EDP Sciences
Free access
Volume 435, Number 1, May III 2005
Page(s) 313 - 325
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20042361

A&A 435, 313-325 (2005)
DOI: 10.1051/0004-6361:20042361

MHD wave propagation in the neighbourhood of two null points

J. A. McLaughlin and A. W. Hood

School of Mathematics and Statistics, University of St Andrews, KY16 9SS, UK
    e-mail: james@mcs.st-and.ac.uk

(Received 12 November 2004 / Accepted 24 January 2005)

The nature of fast magnetoacoustic and Alfvén waves is investigated in a zero $\beta$ plasma in the neighbourhood of a pair of two-dimensional null points. This gives an indication of wave propagation in the low $\beta$ solar corona, for a more complicated magnetic configuration than that looked at by McLaughlin & Hood (2004, A&A, 420, 1129). It is found that the fast wave is attracted to the null points and that the front of the wave slows down as it approaches the null point pair. Here, the wave splits and part of the wave accumulates at one null and the rest at the other. Current density will then accumulate at these points and ohmic dissipation will then extract the energy in the wave at these points. This suggests locations where wave heating will occur in the corona. The Alfvén wave behaves in a different manner in that the wave accumulates along the separatrices. Hence, the current density will accumulate at this part of the topology and this is where wave heating will occur. However, the phenomenon of wave accumulation at a specific place is a feature of both wave types, and illustrates the importance of studying the topology of the corona when considering MHD wave propagation.

Key words: magnetohydrodynamics (MHD) -- waves -- Sun: corona

© ESO 2005