Transverse Velocity Perturbations in Solar Coronal Loops

Astronomy Unit Seminars
Ineke de Moortel
David Tsiklauri
October 28th, 2016 at 14:30
GO Jones Room 610

In this talk, I will give an overview of transverse, propagating velocity perturbations observed in solar coronal loops. These ubiquitous perturbations are observed to contain substantial amounts of energy and undergo strong damping as they propagate. Using both numerical and analytical modelling, we demonstrate that these can be understood in terms of coupling of different wave modes in the inhomogeneous boundaries of the loops: we perform 3D numerical simulations of footpoint-driven transverse waves propagating in a coronal plasma with a cylindrical density structure. Mode coupling in the inhomogeneous boundary layers of the loops leads to the coupling of the transversal (kink) mode to the azimuthal (Alfvén) mode, observed as the decay of the transverse kink oscillations. In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter) Doppler shift observations of a large, off-limb, trans-equatorial loops system show that Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. We suggest that this excess high-frequency FFT power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvenic) turbulence, potentially contributing to heating of the loops.