Propagating disturbances along a coronal loop from simultaneous EUV imaging and spectroscopic observations

Abstract

Propagating disturbances (PDs) were studied along an active region loop using simultaneous imaging and spectroscopy. An image sequence recorded in the Fe IX/Fe X 171Å channel, from TRACE and spectral data in the Si XII 520.6 Å line obtained from CDS/SOHO, are analyzed. A space-time map constructed from the TRACE image sequence shows the presence of PDs close to the loop foot point propagating with an apparent speed of 39 km s−1. The periodicity was found to be 5.4 min. The corresponding spectroscopic data from CDS, at a location away from the foot point, show oscillations in all three line parameters roughly at the same period. At locations farther from the foot point, the line width oscillation seems to disappear while the Doppler velocity oscillation becomes prominent. We attribute this to the signature of propagating slow waves that get affected by flows/other events close to the foot point. Spectral line profiles do not show much asymmetry, however, it is difficult to infer anything due to the broadened Gaussian shape of the CDS line profiles.