Coronal loop slow mode oscillations driven by the kink instability

Centre for Fusion, Space and Astrophysics, Physics Department, Warwick University, Coventry, CV4 7AL, UK e-mail: martin.haynes@warwick.ac.uk

Received: 23 August 2007
Accepted: 7 December 2007

Abstract

Aims.To establish the dominant wave modes generated by an internal, kink instability in a short coronal flux tube.

Methods.The 3D MHD numerical simulations are performed using Lare3d to model the kink instability and the subsequent wave generation. The initial conditions are a straight, zero net current flux tube containing a twist higher than the kink instability threshold.

Results.It is shown that the kink instability initially sets up a harmonic ( overtone) that is converted through the rearrangement of the magnetic field into two out-of-phase fundamental slow modes. These slow modes are in the two entwined flux tubes created during the kink instability.

Conclusions.The long-lived oscillations established after a kink instability provide a possible way to identify whether sudden, short coronal loop brightenings may have resulted from a confined kink instability. The mode oscillation structure changes from the harmonic to fundamental due to field line relaxation. The subsequent decay in the fundamental mode is comparable to observations and is caused by shock dissipation. This result has important consequences for the damping of the slow mode oscillations observed by SUMER.