Slow magnetacoustic waves in magnetic arcades

¹ Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
e-mail: M.Gruszecki@warwick.ac.uk
² Central Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, 196140 St Petersburg, Russia

Received: 23 June 2011
Accepted: 21 October 2011

Abstract

Aims. We investigate two-dimensional effects on the evolution of impulsively-generated slow magnetoacoustic waves in magnetic arcades of the solar corona.

Methods. We used a two-dimensional box model of a coronal arcade, neglecting the effects of gravity and magnetic curvature. Ideal finite-β magnetohydrodynamic equations were employed. The plasma was taken to be uniform, penetrated by a straight and uniform magnetic field. We applied line-tying boundary conditions at the magnetic footpoints.

Results. Running and standing slow magnetoacoustic waves develop across the magnetic field due to the reflection from the footpoints in the arcade. The perpendicular group speed is lower than both sound and Alfvén speeds. The speed grows with the increase in plasma-β, which is consistent with analytical theory. Slow magnetoacoustic pulse perturbs the magnetic field and current density; this effect is stronger for higher amplitudes. Standing waves spread across the field, forming a characteristic phase-mixing pattern of anti-parallel flows. The two-dimensional effects are more pronounced for higher β. Our results confirm the plausibility of the interpretation of the observed evolution of two-ribbon flares in terms of slow magnetoacoustic waves in magnetic arcades.