Interaction of Large-scale Magnetic Structures in Solar Flares

MANDRINI, C.H.; DÉMOULIN, P.; HÉNOUX, J.C.

Iguazú

Congreso; International Astronomical Union Colloquium 133; 1991

Modelling the observed vertical magnetic field of active region (AR) NOAA 2372 by the potential field of an ensemble of magnetic dipoles, we have derived the likely location of the separatrices, surfaces that separate cells of different field line connectivities, and of the separator which is the intersection of the separatrices. The connectivity of every magnetic field line, which is defined by the dipoles located at its ends, is computed by a code that, starting from any pixel in the photospheric plane, integrates numerically the differential equation defining a line of force towards both ends of this line until one dipole is reached. This code allows us to obtain the topology of the field in three dimensions. We have compared our results with observations of a 1B/M1 flare that developed in AR 2372 on April 6, 1980 at 20:53 UT (Lin and Gaizauskas, 1987), twenty minutes before obtaining the magnetogram. We found that four of the five off-band Ha kernels were located near or at the separatrices. These Ha kernels are connected by field lines that pass close to the separator. This indicates that the flare may have resulted from the interaction of large scale magnetic structures in the separator region. Moreover, Lin and Gaizauskas (1987) showed that the Ha flare kernels coincided with the peak values of the longitudinal electric current density. This finding and the fact that no strong current and no Ha kernel are observed at the intersection of the separator with the photosphere, lead to the conclusion that the magnetic energy released during the flare is mostly stored in an ensemble of currents flowing along lines of force. Some instability, presumably due to reconnection taking place in the separator, is likely to be the origin of the energy release and of the observed flare.