Fast and Alfven waves driven by azimuthal footpoint motions

The excitation of Alfvén and fast magnetosonic waves in footpoint driven coronal loops is studied in the framework of resonant absorption. Previous studies revealed that in case of radial footpoint motions, quasi-modes are essential for effective wave dissipation in the loops [2, 4]. We now investigate the role they play in azimuthally driven loops. For a periodic driver, the efficiency of resonant absorption strongly depends on the driving frequency omega_(d): only for quasi-mode frequencies coupling has a positive effect on the growth of the (single) Alfven resonance. The problem of single-shell heating can be solved by considering a more realistic, random driver: a variety of resonant Alfven waves are excited and multiple resonant peaks appear, with length scales which are short enough for effective dissipation. When more realistic loop lengths are considered, the resonant surfaces are even more numerous resulting in globally heated loops.status: publishe