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Title:
Large-scale Dynamos in Rigidly Rotating Turbulent Convection
Authors:
Käpylä, Petri J.; Korpi, Maarit J.; Brandenburg, Axel
Affiliation:
AA(Observatory, University of Helsinki, P.O. Box 14, FI-00014 University of Helsinki, Helsinki, Finland ), AB(Observatory, University of Helsinki, P.O. Box 14, FI-00014 University of Helsinki, Helsinki, Finland), AC(NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden)
Publication:
The Astrophysical Journal, Volume 697, Issue 2, pp. 1153-1163 (2009). (ApJ Homepage)
Publication Date:
06/2009
Origin:
IOP
Astronomy Keywords:
convection, MHD, stars: magnetic fields, Sun: magnetic fields, turbulence
DOI:
10.1088/0004-637X/697/2/1153
Bibliographic Code:
2009ApJ...697.1153K

Abstract

The existence of large-scale dynamos in rigidly rotating turbulent convection without shear is studied using three-dimensional numerical simulations of penetrative rotating compressible convection. We demonstrate that rotating convection in a Cartesian domain can drive a large-scale dynamo even in the absence of shear. The large-scale field contains a significant fraction of the total field in the saturated state. The simulation results are compared with one-dimensional mean-field dynamo models where turbulent transport coefficients, as determined using the test field method, are used. The reason for the absence of large-scale dynamo action in earlier studies is shown to be due to the rotation being too slow: whereas the α-effect can change sign, its magnitude stays approximately constant as a function of rotation, and the turbulent diffusivity decreases monotonically with increasing rotation. Only when rotation is rapid enough a large-scale dynamo can be excited. The one-dimensional mean-field model with dynamo coefficients from the test-field results predicts reasonably well the dynamo excitation in the direct simulations. This result further validates the test field procedure and reinforces the interpretation that the observed dynamo is driven by a turbulent α-effect. This result demonstrates the existence of an α-effect and an α2-dynamo with natural forcing.
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