Effects of enhanced stratification on equatorward dynamo wave propagation

Petri J. Käpylä, Maarit Mantere, Elizabeth Cole, Jörn Warnecke, Axel Brandenburg

    Research output: Contribution to journalArticleScientificpeer-review

    59 Citations (Scopus)

    Abstract

    We present results from simulations of rotating magnetized turbulent convection in spherical wedge geometry representing parts of the latitudinal and longitudinal extents of a star. Here we consider a set of runs for which the density stratification is varied, keeping the Reynolds and Coriolis numbers at similar values. In the case of weak stratification, we find quasi-steady dynamo solutions for moderate rotation and oscillatory ones with poleward migration of activity belts for more rapid rotation. For stronger stratification, the growth rate tends to become smaller. Furthermore, a transition from quasi-steady to oscillatory dynamos is found as the Coriolis number is increased, but now there is an equatorward migrating branch near the equator. The breakpoint where this happens corresponds to a rotation rate that is about three to seven times the solar value. The phase relation of the magnetic field is such that the toroidal field lags behind the radial field by about π/2, which can be explained by an oscillatory α2 dynamo caused by the sign change of the α-effect about the equator. We test the domain size dependence of our results for a rapidly rotating run with equatorward migration by varying the longitudinal extent of our wedge. The energy of the axisymmetric mean magnetic field decreases as the domain size increases and we find that an m = 1 mode is excited for a full 2π azimuthal extent, reminiscent of the field configurations deduced from observations of rapidly rotating late-type stars.

    Original languageEnglish
    Article number41
    JournalAstrophysical Journal
    Volume778
    Issue number1
    DOIs
    Publication statusPublished - 20 Nov 2013
    MoE publication typeA1 Journal article-refereed

    Keywords

    • convection
    • dynamo
    • magnetohydrodynamics (MHD)
    • Sun: activity
    • Sun: rotation
    • turbulence

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