J. W. Threlfall, C. E. Parnell, I. De Moortel, K. G. McClements, T. D. Arber
Context. This paper investigates the role of the Hall term in the propagation
and dissipation of waves which interact with 2D magnetic X-points and considers
the effect of the Hall term on the nature of the resulting reconnection. Aims.
The goal is to determine how the evolution of a nonlinear fast magnetoacoustic
wave pulse, and the behaviour of the oscillatory reconnection which results
from the interaction of the pulse with a line-tied 2D magnetic X-point, is
affected by the Hall term in the generalised Ohm's law. Methods. A Lagrangian
remap shock-capturing code (Lare2d) is used to study the evolution of an
initial fast magnetoacoustic wave annulus for a range of values of the ion skin
depth (di) in resistive Hall MHD. A magnetic null-point finding algorithm is
also used to locate and track the evolution of the multiple null-points that
are formed in the system. Results. In general, the fast wave is coupled to a
shear wave and, for finite di, to whistler and ion cyclotron waves. Dispersive
whistler effects cause rapid oscillations of the X-point, which (in combination
with the arrival of the main body of the pulse) leads to the creation of
magnetic islands and multiple null points under the influence of the Hall term.
At later times, competition of local Lorentz and gas pressure forces return the
system to a near-equilibrium state. The rate of oscillatory reconnection
recovered during this latter phase appears to be unaffected by the value of di.
View original:
http://arxiv.org/abs/1202.3648
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