Issue A&A Volume 404, Number 2, June III 2003 Page(s) 701 - 707 Section Diffuse matter in space DOI http://dx.doi.org/10.1051/0004-6361:20030580

A&A 404, 701-707 (2003)
DOI: 10.1051/0004-6361:20030580

Solitary waves in a Hall solar wind plasma

I. Ballai^{1, 2}, J. C. Thelen² and B. Roberts<sup>2

1</sup>  Space and Atmosphere Research Center (SPARC), Department of Applied Mathematics, University of Sheffield, Hounsfield Road, Hicks Building, Sheffield S3 7RH, UK
²  School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife, KY16 9SS, Scotland, UK

(Received 2 April 2002 / Accepted 14 April 2003)

Abstract
In the solar wind, the effect of the Hall current generated perpendicular to the ambient magnetic field can influence the plasma behaviour. In particular, the Hall current introduces wave dispersion which may compensate the nonlinear steepening of waves. In the presence of viscosity, these effects lead to a slowly decaying KdV soliton. Here we investigate a solitary wave propagating obliquely to an ambient magnetic field. Our results show that the nonlinear slow magnetoacoustic wave, that arises from nonlinear steepening, propagates faster than the linear slow mode speed; by contrast, the nonlinear fast magnetoacoustic wave propagates slower than the linear fast wave speed. We apply our calculations to the observed non-thermal Doppler broadening of the ion emission line, measured by the SoHO UVCS telescope in the acceleration region of the solar wind. The observed line broadening is recovered in our theory by the nonlinear slow magnetoacoustic waves; by contrast, fast magnetoacoustic produce too narrow broadening.

Key words: magnetohydrodynamics (MHD) -- Sun: solar wind -- waves

Offprint request: I. Ballai, i.ballai@sheffield.ac.uk

© ESO 2003

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