Vertical plasma motions in prominence sheets observed by Hinode
Abstract
We analyze the approximately vertical motions inside prominence plasma observed by Hinode on 25 April 2007 in Hα line and 30 November 2006 in CaH line. Well-established observational facts are that all filaments (prominences on the limb) are composed of fine threads of similar dimensions, rooted in the photosphere and presumably tracing magnetic field lines, and that continuous counter-streaming motions occur along threads. We take into account the geometry of the prominence sheet and the viewing angle to reduce possible projection effect and more correctly interpret the nature of observational downward flows of denser and cooler plasma as well as the upward flow of hotter plasma which appears dark in the Hα and CaH spectral lines. The dark upflows exhibit turbulent flow properties such as vortex formation and shedding that are consistent with the properties of thermal starting plumes. Sometimes an illusion of dark upward motion is generated by rarefactions in the plasma sheet caused by the cooler denser downward flows. On both dates, we suspect there is probably more filament mass in the prominence that is visible in either the Hα or CaH lines. The source of the downward moving plasma may be located either higher above the visible upper edge of the prominence or on the far end of the prominence spine. The bright downward motions of the more cool and dense plasma may be partly due to the counter-streaming motion along the magnetic fields lines, or it may be due to the presence of rayleigh-taylor type or ballooning/interchange instabilities in the upper regions of the prominence, which are then stabilized lower down where the magnetic field is stronger and the plasma beta lower.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.2337P