The dynamics of driven magnetic reconnection in coronal arcades |
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Authors: | G J Rickard E R Priest |
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Institution: | (1) University of St. Andrews, St. Andrews, UK |
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Abstract: | The dynamics of interacting coronal loops and arcades have recently been highlighted by observations from theYohkoh satellite and may represent a viable mechanism for heating the solar corona. Here such an interaction is studied using two-dimensional
resistive magnetohydrodynamic (MHD) simulations. Initial potential field structures evolve in response to imposed photospheric
flows. In addition to the anticipated current sheet about theX-point separating the colliding flux systems, significant current layers are found to lie all the way along the separatrices
that intersect at theX-point and divide the coronal magnetic field into topologically distinct regions. Shear flows across the separatrices are
also observed. Both of these features are shown to be compatible with recent analytical studies of two-dimensional linear
steady-state magnetic reconnection, even though the driven system that has been simulated is not strictly ‘open’ in the sense
implied by steady-state calculations. The implications for future steady-state models are also discussed. The presence of
the neutral point also brings into question any constant-density approximations that have previously been used for such quasi-steady
coronal evolution models. This results from the intimate coupling between the neutral point and its separatrices communicated
via the gas pressure.
In terms of the detailed energetics during the arcade evolution, preliminary results reveal that on the order of 3% of the
energy injected by the footpoint motions is lost purely through ohmic dissipation. We would therefore anticipate a local hot
spot between the interacting flux systems, and a brightening distributed along the length of any separatrix field lines. Furthermore,
as the resistivityη is reduced, the flux annihilation rate and the ohmic dissipation rate are found to scale independently ofη. |
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