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Magnetic Helicity Fluxes in Dynamos from Rotating Inhomogeneous Turbulence
Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Faculty of Science, Department of Physics. Carnegie Mellon University, USA; Ilia State University, Georgia.ORCID iD: 0000-0002-7304-021X
Number of Authors: 22025 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 984, no 1, article id 78Article in journal (Refereed) Published
Abstract [en]

We analyze direct numerical simulations of large-scale dynamos in inhomogeneous nonhelically driven rotating turbulence with and without shear. The forcing is modulated so that the turbulent intensity peaks in the middle of the computational domain and drops to nearly zero at the two ends above and below the midplane. A large-scale dynamo is driven by an α effect of opposite signs in the two hemispheres. In the presence of shear, the hemispheric magnetic helicity flux from small-scale fields becomes important and can even overcompensate for the magnetic helicity transferred by the α effect between large and small scales. This effect has not previously been observed in nonshearing simulations. Our numerical simulations show that the hemispheric magnetic helicity fluxes are nearly independent of the magnetic Reynolds number, but those between large and small scales, and the consequent dynamo effect, are still found to decrease with increasing Reynolds number—just like in nonshearing dynamos. However, in contrast to nonshearing dynamos, where the generated mean magnetic field declines with increasing magnetic Reynolds number, it is now found to remain independent of it. This suggests that catastrophic dynamo quenching is alleviated by the shear-induced hemispheric small-scale magnetic helicity fluxes that can even overcompensate the fluxes between large and small scales and thereby cause resistive contributions.

Place, publisher, year, edition, pages
2025. Vol. 984, no 1, article id 78
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-243354DOI: 10.3847/1538-4357/adc561ISI: 001478789200001Scopus ID: 2-s2.0-105003981222OAI: oai:DiVA.org:su-243354DiVA, id: diva2:1960163
Available from: 2025-05-22 Created: 2025-05-22 Last updated: 2025-05-22Bibliographically approved

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Brandenburg, Axel

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Nordic Institute for Theoretical Physics (Nordita)Department of AstronomyThe Oskar Klein Centre for Cosmo Particle Physics (OKC)Department of Physics
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