Large-scale-vortex dynamos in planar rotating convection
| Autor: | Céline Guervilly, David W. Hughes, Chris A. Jones |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Convection
FOS: Physical sciences Magnetic Reynolds number 01 natural sciences 010305 fluids & plasmas Physics::Fluid Dynamics Physics - Geophysics symbols.namesake 0103 physical sciences 010306 general physics Solar and Stellar Astrophysics (astro-ph.SR) Earth and Planetary Astrophysics (astro-ph.EP) Physics Magnetic energy Mechanical Engineering Fluid Dynamics (physics.flu-dyn) Reynolds number Physics - Fluid Dynamics Mechanics Condensed Matter Physics Geophysics (physics.geo-ph) Magnetic field Vortex Astrophysics - Solar and Stellar Astrophysics Mechanics of Materials Dynamo theory symbols Astrophysics - Earth and Planetary Astrophysics Dynamo |
| Zdroj: | Journal of Fluid Mechanics. 815:333-360 |
| ISSN: | 1469-7645 0022-1120 |
| Popis: | Several recent studies have demonstrated how large-scale vortices may arise spontaneously in rotating planar convection. Here we examine the dynamo properties of such flows in rotating Boussinesq convection. For moderate values of the magnetic Reynolds number ($100 \lesssim Rm \lesssim 550$, with $Rm$ based on the box depth and the convective velocity), a large-scale (i.e. system-size) magnetic field is generated. The amplitude of the magnetic energy oscillates in time, nearly out of phase with the oscillating amplitude of the large-scale vortex. The large-scale vortex is disrupted once the magnetic field reaches a critical strength, showing that these oscillations are of magnetic origin. The dynamo mechanism relies on those components of the flow that have length scales lying between that of the large-scale vortex and the typical convective cell size; smaller-scale flows are not required. The large-scale vortex plays a crucial role in the magnetic induction despite being essentially two-dimensional; we thus refer to this dynamo as a large-scale-vortex dynamo. For larger magnetic Reynolds numbers, the dynamo is small scale, with a magnetic energy spectrum that peaks at the scale of the convective cells. In this case, the small-scale magnetic field continuously suppresses the large-scale vortex by disrupting the correlations between the convective velocities that allow it to form. The suppression of the large-scale vortex at high $Rm$ therefore probably limits the relevance of the large-scale-vortex dynamo to astrophysical objects with moderate values of $Rm$, such as planets. In this context, the ability of the large-scale-vortex dynamo to operate at low magnetic Prandtl numbers is of great interest. 28 pages, 17 figures, accepted for publication in J. Fluid Mech |
| Databáze: | OpenAIRE |
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