Multiple-thread model of a prominence observed by SUMER and EIT on SOHO

A quiescent polar crown prominence was observed at Meudon in H alpha and Ca ii lines, and by EIT and SUMER on board SOHO in UV lines from 9 to 10 Marc h 1996. SUMER observed the prominence continuously in a scanning mode betwe en 21:40 UT on 9 March, and 18:13 UT on 10 March, in the nitrogen line N v (lambda 1238) with a 1 arc sec(2) resolution. Altogether 190 prominence ima ges (121 x 108 pixels) were obtained. These are presented in a movie. The p rominence is highly dynamic. Large-scale features, such as mixed loop syste ms and dark cavities are changing on time scales of a few hours. Filamentar y structure is evident and is changing within a few frames of the movie. A lifetime of 20-25 min for the fine structure has been found by the autocorr elation method. We have statistically analysed the three moments of the N v line in the prominence: line intensity, Doppler shift and linewidth, in th e context of a multiple-thread model. We find that the data are consistent with a model where the prominence is assumed to be an ensemble of small thr eads. In the brightest parts of the prominence it is possible that there ar e many unresolved threads (15-20) along the line of sight with diameters sm aller than a few hundred kilometers. The filling factor is probably very sm all and in that case the structures occupy only a fraction of the volume.