Mode identification of MHD waves in an active region observed with Hinode/EIS

TL;DR

This study analyzes EUV spectroscopic data from Hinode to identify MHD wave modes in an active region, revealing the presence of kink, Alfvén, and slow-mode waves with implications for coronal heating.

Contribution

It provides a detailed mode identification of MHD waves in active regions using Fourier analysis of intensity and Doppler velocity data, highlighting the types and energy fluxes of observed waves.

Findings

Detection of kink and torsional Alfvén waves in moss regions and loop apexes.

Identification of upward propagating and standing slow-mode waves.

Wave energy fluxes are insufficient for active region heating.

Abstract

In order to better understand the possibility of coronal heating by MHD waves, we analyze Fe xii 195.12{\AA} data observed with EUV Imaging Spectrometer (EIS) onboard Hinode. We performed a Fourier analysis of EUV intensity and Doppler velocity time series data in the active region corona. Notable intensity and Doppler velocity oscillations were found for two moss regions out of the five studied, while only small oscillations were found for five apexes of loops. The amplitudes of the oscillations were 0.4 - 5.7% for intensity and 0.2 - 1.2 kms-1 for Doppler velocity. In addition, oscillations of only Doppler velocity were seen relatively less often in the data. We compared the amplitudes of intensity and those of Doppler velocity in order to identify MHD wave modes, and calculated the phase delays between Fourier components of intensity and those of Doppler velocity. The results are interpreted in terms of MHD waves as follows: (1) few kink modes or torsional Alfv'en mode waves were seen in both moss regions and the apexes of loops; (2) upwardly propagating and standing slowmode waves were found inmoss regions; and (3) consistent with previous studies, estimated values of energy flux of the waves were several orders of magnitude lower than that required for heating active regions.