Doppler Shift Oscillations of Hot Solar Coronal Plasma Seen by SUMER: A Signature of Loop Oscillations?

Abstract

We report observations of strongly damped Doppler shift oscillations detected in a flare line, Fe xix, with the Solar Ultraviolet Measurement of Emitted Radiation spectrometer. Spectra were recorded above an active region at the western limb of the Sun, from lines with formation temperatures ranging from 0.01 to 10 MK. However, the oscillations were seen only in the hot plasma (16 MK) lines. The Doppler oscillations have periods of 14-18 minutes , with an exponential decay time of 12-19 minutes, and show an initial large blueshift pulse with peak velocities up to 77 km s 1. Several indications suggest that the Doppler oscillations are incompressible coronal loop oscillations that are excited impulsively by a flarelike event that also produced a strong increase in Fe xix emission.