Doppler Shift, Intensity, and Density Oscillations Observed with the EUV Imaging Spectrometer on Hinode

TL;DR

This study reports on Doppler-shift, intensity, and density oscillations observed in the solar corona using Hinode's EIS, identifying upward propagating slow magnetoacoustic waves with typical 10-minute periods.

Contribution

It provides new observations of coronal oscillations in active regions, including Doppler, intensity, and density variations, and links these to slow magnetoacoustic wave modes.

Findings

Doppler-shift oscillations with 1-2 km/s amplitude

Oscillations with ~10-minute periods

Evidence for upward propagating slow magnetoacoustic waves

Abstract

Low-amplitude Doppler-shift oscillations have been observed in coronal emission lines in a number of active regions with the EUV Imaging Spectrometer (EIS) on the Hinode satellite. Both standing and propagating waves have been detected and many periods have been observed, but a clear picture of all the wave modes that might be associated with active regions has not yet emerged. In this study, we examine additional observations obtained with EIS in plage near an active region on 2007 August 22--23. We find Doppler-shift oscillations with amplitudes between 1 and 2 km/s in emission lines ranging from Fe XI 188.23 Angstroms, which is formed at log T = 6.07 to Fe XV 284.16 Angstroms, which is formed at log T = 6.32. Typical periods are near 10 minutes. We also observe intensity and density oscillations for some of the detected Doppler-shift oscillations. In the better-observed cases, the oscillations are consistent with upwardly propagating slow magnetoacoustic waves. Simultaneous observations of the Ca II H line with the Hinode Solar Optical Telescope Broadband Filter Imager show some evidence for 10-minute oscillations as well.