Magnetoacoustic waves in a vertical flare current-sheet in a gravitationally stratified solar atmosphere

¹ University of South Bohemia, Faculty of Science, Institute of Physics and Biophysics, Branišovská 10, 370 05 České Budějovice, Czech Republic
e-mail: pj@matfyz.cz
² Academy of Sciences of the Czech Republic, v. v. i., Astronomical Institute, Fričova 258, 251 65 Ondřejov, Czech Republic
³ Maria Curie-Skłodowska University, Institute of Physics, Group of Astrophysics, Radziszewskiego 10, 20 031 Lublin, Poland

Received: 26 June 2012
Accepted: 9 August 2012

Abstract

Aims. We numerically studied evolution of impulsively generated magnetoacoustic waves in the vertical flare current-sheet that is embedded in the gravitationally stratified solar atmosphere and compared it with its gravity-free counterpart.

Methods. We adopted a two-dimensional (2D) magnetohydrodynamic (MHD) model, in which we solved a full set of ideal time-dependent MHD equations by means of the FLASH code, using the adaptive mesh refinement (AMR) method. To initiate the fast sausage magnetoacoustic waves, we used axisymmetric Gaussian velocity perturbation. As a diagnostic tool of these magnetoacoustic waves, we used the wavelet analysis method.

Results. We present a model of magnetoacoustic wave propagation with a gravity that is more realistic than that presented in previous studies. We compare our results with those of a gravity-free case. In equilibrium the current-sheet with gravity requires a non-zero horizontal component of the magnetic field, contrary to the gravity-free case. This causes differences in the parameters of the wave signal that propagates along the current sheet. In addition to these differences we find that wave signal variations and their wavelet tadpoles are more complex in the case with gravity than in the gravity-free case. Furthermore, for a shorter scale-height we found a prolongation of the wavelet tadpoles. These differences result from a variation of the dispersive properties and group velocities of the propagating magnetoacoustic waves with height in the solar atmosphere in the gravitational case. We show that these results can affect the diagnostics of physical processes in solar flares.