Hot loop oscillations seen by sumer: Examples and statistics

We measure physical parameters of Doppler-shift oscillations in 17 flare-like events. These events have been recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on SOHO, along a slit fixed above limb active regions. The selected spectral windows contain emission lines with formation temperatures from ∼ 10⁴ to 10⁷ K. The events were only detected in hot flare lines, without any signature in lines formed around 2 × 10⁶ K. Similarly, the Doppler shift oscillations occur in regions coincident with hot soft X-ray loops, but not with EUV loops. The oscillations have periods of 11-31 min, with an exponential decay time of 5.5- 29 min, and show an initial large shift pulse with peak velocities up to 200 km s¹. Several indications suggest that the Doppler oscillations are incompressible coronal loop oscillations, that are usually excited impulsively by weak flare (or microflare) events that also produced a strong emission increase at 5 -8 × 10⁶ K.