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Mean shear flows generated by nonlinear resonant Alfvén waves

Clack, C.T.M. and Ballai, I. (2009) Mean shear flows generated by nonlinear resonant Alfvén waves. Physics of Plasmas, 16 (7). Art. No. 072115. ISSN 1070-664X

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Abstract

In the context of resonant absorption, nonlinearity has two different manifestations. The first is the reduction in amplitude of perturbations around the resonant point (wave energy absorption). The second is the generation of mean shear flows outside the dissipative layer surrounding the resonant point. Ruderman et al. [Phys. Plasmas 4, 75 (1997)] studied both these effects at the slow resonance in isotropic plasmas. Clack et al. [Astron. Astrophys. 494, 317 (2009)] investigated nonlinearity at the Alfvén resonance; however, they did not include the generation of mean shear flow. In this present paper, we investigate the mean shear flow, analytically, and study its properties. We find that the flow generated is parallel to the magnetic surfaces and has a characteristic velocity proportional to ϵ1/2, where ϵ is the dimensionless amplitude of perturbations far away from the resonance. This is, qualitatively, similar to the flow generated at the slow resonance. The jumps in the derivatives of the parallel and perpendicular components of mean shear flow across the dissipative layer are derived. We estimate the generated mean shear flow to be of the order of 10 km s−1 in both the solar upper chromosphere and solar corona; however, this value strongly depends on the choice of boundary conditions. It is proposed that the generated mean shear flow can produce a Kelvin–Helmholtz instability at the dissipative layer which can create turbulent motions. This instability would be an additional effect, as a Kelvin–Helmholtz instability may already exist due to the velocity field of the resonant Alfvén waves. This flow can also be superimposed onto existing large scale motions in the solar upper atmosphere.

Item Type: Article
Copyright, Publisher and Additional Information: © 2009 American Institute of Physics. This is an author produced version of a paper published in 'Physics of Plasmas'. Uploaded in accordance with the publisher's self-archiving policy.
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > School of Mathematics and Statistics (Sheffield)
Depositing User: Mrs Megan Hobbs
Date Deposited: 17 Mar 2010 15:40
Last Modified: 05 Jun 2014 02:30
Published Version: http://dx.doi.org/10.1063/1.3194273
Status: Published
Publisher: American Institute of Physics
Refereed: Yes
Identification Number: 10.1063/1.3194273
Related URLs:
URI: http://eprints.whiterose.ac.uk/id/eprint/10663

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