Apparent cross-field superslow propagation of magnetohydrodynamic waves in solar plasmas

In this paper we show that the phase mixing of continuum Alfvén wavesand/or continuum slow waves in magnetic structures of the solar atmosphereas, e.g., coronal arcades, can create the illusion of wave propagation across themagnetic eld. This phenomenon could be erroneously interpreted as fast mag-netosonic waves. The cross-field propagation due to phase mixing of continuumwaves is apparent because there is no real propagation of energy across the magnetic surfaces. We investigate the continuous Alfvén and slow spectra in 2DCartesian equilibrium models with a purely poloidal magnetic field. We showthat apparent superslow propagation across the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén waves and continuum slow waves that naturally live on those structures and phase mix as time evolves. The apparent cross-field phase velocity is related to the spatial variation of the local Alfvén/slow frequency across the magnetic surfaces and is slower than the Alfvén/sound velocities for typical coronal conditions. Understanding the nature of the apparent cross-field propagation is important for the correct analysis of numerical simulations and the correct interpretation of observations