YOHKOH OBSERVATIONS OF AN OVER-THE-LIMB SOLAR-FLARE WITH LARGE SPECTRAL-LINE SHIFTS

We present observations of a solar hare of 1993 April 15 near 9 UT, us ing data from the Yohkoh Bragg crystal spectrometer (BCS) and soft X-r ay telescope (SXT). Observations from SXT indicate that the flare occu rred well beyond the solar limb, meaning that our observations are res tricted to the uppermost portions of the flaring structure. BCS spectr a show strong bulk blueshifts of the spectral line profiles for a shor t period near the start of the event, followed by an extended period o f strong bulk redshifts of the line profiles. Concurrent with these bu lk line shifts, the spectra show ''blue wing'' asymmetries. Both bulk line shifts and blue wings are infrequent characteristics of flares ob served near the solar limb. Our observations are consistent with stron g upward mass motions occurring on a high-altitude flaring loop orient ed edge-on with the Earth. We find nonthermal line broadenings in the spectra which are qualitatively and quantitatively similar to line bro adenings in spectra of disk flares. Near peak intensity of the flare, less than or similar to 10% of the residual nonthermal broadening can be explained by the spatial distribution of the soft X-ray flaring str ucture.