Thermal non-equilibriuem revealed by periodic pulses of random amplitudes in solar coronal loops

TL;DR

This paper investigates periodic intensity variations in solar coronal loops, revealing they are caused by thermal non-equilibrium cycles characterized by random pulse trains, rather than vibrational modes.

Contribution

It demonstrates that observed coronal loop pulsations are due to aborted TNE cycles with random pulse amplitudes, confirmed through Fourier and wavelet analysis.

Findings

Periodic signals are not vibrational modes.

Power spectra show discrete harmonics and continua.

Pulsations are linked to aborted TNE cycles.

Abstract

We recently detected variations in extreme ultraviolet intensity in coronal loops repeating with periods of several hours. Models of loops including stratified and quasi-steady heating predict the development of a state of thermal non-equilibrium (TNE): cycles of evaporative upflows at the footpoints followed by falling condensations at the apex. Based on Fourier and wavelet analysis, we demonstrate that the observed periodic signals are indeed not signatures of vibrational modes. Instead, superimposed on the power law expected from the stochastic background emission, the power spectra of the time series exhibit the discrete harmonics and continua expected from periodic trains of pulses of random amplitudes. These characteristics reinforce our earlier interpretation of these pulsations as being aborted TNE cycles.