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Article overview
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On the problem of large-scale magnetic field generation in rotating compressible convection | | Benjamin Favier
; Paul J. Bushby
; | | Date: |
28 Feb 2013 | | Abstract: | Mean-field dynamo theory suggests that turbulent convection in a rotating
layer of electrically-conducting fluid produces a significant alpha-effect,
which is one of the key ingredients in any mean-field dynamo model. Provided
that this alpha-effect operates more efficiently than (turbulent) magnetic
diffusion, such a system should be capable of sustaining a large-scale dynamo.
However, in the Boussinesq model that was considered by Cattaneo&Hughes (2006)
the dynamo produced small-scale, intermittent magnetic fields with no
significant large-scale component. In this paper, we consider the compressible
analogue of the rotating convective layer that was considered by
Cattaneo&Hughes (2006). Varying the horizontal scale of the computational
domain, we investigate the dependence of the dynamo upon the rotation rate. Our
simulations indicate that these turbulent compressible flows can drive a
small-scale dynamo but, even when the layer is rotating very rapidly (with a
mid-layer Taylor number of Ta=10^8), we find no evidence for the generation of
a significant large-scale component of the magnetic field on a dynamical
timescale. Like Cattaneo&Hughes(2006), we measure a negligible (time-averaged)
alpha-effect when a uniform horizontal magnetic field is imposed across the
computational domain. Although the total horizontal magnetic flux is a
conserved quantity in these simulations, the (depth-dependent)
horizontally-averaged magnetic field always exhibits strong fluctuations. If
these fluctuations are artificially suppressed within the code, we measure a
significant mean electromotive force that is comparable to that found in
related calculations in which the alpha-effect is measured using the test-field
method, even though we observe no large-scale dynamo action. | | Source: | arXiv, 1302.7243 | | Services: | Forum | Review | PDF | Favorites | |
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