Propagating slow magnetoacoustic waves in coronal loops observed by Hinode/EIS

TL;DR

This study reports the first Hinode/EIS observations of 5-minute slow magnetoacoustic waves propagating in coronal loops, showing their characteristics, damping behavior, and potential for coronal seismology.

Contribution

It provides new observational evidence of slow magnetoacoustic waves in coronal loops and analyzes their temperature-dependent damping, aiding coronal seismology.

Findings

Detected quasi-periodic oscillations in multiple lines at loop footpoints.

Oscillation amplitude decreases with increasing temperature.

Oscillations are consistent with slow magnetoacoustic waves propagating upward.

Abstract

We present the first Hinode/EIS observations of 5 min quasi-periodic oscillations detected in a transition-region line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV, and Fe XV) at the footpoint of a coronal loop. The oscillations exist throughout the whole observation, characterized by a series of wave packets with nearly constant period, typically persisting for 4-6 cycles with a lifetime of 20-30 min. There is an approximate in-phase relation between Doppler shift and intensity oscillations. This provides evidence for slow magnetoacoustic waves propagating upwards from the transition region into the corona. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. The amplitude of Doppler shift oscillations decrease by a factor of about 3, while that of relative intensity decreases by a factor of about 4 from Fe X to Fe XV. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by TRACE. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Thus, this property may have potential value for coronal seismology in diagnostic of temperature structure in a coronal loop.