Spatial damping of propagating kink waves due to mode coupling

D. J. Pascoe, A. W. Hood, I. De Moortel and A. N. Wright

School of Mathematics and Statistics, University of St Andrews, St Andrews KY16 9SS, UK
e-mail: dpascoe@mcs.st-and.ac.uk

Received: 30 August 2011
Accepted: 12 December 2011

Abstract

Aims. We investigate the damping process for propagating transverse velocity oscillations, observed to be ubiquitous in the solar corona, due to mode coupling.

Methods. We perform 3D numerical simulations of footpoint-driven transverse waves propagating in a low β coronal plasma with a cylindrical density structure. Mode coupling in an inhomogeneous layer leads to the coupling of the kink mode to the Alfvén mode, observed as the decay of the transverse kink oscillations.

Results. We consider the spatial damping profile and find a Gaussian damping profile of the form exp(-z²/L_g²) to be the most congruent with our numerical data, rather than the exponential damping profile of the form exp(− z/L_d) used in normal mode analysis. Our results highlight that the nature of the driver itself will have a substantial influence on observed propagating kink waves.

Conclusions. Our study suggests that this modified damping profile should be taken into account when using coronal seismology to infer local plasma properties from observed damped oscillations.