Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...313..448z&link_type=abstract
Astronomy and Astrophysics, v.313, p.448-456
Astronomy and Astrophysics
Astrophysics
6
Magnetohydrodynamics, Ism: General, Supernova Remnants, Magnetic Fields, Turbulence
Scientific paper
Numerical simulations of supernova remnants are used to explore the nonlinear aspects of magnetic quenching in α{OMEGA}-dynamos. The feedback of the magnetic field on the turbulence is taken into account by solving the selfconsistent 3-dimensional magnetohydrodynamical problem. The quenched α-coefficients α_yy_, α_yx_, and α_zz_ are derived from the given velocity field and magnetic field of a single explosion for the realistic situation of a vertically stratified ensemble of supernovae in galactic discs. A different quenching behavior is found for the different α-components. α_yy_ and α_zz_ are strongly suppressed by magnetic fields which results in a reduction of their amplitudes. In contrast, α_yx_ depends only slightly on the mean magnetic field. A detailed comparison with analytic results based on the second-order correlation approximation of mean-field magnetohydrodynamics shows a surprisingly good agreement for the magnetic α_yy_-quenching. However, the correlation approximation does not provide a good description of the quenching behavior for the remaining components. For the magnetic quenching of α_zz_ and α_yx_, heuristic quenching functions are postulated which fit the numerical data within a few per cent error. These expressions can be used in future dynamo models taking into account the quenching phenomenon more accurately than is presently possible.
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