Magnetic topologies: where will reconnection occur ?
Pascal Demoulin Submitted: 2005-10-12 06:05
The energy needed to power flares is thought to come from the coronal
magnetic field. However, such energy release is efficient only at
very small scales. Magnetic configurations with a complex topology,
i.e. with separatrices, are the most obvious configurations where
current layers can spontaneously form. 3-D magnetic configurations
have a variety of magnetic topologies not suspected before. If the
photospheric field is described by an ensemble of magnetic charges,
separated by flux-free regions, a complete topological description of
the associated potential field is provided by the skeleton formed by
the null points, spines, fans and separators. In order to better
match the observed photospheric magnetograms, the magnetic charges can
be set below the photosphere; then an extra topological element can
appear, so-called bald patches with associated separatrices. In
several flaring configurations the computed separatrices allows to
understand the localization of the flare ribbons in the framework of
magnetic reconnection. However, this view is too restrictive taking
into account the variety of observed solar flaring configurations.
Indeed ``quasi-separatrix layers'' (QSLs), which are regions where
there is a drastic change in field-line linkage, generalize the
definition of separatrices for magnetic fields extending in the full
volume (photosphere and corona). The concept of ``hyperbolic flux
tube'' (HFT) also generalizes the concept of separator. These studies
indeed teach us that coronal magnetic reconnection occurs in a broader
variety of magnetic configurations than traditionally thought, and
this variety is reviewed.
Authors: Demoulin, P.
Publication Status: ESA publication, in press
Last Modified: 2005-10-12 06:05