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Astrophysical significance of the anisotropic kinetic alpha effect

Lookup NU author(s): Professor Axel Brandenburg


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The generation of large scale flows by the anisotropic kinetic alpha (AKA) effect is investigated in simulations with a suitable time-dependent space- and time-periodic anisotropic forcing lacking parity invariance. The forcing pattern moves relative to the fluid, which leads to a breaking of the Galilean invariance as required for the AKA effect to exist. The AKA effect is found to produce a clear large scale flow pattern when the Reynolds number, R, is small as only a few modes are excited in linear theory. In this case the non-vanishing components of the AKA tensor are dynamically independent of the Reynolds number. For larger values of R, many more modes are excited and the components of the AKA tensor are found to decrease rapidly with increasing value of R. However, once there is a magnetic field (imposed and of sufficient strength, or dynamo-generated and saturated) the field begins to suppress the AKA effect, regardless of the value of R. It is argued that the AKA effect is unlikely to be astrophysically significant unless the magnetic field is weak and R is small.

Publication metadata

Author(s): Brandenburg A, Rekowski BV

Publication type: Article

Publication status: Published

Journal: Astronomy and Astrophysics

Year: 2001

Volume: 379

Issue: 3

Pages: 1153-1160

ISSN (print): 0004-6361

ISSN (electronic): 1432-0746

Publisher: EDP Sciences


DOI: 10.1051/0004-6361:20011400


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