Previous abstract Next abstract

Session 2 - Everything Else.
Display session, Friday, June 27
Ballroom C, Chair: Richard Canfield

[2.34] Mean-Field Electrodynamics of the Solar Corona

A. A. Van Ballegooijen (Center for Astrophysics)

The magnetic field lines in the solar corona are subject to random motions of the photospheric footpoints due to their interaction with granulation and supergranulation flows. These random motions cause small-scale twisting and braiding of the coronal field, which leads to magnetic reconnection and heating of the coronal plasma. In this poster I present a mean-field theory which describes the effects of random footpoint motions on the evolution of the mean (spatially averaged) coronal magnetic field. The approach is similar to that used in kinematic dynamo theory, but unlike in dynamo theory the magnetic pressure is assumed to be large compared to the gas pressure, so that the magnetic field is nearly force-free. Another key assumption is that the photospheric motions are purely horizontal, so that the radial field at the photosphere obeys Leighton's (1964) diffusion equation. It is shown that magnetic diffusion in the corona can be described in terms of an anisotropic diffusion tensor which varies in space and time. The theory provides a formalism for computing the mean velocity in the corona, which is needed to determine the evolution of the mean magnetic field. Using a simple model of a decaying active region, it is shown that the mean velocity at the tops of coronal loops is directed downward, causing the magnetic shear in the region to be concentrated at the polarity inversion line. This may explain observations of localized shear in solar active regions, and could also play a role in the formation of filament channels on the quiet sun.

The author(s) of this abstract have provided an email address for comments about the abstract:

Program listing for Friday