Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh41a1613p&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH41A-1613
Physics
7507 Chromosphere, 7509 Corona, 7524 Magnetic Fields, 7526 Magnetic Reconnection (2723, 7835), 7529 Photosphere
Scientific paper
Plasmas in prominences (filaments against the disk) exhibit a very wide spectrum of different kind of motions. Here we analyze the plasma motions inside prominences observed by Hinode/SOT during 2006-2007 with focus on two spectacular examples from 25 April 2007 in Halpha line and 30 November 2006 in CaH line and then carry out some simulations of the possible dynamics. Most filaments are composed of fine threads of similar dimensions rooted in the chromosphere/photosphere. Recent observations of counter-streaming motions together with oscillations along the threads provide strong evidence that the threads are field aligned. To more correctly interpret the nature of observed downward flows of dense and cool plasma as well as the upward dark flows of less dense plasma, we take into account the geometry of the prominence structures and the viewing angle. The dark upflows exhibit turbulent patterns such as vortex formation and shedding that are consistent with the motions predicted by instabilities of the interchange type. Sometimes an appearance of dark motions is generated by dark voids opened in the prominence sheet after initiation of nearby downflow streams, implying mass drainage in the downflows. Based on 304 A observations, there is more filament mass in prominences than is visible in either the Halpha 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 and also to the presence of Rayleigh-Taylor type or ballooning/interchange instabilities in the upper regions of the prominence. Transverse motions of filament threads caused by magnetic instabilities constantly provide the conditions for reconnection in the low part of the corona and the chromosphere. We suggest that the combination of flows along field lines, shear, and unstable stratification may provide the answers to the intriguingly elegant motions seen in prominences.
Landi Simone
Panasenco Olga
Velli M. M.
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