  Spectroscopic measurements of AR NOAA 10871, obtained with the Extreme
Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument on
2006 April 12, reveal velocity oscillations in the He II 303.8 Angstrom
emission line formed at T ~ 50000K. The oscillations appear to arise in a
bright active-region loop arcade about 25" wide which crosses the EUNIS slit.
The period of these transition region oscillations is 26 +/- 4 s, coupled with
a velocity amplitude of +/- 10 km/s, detected over 4 complete cycles. Similar
oscillations are observed in lines formed at temperatures up to T ~ 400000K,
but we find no evidence for the coupling of these velocity oscillations with
corresponding phenomena in the corona. We interpret the detected oscillations
as originating from an almost purely adiabatic plasma, and infer that they are
generated by the resonant transmission of MHD waves through the lower
active-region atmospheres. Through use of seismological techniques, we
establish that the observed velocity oscillations display wave properties most
characteristic of fast-body global sausage modes.
