A&A 420, 1129-1140 (2004)
DOI: 10.1051/0004-6361:20035900
MHD wave propagation in the neighbourhood of a two-dimensional null point
J. A. McLaughlin and A. W. HoodSchool of Mathematics and Statistics, University of St Andrews, KY16 9SS, UK
(Received 18 December 2003 / Accepted 12 March 2004)
Abstract
The nature of fast magnetoacoustic and Alfvén waves is investigated in a zero
plasma. This gives an indication of wave propagation in the low
solar corona. It is found
that for a two-dimensional null point, the fast wave is attracted to
that point and the front of the wave slows down as it approaches the null point, causing the current density to accumulate
there and rise rapidly.
Ohmic dissipation will extract the energy in the wave at this
point. This illustrates that null points play an important
role in the rapid dissipation of fast magnetoacoustic waves and suggests the location where wave heating will occur in the
corona. The
Alfvén wave behaves in a different manner in
that the wave energy is dissipated along the separatrices. For Alfvén waves that are decoupled from fast waves, the value
of the plasma
is unimportant. However, the phenomenon of dissipating the majority of the wave energy at a specific place is a feature of
both wave types.
Key words: magnetohydrodynamics (MHD) -- waves -- Sun: corona
Offprint request: J. A. McLaughlin, james@mcs.st-and.ac.uk
© ESO 2004