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Lagrangian Coherent Structures in Nonlinear Dynamos

Rempel, E. L. and Chian, A. C.- L. and Brandenburg, A. (2011) Lagrangian Coherent Structures in Nonlinear Dynamos. Astrophysical Journal Letters, 735 (1). Art. No. L9. ISSN 2041-8205.

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Turbulence and chaos play a fundamental role in stellar convective zones through the transport of particles, energy, and momentum, and in fast dynamos, through the stretching, twisting, and folding of magnetic flux tubes. A particularly revealing way to describe turbulent motions is through the analysis of Lagrangian coherent structures (LCSs), which are material lines or surfaces that act as transport barriers in the fluid. We report the detection of LCSs in helical MHD dynamo simulations with scale separation. In an Arnold-Beltrami-Childress flow, two dynamo regimes, a propagating coherent mean-field regime and an intermittent regime, are identified as the magnetic diffusivity is varied. The sharp contrast between the chaotic tangle of attracting and repelling LCSs in both regimes permits a unique analysis of the impact of the magnetic field on the velocity field. In a second example, LCSs reveal the link between the level of chaotic mixing of the velocity field and the saturation of a large-scale dynamo when the magnetic field exceeds the equipartition value.

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Additional Information:© 2011 The American Astronomical Society. Received 2010 November 23; accepted 2011 May 2; published 2011 June 6. E.L.R. thanks the University of Cambridge (DAMTP) for the hospitality and Professor Michael Proctor for valuable discussions. E.L.R. and A.C.L.C. acknowledge the support by CNPq (Brazil) and FAPESP (Brazil). A.C.L.C. acknowledges the award of a Guggenheim Fellowship and the hospitality of Caltech.
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Guggenheim FellowshipUNSPECIFIED
Subject Keywords:chaos; dynamo; magnetohydrodynamics (MHD)
Issue or Number:1
Classification Code:PACS: 97.10.Cv; 97.10.Ld; 95.30.Qd
Record Number:CaltechAUTHORS:20110816-104035079
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Official Citation:Lagrangian Coherent Structures in Nonlinear Dynamos E. L. Rempel, A. C.-L. Chian and A. Brandenburg doi: 10.1088/2041-8205/735/1/L9
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24884
Deposited By: Ruth Sustaita
Deposited On:16 Aug 2011 17:54
Last Modified:03 Oct 2019 03:00

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