Spatially resolved observation of the fundamental and second harmonic standing kink modes using SDO/AIA^⋆

Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, CV4 7AL, UK
e-mail: D.J.Pascoe@warwick.ac.uk

Received: 25 April 2016
Accepted: 23 June 2016

Abstract

Aims. We consider a coronal loop kink oscillation observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) which demonstrates two strong spectral components. The period of the lower frequency component being approximately twice that of the shorter frequency component suggests the presence of harmonics.

Methods. We examine the presence of two longitudinal harmonics by investigating the spatial dependence of the loop oscillation. The time-dependent displacement of the loop is measured at 15 locations along the loop axis. For each position the displacement is fitted as the sum of two damped sinusoids, having periods P₁ and P₂, and a damping time τ. The shorter period component exhibits anti-phase oscillations in the loop legs.

Results. We interpret the observation in terms of the first (global or fundamental) and second longitudinal harmonics of the standing kink mode. The strong excitation of the second harmonic appears connected to the preceding coronal mass ejection (CME) which displaced one of the loop legs. The oscillation parameters found are P₁ = 5.00±0.62 min, P₂ = 2.20±0.23 min, P₁/ 2P₂ = 1.15±0.22, and τ/P = 3.35 ± 1.45.