Astronomical Institute, Utrecht Univ., Utrecht, The Netherlands
Department of Atomic Physics, Eötvös Univ., Hungary
accepted by Astronomy & Astrophysics
We present numerical simulations, obtained with the Versatile Advection Code, of the oscillations of an inverse polarity prominence. The internal prominence equilibrium, the surrounding corona and the inert photosphere are well represented. Gravity and thermodynamics are not taken into account, but it is argued that these are not crucial. The oscillations can be understood in terms of a solid body moving through a plasma. The mass of this solid body is determined by the magnetic field topology, not by the prominence mass proper. The model also allows us to study the effect of of the ambient coronal plasma on the motion of the prominence body. Horizontal oscillations are damped through the emission of sound waves while vertical oscillations are damped through the emission of Alfvén waves.
The isothermal MHD equations are solved on a 2.5D non-uniform Cartesian grid with the FCT algorithm. The initial conditions for the arcade and the prominence are obtained by a sophisticated relaxation procedure. Then the stationary prominence is kicked, and the the resulting damped oscillations are calculated by the code. The non-reflecting coronal boundary conditions are achieved by the strongly stretched grid, which places the boundaries far away. It is more difficult to represent the photosphere, which behaves like a solid wall with frozen in field lines that make an angle.