Kink instability as a driving mechanism for pinching of hyperbolic flux
tubes

Author List:
Titov, V., Kliem, B., Toeroek, T.

Abstract:
Using the analytical solution by Titov & Demoulin (1999) for a
force-free magnetic flux rope as the initial condition in 3D MHD
numerical simulations, we have investigated the development of the
helical kink instability in such a configuration. In spite of the
incorporated line-tying effect, this instability starts to develope when
the twist of magnetic field lines in the initial flux rope reaches
$3.5\pi$ for the particular set of parameters considered. During the
instability, a helical current layer wrapped around the kinking and
rising rope and vertical current layer below the rope are formed. The
latter is a result of pinching of hyperbolic flux tube (HFT) present in
the initial field by a stagnation-type flow induced by the moving rope.
The HFT consists of two intersecting quasi-separatrix layers with the
elastic properties favorable for pinching process. Our results
substantiate and complement the standard model of solar flares in which
the vertical current sheet is the central element. Essential features of
the initial phase of solar flares such as the formation of transient
soft X-ray sigmoids could be reproduced in simulations. However, at a
later phase, the kink perturbation starts to saturate and so a full
eruption of the configuration cannot be obtained without a significant
modification of the initial field, where the overlying field decreases
with hight faster than in the used model.

Poster:
No