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Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
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2013 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 762, no 2, 127Article in journal (Refereed) Published
Abstract [en]

Using simulations of slowly rotating stratified turbulence, we show that the alpha effect responsible for the generation of astrophysical magnetic fields is proportional to the logarithmic gradient of kinetic energy density rather than that of momentum, as was previously thought. This result is in agreement with a new analytic theory developed in this paper for large Reynolds numbers and slow rotation. Thus, the contribution of density stratification is less important than that of turbulent velocity. The a effect and other turbulent transport coefficients are determined by means of the test-field method. In addition to forced turbulence, we also investigate supernova-driven turbulence and stellar convection. In some cases (intermediate rotation rate for forced turbulence, convection with intermediate temperature stratification, and supernova-driven turbulence), we find that the contribution of density stratification might be even less important than suggested by the analytic theory.

Place, publisher, year, edition, pages
2013. Vol. 762, no 2, 127
Keyword [en]
magnetohydrodynamics (MHD), Sun: dynamo, turbulence
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:su:diva-87695DOI: 10.1088/0004-637X/762/2/127ISI: 000313008900061OAI: diva2:605850
EU, European Research Council, 227915


Available from: 2013-02-15 Created: 2013-02-14 Last updated: 2016-07-01Bibliographically approved

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Brandenburg, Axel
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Department of AstronomyNordic Institute for Theoretical Physics (Nordita)
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