The Spectroscopic Signature of Quasi-periodic Upflows in Active Region Timeseries

TL;DR

This study uses spectroscopic and imaging data to demonstrate that quasi-periodic upflows, rather than waves, are responsible for observed oscillations in active region coronal emissions.

Contribution

It provides direct spectroscopic evidence linking quasi-periodic upflows to observed oscillations, challenging the traditional wave interpretation in active region dynamics.

Findings

Quasi-periodic upflows are correlated with intensity, Doppler shift, and line width oscillations.

No frequency doubling observed in line width oscillations.

Upflows are identified in both spectroscopic and imaging data, supporting their role in observed phenomena.

Abstract

Quasi-periodic propagating disturbances are frequently observed in coronal intensity image sequences. These disturbances have historically been interpreted as being the signature of slow-mode magnetoacoustic waves propagating into the corona. The detailed analysis of Hinode EUV Imaging Spectrometer (EIS) timeseries observations of an active region (known to contain propagating disturbances) shows strongly correlated, quasi-periodic, oscillations in intensity, Doppler shift, and line width. No frequency doubling is visible in the latter. The enhancements in the moments of the line profile are generally accompanied by a faint, quasi-periodically occurring, excess emission at ~100 km/s in the blue wing of coronal emission lines. The correspondence of quasi-periodic excess wing emission and the moments of the line profile indicates that repetitive high-velocity upflows are responsible for the oscillatory behavior observed. Furthermore, we show that the same quasi-periodic upflows can be directly identified in a simultaneous image sequence obtained by the Hinode X-Ray Telescope (XRT). These results are consistent with the recent assertion of De Pontieu & McIntosh (2010) that the wave interpretation of the data is not unique. Indeed, given that several instances are seen to propagate along the direction of the EIS slit that clearly show in-phase, quasi-periodic variations of intensity, velocity, width (without frequency doubling), and blue wing enhanced emission this dataset would appear to provide a compelling example that upflows are more likely to be the main cause of the quasi-periodicities observed here, as such correspondences are hard to reconcile in the wave paradigm.