Signatures of Damping Nonlinear Oscillations by KHI-induced Turbulence in Synthetic Observations

TL;DR

This study uses 3D MHD simulations and synthetic EUV images to identify signatures of nonlinear damping by KHI-induced turbulence in coronal loop oscillations, enhancing understanding of solar coronal dynamics.

Contribution

It provides the first detailed observational signatures of KHI-driven turbulence damping in coronal loop oscillations through combined simulations and forward modeling.

Findings

Simulated oscillations show frequency shifts and damping consistent with turbulence theory.

Hotter channels exhibit faster decay and larger phase shifts in oscillations.

Early-stage synthetic oscillations closely match simulations, but later stages show turbulence effects.

Abstract

Large-amplitude decaying kink oscillations of coronal loops are strongly influenced by nonlinear processes, such as Kelvin-Helmholtz instability (KHI) and turbulence, though comprehensive theory and observational confirmation remain limited. Building on the recently developed theory on nonlinear damping by KHI-induced turbulence in impulsively driven transverse loop oscillations, we investigate its observational signatures using 3D magnetohydrodynamic simulations and forward-modelled EUV images. The simulated oscillations exhibit time-varying frequency shifts and damping rates, which are broadly consistent with nonlinear turbulence-damping theory. Additionally, they exhibit excitation of higher-order modes, slightly increased periods relative to the linear kink period, and reduced displacement amplitudes. These features are generally preserved in synthetic observations, though resolving higher-order modes requires higher spatial resolution than currently available. For loops embedded in a hotter background, hotter channels (e.g., 193 Angstroms) are more sensitive to boundary dynamics, thus their oscillations decay faster with smaller displacements and larger phase shifts than those in cooler channels (e.g., 171 Angstroms). Comparisons of simulated and synthetic oscillations show close agreement at the early stage. At later times, synthetic oscillations exhibit smaller displacements and larger phase shifts, due to turbulence-induced asymmetry in the loop cross-section. Bayesian fitting shows that the initial oscillation amplitude and kink period are robustly constrained, whereas parameters controlling the damping profile are degenerate, indicating that additional observables would aid reliable seismological inference. These results provide a quantitative basis for identifying nonlinear damping and detecting KHI-driven turbulence in transverse loop oscillations.