Solar Flares Caused by the Skin Effect in Twisted Magnetic Fields.
Abstract
An optical flare may be caused by the collapse of an unstable chromospheric region, under the action of magnetic forces, toward a surface of minimum but finite magnetic field strength. The compression of the magnetic field during the collapse results in forces which stop the collapse, in a time comparable to the rise time of flare light-curves Turbulence is likely to occur if the velocities of collapse can become comparable to Alfven speeds. The turbulence provides sufficient ohmic dissipation of the magnetic fields to explain the rate of optical emission. The emission is l6calixed in thin surfaces at the eddy boundaries. The total depth of the emitting surfaces crossed by a line of sight is in agreement with inferences from observations. If the same kind of collapse which causes an optical flare in the chromosphere occurs at greater heights, the density is insufficient to radiate away the thermal energy derived from ohmic dissipation. The result is heating, with attendant radio, X-ray, and particle events, instead of an optical flare. The conditions under which turbulence may occur are investigated Some of the consequences of the theory relate to flare light-curves, homologous flares, and rates of expansion of flare areas
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1964
- DOI:
- 10.1086/148059
- Bibcode:
- 1964ApJ...140.1563W