Are magnetic null points important in solar flares ?

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

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 1994 vol. 285 p. 1023 - 1037

0004-6361

When they are present, null points (points where the 3 components of the magnetic field vanish) determine the topology of the magnetic field configuration. It has been suggested that the presence of nulls is related to flares, and that they settle the region where the energy is released by magnetic reconnection. Since solar flares are initially coronal events, nulls should be located above the photosphere. Therefore, we investigate the location of nulls in configurations formed by a parasitic and a main bipole (4 magnetic sources). For both potential and linear-force free field approaches, we have found that a null was present in the corona only when the two bipoles were nearly antiparallel. The flaring regions analysed here are those where the magnetic topology has been related to flare kernels in previous papers. These observations show that flares occur for any horizontal orientation of the parasitic bipole to the main one, having only in particular cases a null in the extrapolated field. When a null is present, it can be at any place along the separator and it is not necessarily related to the region where the energy is released. These results are found both in the subflares and the intense X-ray flares studied. Examples of observed configurations that can be analysed with 2D or 3D models are presented. We conclude that nulls above the photosphere are not needed for flaring but that the spatial properties of the coronal field still determines the location where reconnection takes place. Results are discuss in the context of present understanding of 3D reconnection.