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HYSTERESIS BETWEEN DISTINCT MODES OF TURBULENT DYNAMOS
Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).ORCID-id: 0000-0002-8883-3562
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).ORCID-id: 0000-0002-7304-021X
Antal upphovsmän: 32015 (Engelska)Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 803, nr 2, artikel-id 95Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Nonlinear mean-field models of the solar dynamo show long-term variability, which may be relevant to different states of activity inferred from long-term radiocarbon data. This paper is aimed at probing the dynamo hysteresis predicted by the recent mean-field models of Kitchatinov & Olemskoy with direct numerical simulations. We perform three-dimensional (3D) simulations of large-scale dynamos in a shearing box with helically forced turbulence. As an initial condition, we either take a weak random magnetic field or we start from a snapshot of an earlier simulation. Two quasi-stable states are found to coexist in a certain range of parameters close to the onset of the large-scale dynamo. The simulations converge to one of these states depending on the initial conditions. When either the fractional helicity or the magnetic Prandtl number is increased between successive runs above the critical value for onset of the dynamo, the field strength jumps to a finite value. However, when the fractional helicity or the magnetic Prandtl number is then decreased again, the field strength stays at a similar value (strong field branch) even below the original onset. We also observe intermittent decaying phases away from the strong field branch close to the point where large-scale dynamo action is just possible. The dynamo hysteresis seen previously in mean-field models is thus reproduced by 3D simulations. Its possible relation to distinct modes of solar activity such as grand minima is discussed.

Ort, förlag, år, upplaga, sidor
2015. Vol. 803, nr 2, artikel-id 95
Nyckelord [en]
dynamo, magnetohydrodynamics (MHD), Sun: activity, Sun: magnetic fields, turbulence
Nationell ämneskategori
Astronomi, astrofysik och kosmologi
Identifikatorer
URN: urn:nbn:se:su:diva-117727DOI: 10.1088/0004-637X/803/2/95ISI: 000353524500047OAI: oai:DiVA.org:su-117727DiVA, id: diva2:819146
Tillgänglig från: 2015-06-10 Skapad: 2015-06-01 Senast uppdaterad: 2022-02-23Bibliografiskt granskad

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Karak, Bidya BinayBrandenburg, Axel

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Nordiska institutet för teoretisk fysik (Nordita)Institutionen för astronomi
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