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Magnetic Helicity Fluxes in Dynamos from Rotating Inhomogeneous Turbulence
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, Stockholm, SE-10691, Sweden; McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, 15213, PA, United States; School of Natural Sciences and Medicine, Ilia State University, 3-5 Cholokashvili Avenue, Tbilisi, 0194, Georgia.ORCID iD: 0000-0002-7304-021X
Physics and Astronomy Department, Johns Hopkins University, Baltimore, 21218, MD, United States.
2025 (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 alpha 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 alpha 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
American Astronomical Society , 2025. Vol. 984, no 1, article id 78
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-364535DOI: 10.3847/1538-4357/adc561ISI: 001478789200001Scopus ID: 2-s2.0-105003981222OAI: oai:DiVA.org:kth-364535DiVA, id: diva2:1972564
Note

QC 20250618

Available from: 2025-06-18 Created: 2025-06-18 Last updated: 2025-06-18Bibliographically approved

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Brandenburg, Axel

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