Abstract
Nonuniform plasma across an imposed magnetic field, such as those present in the solar atmosphere, can support collective Alfvénic oscillations with a characteristic damping time. The damped transverse oscillations of coronal loops are an example of this process. In ideal magnetohydrodynamics (MHD), these transient collective motions are associated with quasi-modes resonant in the Alfvén continuum. Quasi-modes live in a non-principal Riemann sheet of the dispersion relation, and so they are not true ideal MHD eigenmodes. The present study considers the illustrative case of incompressible surface MHD waves propagating on a nonuniform interface between two uniform plasmas with a straight magnetic field parallel to the interface. It is explored how the ideal quasi-modes of this configuration change when the width of the nonuniform transition increases. It is found that interfaces with wide enough transitions are not able to support truly collective oscillations. A quasi-mode that can be related with a resonantly damped surface MHD wave can only be found in interfaces with sufficiently thin transitions.
Funder
Agencia Estatal de Investigacion
Subject
General Physics and Astronomy
Reference29 articles.
1. Field topologies in ideal and near-ideal magnetohydrodynamics and vortex dynamics;Sci. China Phys. Mech. Astron.,2015
2. Magnetohydrodynamic waves in the solar corona;Annu. Rev. Astron. Astrophys.,2020
3. Hydromagnetic surface waves;Astrophys. J.,1979
4. Wave propagation in a magnetically structured atmosphere. I: Surface waves at a magnetic interface;Sol. Phys.,1981
5. Surface Alfvén waves in solar flux tubes;Astrophys. J.,2012