Frequency-dependent Evolution of Propagating Intensity Disturbances in Polar Plumes

Quasiperiodic disturbances in EUV emission intensity, propagating along polar plumes in the solar corona, are frequently observed. Analysis of these propagating disturbances in the 171 Å bandpass of the Solar Dynamics Observatory/Atmospheric Imaging Assembly reveals that the wave spectrum evolves with height. Near the footpoints, the dominant spectral peak corresponds to oscillation periods of 12–15 minutes. As the disturbances propagate upward, the shorter-period spectral component diminishes, while a longer-period component of 20–30 minutes becomes dominant. Theoretical modeling of coronal slow magnetoacoustic waves effectively reproduces this spectral evolution. The model incorporates field-aligned thermal conduction and the back reaction of wave-induced perturbations on local thermal equilibrium. Coronal slow waves, driven by a broadband source with a peak at a shorter period, show a decrease in shorter-period spectral power with height, while the 20–30 minute spectral power increases due to thermal overstability. Analysis of the dispersion relations reveals that, given the chosen model parameters, the most rapidly growing spectral component corresponds to a 22.5 minute period, which aligns well with the observational findings.