Shestov, S. ; Nakariakov, V. M. ; Reva, A. ; Ulyanov, A. ; Kuzin, S.

Talk presented at IBUKS 2016, KU Leuven, Leuven, Belgium on 2016-06-15

Abstract: Torsional Alfven waves are a type of magnetohydrodynamic waves in a non-uniform plasma, that travel at the Alfven speed along the magnetic field. In a straight field-aligned magnetic flux tube, these waves are azimuthal perturbations of the plasma velocity that are accompanied by an azimuthal component of the magnetic field. The torsional waves are important because they may play role in coronal heating, efficiently transferring energy from lower solar atmosphere layers to corona (Ofman, 2005; Murawski 2015) and the wind acceleration. In the linear regime torsional Alfven waves are considered to be non-compressible. Vasheghani Farahani et al. (2011, 2012) found that non-linear interactions of torsional Alfven waves result in various effects, such as development of longitudinal waves, wave profile steeping etc. We performed a numerical study of torsional Alfven waves dynamics in a straight magnetic flux tube, aiming to verify the analytical findings and extend them on the strongly nonlinear regime. We used MPI-AMRVAC code, set up an equilibrium magnetic flux tube with a finite-beta plasma and applied torsional perturbations of velocity and magnetic field at one of the tubes boundary. Non-linear interaction of torsional wave components resulted in development of two longitudinal waves propagating along the tubes axis, the first one with the tube speed, the second one with the Alfven speed. The behaviour of the simulated torsional wave in general conformed to theory.

Keyword(s): MHD ; Alfven waves ; nonlinear dynamics ; modeling