Tangled Magnetic Fields in Solar Prominences
Steven R Cranmer Submitted: 2010-01-18 12:06
Solar prominences are an important tool for studying the structure and
evolution of the coronal magnetic field. Here we consider so-called ''hedgerow''
prominences, which consist of thin vertical threads. We explore the
possibility that such prominences are supported by tangled magnetic fields.
A variety of different approaches are used. First, the dynamics of plasma
within a tangled field is considered. We find that the contorted shape of
the flux tubes significantly reduces the flow velocity compared to the
supersonic free fall that would occur in a straight vertical tube. Second,
linear force-free models of tangled fields are developed, and the elastic
response of such fields to gravitational forces is considered. We
demonstrate that the prominence plasma can be supported by the magnetic
pressure of a tangled field that pervades not only the observed dense
threads but also their local surroundings. Tangled fields with field
strengths of about 10 G are able to support prominence threads with observed
hydrogen density of the order of 1011 cm-3. Finally, we suggest that
the observed vertical threads are the result of Rayleigh-Taylor instability.
Simulations of the density distribution within a prominence thread indicate
that the peak density is much larger than the average density. We conclude
that tangled fields provide a viable mechanism for magnetic support of
Authors: A. A. van Ballegooijen and S. R. Cranmer
Publication Status: ApJ, in press.
Last Modified: 2010-01-18 13:06