An international team working on prominence research, known as PROM, met at NSO/Kitt Peak from 8-10 April 1999. On 9 April, the team was joined in the NOAO main conference room by several members of the NSO and Solar Physics Research Corporation (SPRC) staff for an all day review and discussion of new topics of research. Key subjects were counterstreaming in prominences, the chirality of prominences and their environment, and X-ray features associated with prominences. When seen against the disk, prominences are now commonly called "filaments."
The morning session centered around the topic of counterstreaming which is a fine-scale pattern of oppositely directed flows everywhere within filaments. In a movie of counterstreaming in a filament observed by Jack Zirker (NSO), Oddbjorn Engvold (University of Oslo), and Sara Martin (Helio Research), it was demonstrated that counterstreaming is most clearly seen near the limb in observations made during very good seeing. The movie reveals a filament to have the same shape in the red or blue wing of the hydrogen alpha line. However, in the red wing the flows are typically along the axis but toward the limb and upward in the filament barbs (away from the observer). In the blue wing, the motions are typically along the axis toward disk center and downward in the barbs (toward the observer). Many diverse ideas were discussed about the cause of this bi-directional streaming. It implies that magnetic support of filament mass is insufficient to explain the existence of prominence mass in nearly vertical filament structures called barbs.
One of the highlights of the afternoon session was the presentation by Karen Harvey (SPRC) of linear Xray features above and nearly parallel to the axis of some filaments seen in Yohkoh images. Another highlight was Yuri Litvinenko's (University of New Hampshire) presentation of theory relating canceling magnetic fields to filament formation. Jack Harvey presented processed Kitt Peak line-of-sight magnetograms, which reveal areas of horizontal magnetic field in filament channels as well as around the borders of active regions.
During the workshop, the team reviewed and studied observational material from two observing runs in 1998 from a number of observatories. High quality observations obtained in June 1998 at the Swedish Solar Observatory in La Palma revealed counterstreaming and an unexpected pattern of apparent coherent motions in adjacent prominence threads of high latitude prominence. Additional discussions centered around theory relevant to counterstreaming and observations needed to better develop realistic prominence models.
Sara Martin