ULTRAVIOLET CORONAGRAPH SPECTROMETER OBSERVATION OF THE 1996 DECEMBER23 CORONAL MASS EJECTION

The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and H eliospheric Observatory (SOHO) observed a spectacular coronal mass eje ction (CME) caused by a prominence eruption on 1996 December 23. The e volution of the ejected prominence material was followed for 1 hr and 50 minutes. The observation consists of a series of 5 minute exposures , at a fixed heliocentric distance of 1.5 R circle dot in several spec tral ranges. The Lyman lines of hydrogen brighten more than 2 orders o f magnitude during the CME. The C III 977.02 Angstrom line is very bri ght, and many other low-temperature lines have been detected. Line int ensities and profiles provide important diagnostics for the physical a nd dynamical parameters of the ejected plasma. Lines widths show nonth ermal line broadening due to a plasma expansion with velocity larger t han 50 km s(-1). The Ly alpha inside the CME region shows red and blue shifts, up to 0.2 Angstrom (50 km s(-1)) and 0.8 Angstrom (200 km s(- 1)), respectively. A preliminary estimate shows a flat emission measur e distribution 3 or 4 orders of magnitude smaller than typical promine nce emission measures. Essentially the same structure in space and vel ocity is seen in the Lyman lines, in C III (10(5) K) and in 0 VI (3 x 10(5) K).