The Effect of Retardation on the Stability of Current Filaments
Abstract
We investigate the influence of the finite Alfvén velocity on the evolution of an active region filament. In general, variations of a current result in variations of the magnetic fields which spread around with the Alfvén velocity. As a consequence of the fact that a magnetic field can only change with the Alfvén velocity, a filament will experience the photospheric boundary conditions as these were at an Alfvén travel time back in time. The inclusion of this retardation effect in the momentum equation of a filament leads effectively to an extra force term. This force contribution acts in the direction in which the filament moves and has therefore a destabilizing effect on the filament. Because a moving filament acts as an antenna of Alfvén waves, the filament loses energy by the emission process. This leads to a radiative damping term in the equation of motion of the filament. In general, the radiative damping will be sufficiently strong to counteract the retardation instability. Numerical simulations show that during the energy buildup phase a filament follows the van TendKuperus equilibrium curve. After the van TendKuperus equilibrium has disappeared the filament goes through a transient phase moving with a subAlfvénic velocity upward. At greater heights the repulsive Lorentz force of the photospheric surface current magnetic field is balanced by the radiative damping, resulting in a decreasing filament velocity.
 Publication:

Solar Physics
 Pub Date:
 November 1992
 DOI:
 10.1007/BF00156636
 Bibcode:
 1992SoPh..142..113V
 Keywords:

 Magnetohydrodynamic Stability;
 Magnetohydrodynamic Waves;
 Propagation Velocity;
 Solar Prominences;
 Photosphere;
 Solar Magnetic Field;
 Solar Physics