Transition from decaying to decayless kink oscillations of solar coronal loops

TL;DR

This paper models the transition from decaying to decayless kink oscillations in solar coronal loops, revealing a non-exponential damping pattern influenced by external flows and initial amplitude, with implications for solar coronal seismology.

Contribution

It introduces a self-oscillation model explaining decayless kink oscillations and their damping patterns, incorporating external flow interactions and providing analytical and observational validation.

Findings

Damping pattern is non-exponential and depends on initial amplitude and coupling parameter.

Rapid decay to stationary amplitude can occur within less than an oscillation period.

Model aligns well with observational data and offers new insights into coronal loop oscillations.

Abstract

The transition of an impulsively excited kink oscillation of a solar coronal loop to an oscillation with a stationary amplitude, i.e., the damping pattern, is determined using the low-dimensional self-oscillation model. In the model, the decayless kink oscillations are sustained by the interaction of the oscillating loop with an external quasi-steady flow. The analytical solution is based on the assumption that the combined effect of the effective dissipation, for example, by resonant absorption, and interaction with an external flow, is weak. The effect is characterised by a dimensionless coupling parameter. The damping pattern is found to depend upon the initial amplitude and the coupling parameter. The approximate expression shows a good agreement with a numerical solution of the self-oscillation equation. The plausibility of the established damping pattern is demonstrated by an observational example. Notably, the damping pattern is not exponential, and the characteristic decay time is different from the time determined by the traditionally used exponential damping fit. Implications of this finding for seismology of the solar coronal plasmas are discussed. In particular, it is suggested that a very rapid, in less than the oscillation period, decay of the oscillation to the stationary level, achieved for larger values of the coupling parameter, can explain the relative rareness of the kink oscillation events.