Internal Shocks in the Reconnection Jet

S.Tanuma

The space solar missions such as Yohkoh and RHESSI observe the hard X-
and gamma-ray emission from energetic electrons in impulsive solar
flares. The energization mechanism of these particles, however, is not
known. In this paper, we suggest that the internal shocks are created
in the reconnection jet and that they are possible sites of particle
acceleration. We examine how the magnetic reconnection creates the
multiple shocks by performing two-dimensional resistive
magnetohydrodynamic simulations. In this paper, we use very small grid
to resolve the diffusion region. As the results, we find that the
current sheet evolves as follows: It becomes thin due to the tearing
instability, and it collapses to Sweet-Parker current sheet. The thin
sheet becomes unstable to tearing instability again. The fast
reconnection starts by the onset of anomalous resistivity immediately
after the secondary tearing instability. During the fast reconnection,
many plasmoids are created the secondary tearing instability and
ejected along the current sheet so that internal shocks are created in
the reconnection jet. This situation is a turbulent reconnection. We
suggest that the multiple fast shocks are created in the jet and that
the energetic electrons can be accelerated by them.