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Title:
The role of the Yoshizawa effect in the Archontis dynamo
Authors:
Sur, Sharanya; Brandenburg, Axel
Affiliation:
AA(Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411 007, India), AB(NORDITA, AlbaNova University Center, Roslagstullsbacken 23, SE 10691 Stockholm, Sweden; Department of Astronomy, AlbaNova University Center, Stockholm University, SE 10691 Stockholm, Sweden)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 399, Issue 1, pp. 273-280. (MNRAS Homepage)
Publication Date:
10/2009
Origin:
MNRAS
Astronomy Keywords:
magnetic fields , MHD , hydrodynamics , turbulence
DOI:
10.1111/j.1365-2966.2009.15254.x
Bibliographic Code:
2009MNRAS.399..273S

Abstract

The generation of mean magnetic fields is studied for a simple non-helical flow where a net cross-helicity of either sign can emerge. This flow, which is also known as the Archontis flow, is a generalization of the Arnold-Beltrami-Childress flow, but with the cosine terms omitted. The presence of cross-helicity leads to a mean-field dynamo effect that is known as the Yoshizawa effect. Direct numerical simulations of such flows demonstrate the presence of magnetic fields on scales larger than the scale of the flow. Contrary to earlier expectations, the Yoshizawa effect is found to be proportional to the mean magnetic field and can therefore lead to its exponential instead of just linear amplification for magnetic Reynolds numbers that exceed a certain critical value. Unlike α effect dynamos, it is found that the Yoshizawa effect is not notably constrained by the presence of a conservation law. It is argued that this is due to the presence of a forcing term in the momentum equation, which leads to a non-zero correlation with the magnetic field. Finally, the application to energy convergence in solar wind turbulence is discussed.
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