TURBULENT VELOCITY FIELDS IN QUIESCENT PROMINENCES

The velocity fields of prominences are derived from measurements of CaII K-line shifts in high resolution spectrograms. The turbulent character of the velocity field has been reported earlier (Jensen, 1982). That work was based on spectra of 4 large prominences observed at Oslo Solar Observatory. A much larger set of data is now beeing analysed. These spectrograms are recorded with the main spectrograph at the tower telescope at the Sacramento Peak Observatory. Details of observations are given in an earlier paper (Engvold, 1978). We shall here present and discuss the results obtained from nine quiescent prominences observed during 1973–74. The spectrograms have been analysed by means of the rapid scanning, computer controlled microphotometer of Institute of Theoretical Astrophysics, University of Oslo. The digitally recorded displacements within a given velocity-interval, giving the distribution of radial velocities, was denoted by N(u). In well-observed cases altogether 3–4000 profiles were obtained. Gaussian distributions were then fitted to the observed velocity-distributions by a least square procedure, giving a dependence of the form; N(u) ∝ exp (−(u−uo)2/α2). Here uo represent the combined rotational and bulk radial velocities, while α is a characteristic velocity parameter, describing the “turbulent exitation” in the prominence. In only one of the prominences investigated, did the velocity-distribution seem completely random and could not be represented by a Gaussian. In all the other cases the correlation-coefficient, r2, came out in excess of 0.9. This result indicates that the velocity-field, at least to a first approximation, may be assumed to be isotropic and stationary.