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Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, article id A51Article in journal (Refereed) Published
Abstract [en]

Aims. We investigate dynamo action in global compressible solar-like convective dynamos in the framework of mean-field theory. Methods. We simulate a solar-type star in a wedge-shaped spherical shell, where the interplay between convection and rotation self-consistently drives a large-scale dynamo. To analyze the dynamo mechanism we apply the test-field method for azimuthally (φ) averaged fields to determine the 27 turbulent transport coefficients of the electromotive force, of which six are related to the α tensor. This method has previously been used either in simulations in Cartesian coordinates or in the geodynamo context and is applied here for the first time to fully compressible simulations of solar-like dynamos. Results. We find that the φφ-component of the α tensor does not follow the profile expected from that of kinetic helicity. The turbulent pumping velocities significantly alter the effective mean flows acting on the magnetic field and therefore challenge the flux transport dynamo concept. All coefficients are significantly affected by dynamically important magnetic fields. Quenching as well as enhancement are being observed. This leads to a modulation of the coefficients with the activity cycle. The temporal variations are found to be comparable to the time-averaged values and seem to be responsible for a nonlinear feedback on the magnetic field generation. Furthermore, we quantify the validity of the Parker-Yoshimura rule for the equatorward propagation of the mean magnetic field in the present case.

Place, publisher, year, edition, pages
EDP Sciences, 2018. Vol. 609, article id A51
Keywords [en]
Dynamo, Magnetohydrodynamics (MHD), Sun: activity, Sun: magnetic fields, Sun: rotation, Turbulence
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-221693DOI: 10.1051/0004-6361/201628136ISI: 000419994200019Scopus ID: 2-s2.0-85040311634OAI: oai:DiVA.org:kth-221693DiVA, id: diva2:1176399
Funder
Swedish Research Council, 621-2011-5076 2012-5797EU, FP7, Seventh Framework Programme, 623609
Note

QC 20180122

Available from: 2018-01-22 Created: 2018-01-22 Last updated: 2018-01-29Bibliographically approved

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Nordic Institute for Theoretical Physics NORDITA
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