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Varying the forcing...
Varying the forcing scale in low Prandtl number dynamos
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- Brandenburg, Axel, 1959- (author)
- Stockholms universitet,KTH,Nordic Institute for Theoretical Physics NORDITA,Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.;Stockholm Univ, SE-10691 Stockholm, Sweden.;Univ Colorado, JILA, Boulder, CO 80303 USA.;Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80303 USA.;Stockholm Univ, Dept Astron, SE-10691 Stockholm, Sweden.,Nordiska institutet för teoretisk fysik (Nordita),Institutionen för astronomi,University of Colorado, USA
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- Haugen, N. E. L. (author)
- SINTEF Energy Res, N-7465 Trondheim, Norway.;NTNU, Dept Energy & Proc Engn, N-7491 Trondheim, Norway.
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- Li, Xiang-Yu (author)
- Stockholms universitet,Nordiska institutet för teoretisk fysik (Nordita),Meteorologiska institutionen (MISU),University of Colorado, USA,Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA.;Stockholm Univ, SE-10691 Stockholm, Sweden.;Stockholm Univ, Dept Meteorol, Stockholm, Sweden.;Stockholm Univ, Bolin Ctr Climate Res, Stockholm, Sweden.;Nordita SU
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- Subramanian, K. (author)
- Inter Univ Ctr Astron & Astrophys, Post Bag 4,Pune Univ Campus, Pune 411007, Maharashtra, India.
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(creator_code:org_t)
- 2018-06-14
- 2018
- English.
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In: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 479:2, s. 2827-2833
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Abstract
Subject headings
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- Small-scale dynamos are expected to operate in all astrophysical fluids that are turbulent and electrically conducting, for example the interstellar medium, stellar interiors, and accretion discs, where theymay also be affected by or competing with large-scale dynamos. However, the possibility of small-scale dynamos being excited at small and intermediate ratios of viscosity to magnetic diffusivity (the magnetic Prandtl number) has been debated, and the possibility of them depending on the large-scale forcing wavenumber has been raised. Here, we show, using four values of the forcing wavenumber, that the small-scale dynamo does not depend on the scale separation between the size of the simulation domain and the integral scale of the turbulence, i.e. the forcing scale. Moreover, the spectral bottleneck in turbulence, which has been implied as being responsible for raising the excitation conditions of small-scale dynamos, is found to be invariant under changing the forcing wavenumber. However, when forcing at the lowest few wavenumbers, the effective forcing wavenumber that enters in the definition of the magnetic Reynolds number is found to be about twice the minimum wavenumber of the domain. Our work is relevant to future studies of small-scale dynamos, of which several applications are being discussed.
Subject headings
- NATURVETENSKAP -- Fysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences (hsv//eng)
Keyword
- dynamo
- magnetic fields
- MHD
- turbulence
- Sun: dynamo
Publication and Content Type
- ref (subject category)
- art (subject category)
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