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 build-up phase a filament follows the van Tend-Kuperus equilibrium curve. After the van Tend-Kuperus equilibrium has disappeared the filament goes through a transient phase moving with a sub-Alfvénic 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.
Similar content being viewed by others
References
Anzer, U. and Ballester, J. L.: 1990, Astron. Astrophys. 238, 365.
Barnett, A. and Olbert, S.: 1986, J. Geophys. Res. 91, 10117.
Démoulin, P.: 1989, Thesis, University of Paris VII.
Démoulin, P. and Priest, E. R.: 1988, Astron. Astrophys. 206, 336.
Dobrowolny, M. and Veltri, P.: 1986, Astron. Astrophys. 167, 179.
Drell, S. D., Foley, H. M., and Ruderman, M. A.: 1965, J. Geophys. Res. 70, 3131.
Jackson, J. D.: 1975, Classical Electrodynamics, Wiley and Sons, New York, Ch. 17.2.
Kaastra, J. S.: 1985, Thesis, University of Utrecht.
Kippenhahn, R. and Schlüter, A.: 1957, Z. Astrophys. 43, 36.
Kuperus, M. and Raadu, M. A.: 1974, Astron. Astrophys. 31, 189.
Kuperus, M. and van Tend, M.: 1981, Solar Phys. 71, 125.
Leroy, J. L., Bommier, V., and Sahal-Bréchot, S.: 1983, Solar Phys. 83, 135.
Leroy, J. L., Bommier, V., and Sahal-Bréchot, S.: 1984, Astron. Astrophys. 131, 33.
Mazrtens, P. C. H. and Kuin, N. P. M.: 1989, Solar Phys. 122, 263.
Thompson, W. T. and Schmieder, B.: 1991, Astron. Astrophys. 243, 501.
van den Oord, G. H. J.: 1988, Astron. Astrophys. 205, 167.
van Tend, W.: 1979, Thesis, University of Utrecht.
van Tend, W. and Kuperus, M.: 1978, Solar Phys. 59, 115.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Van Den Oord, G.H.J., Kuperus, M. The effect of retardation on the stability of current filaments. Sol Phys 142, 113–129 (1992). https://doi.org/10.1007/BF00156636
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00156636