Title:

Magnetic Flux Ropes in the Solar Atmosphere



A. A. van Ballegooijen
Smithsonian Astrophysical Observatory



Abstract:

Solar flares and coronal mass ejections are caused by the release of
magnetic free energy in the corona. This energy is stored in the form
of coronal flux ropes, highly sheared and/or twisted magnetic fields
located above polarity inversion lines in the photosphere. The flux
ropes are normally held down by overlying coronal arcades, but
occasionally they lose equilibrium, causing plasma and magnetic fields
to be ejected into the heliosphere. These eruptions can have dramatic
effects on the Earth's environment. Solar prominences (also known as
filaments) are cool plasmas located in such flux ropes and supported
by the magnetic field. I discuss the structure and formation of
coronal flux ropes. Models of flux rope formation suggest that the
helical field is formed not by twisting but rather by reconnection
of magnetic field lines associated with flux cancellation in the
photosphere. Magnetic diffusion may also play an important role by
dissipating some of the excess twist in the coronal flux ropes.
Empirical models of the coronal field can be constructed from filament
observations, and from vector field measurements such as those
provided by the Imaging Vector Magnetograph. Recent progress in
constructing such models is presented.