New scaling for the alpha effect in slowly rotating turbulence

A. Brandenburg, O. Gressel, P. J. Käpylä, N. Kleeorin, M. J. Mantere, I. Rogachevskii

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19 Scopus citations


Using simulations of slowly rotating stratified turbulence, we show that the α 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 α 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.

Original languageEnglish
Article number127
JournalAstrophysical Journal
Issue number2
StatePublished - 10 Jan 2013


  • Sun: dynamo
  • magnetohydrodynamics (MHD)
  • turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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