. The transition from a magnetostrophic flow near the inner sphere to a geostrophic flow near the outer sphere is controlled by the local Elsasser number. For Rossby numbers up to order 1, the observed velocity profiles all show a similar shape. Numerical simulations in the linear regime are computed, and synthetic velocity profiles are compared with the measured ones. In the geostrophic region, a torque-balance model provides very good predictions. We find that the induced magnetic field varies in a consistent fashion, and displays a peculiar peak in the counter-rotating regime. This happens when the fluid rotation rate is almost equal and opposite to the outer sphere rotation rate. The fluid is then almost at rest in the laboratory frame, and the Proudman-Taylor constraint vanishes, enabling a strong meridional flow. We suggest that dynamo action might be favored in such a situation.
dc.descriptionin press in Physics of the Earth and Planetary Interiors
dc.identifierhttps://arxiv.org/abs/0705.1412
dc.identifierhttp://arxiv.org/abs/0705.1412
dc.identifierPhysics of The Earth and Planetary Interiors 170 (2008) 60-72
dc.identifierdoi:10.1016/j.pepi.2008.07.034
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/173979
dc.subjectGeophysics
dc.subjectAstrophysics
dc.subjectFluid Dynamics
dc.titleRapidly rotating spherical Couette flow in a dipolar magnetic field: an experimental study of the mean axisymmetric flow
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