*Astron. Astrophys. 330, 726-738 (1998)*
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## Numerical simulations of impulsively generated MHD waves
in a potential coronal arcade
**
R. Oliver ,
K. Murawski
**^{*} and
J.L. Ballester
Departament de
Fsica, Universitat de les
Illes Balears, E-07071 Palma de Mallorca, Spain
*Received 1 October 1996 / Accepted 12 September 1997*
**Abstract**
Impulsively generated waves in coronal arcades are simulated
numerically by an application of nonlinear ideal magnetohydrodynamic
(MHD) equations. The simulations are performed in the
-plane on a non-uniform Cartesian mesh. In this
geometry the magnetic field can be expressed in terms of the vector
potential. The governing equations, which are applied in the limit of
low plasma- , are solved by a flux corrected
transport method. The model excludes the Alfvén waves and,
since the slow mode is absent in the cold plasma limit, the excited
disturbances are fast magnetosonic waves.
Numerical results show that for short times after the impulse is
launched (i. e., in the linear regime), only motions normal to the
equilibrium magnetic field get propagated away from the position of
the initial displacement and that any velocity parallel to the
unperturbed magnetic field lines remains essentially unchanged in
time. In the nonlinear regime there is conversion between normal and
parallel flow and the two velocity components propagate from the site
of the initial impulse. In addition, nonlinearities that are built in
the MHD equations modify the shape and speed of the propagating
wavefront, an effect that becomes most noticeable where the wave
amplitude is larger. The effect of nonlinearity on down-going
perturbations is to speed up positive wave amplitudes and to slow down
negative wave amplitudes (positive and negative refers to the sign of
the normal velocity component). On the contrary, up-going positive and
negative waves are slowed down and speeded up, respectively.
Impulsively generated waves exhibit temporal signatures with
characteristic time scales of the order of 10 s. Similar scales have
been recently reported in radio observations, microwaves, and hard
X-rays.
**Key words:** Sun:
corona
Sun: magnetic
fields
MHD
* Permanent address: Division of Environmental Studies, Technical University of Lublin, ul. Nadbystrzycka 40, 20-618 Lublin, Poland
*Send offprint requests to:* J.L. Ballester
© European Southern Observatory (ESO) 1998
Online publication: January 16, 1998
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