Fan–Spine Topology Formation Through Two-Step Reconnection Driven by Twisted Flux Emergence

We address the formation of three-dimensional nullpoint topologies in the solar corona by combining Hinode/X-ray Telescope (XRT) observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a three-dimensional (3D) zero- Delta *b magnetohydrodynamics (MHD)...

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Bibliographic Details
Published in:The Astrophysical journal 2009-10, Vol.704 (1), p.485-495
Main Authors: Török, T, Aulanier, G, Schmieder, B, Reeves, K. K, Golub, L
Format: Article
Language:English
Subjects:
Astronomy
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
ATMOSPHERES
Earth, ocean, space
Exact sciences and technology
EXPANSION
FLUID MECHANICS
HYDRODYNAMICS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MAIN SEQUENCE STARS
MATHEMATICS
MECHANICS
Physics
SIMULATION
SOLAR ATMOSPHERE
SOLAR CORONA
STARS
STELLAR ATMOSPHERES
STELLAR CORONAE
SUN
TELESCOPES
THREE-DIMENSIONAL CALCULATIONS
TOPOLOGY
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Summary:We address the formation of three-dimensional nullpoint topologies in the solar corona by combining Hinode/X-ray Telescope (XRT) observations of a small dynamic limb event, which occurred beside a non-erupting prominence cavity, with a three-dimensional (3D) zero- Delta *b magnetohydrodynamics (MHD) simulation. To this end, we model the boundary-driven 'kinematic' emergence of a compact, intense, and uniformly twisted flux tube into a potential field arcade that overlies a weakly twisted coronal flux rope. The expansion of the emerging flux in the corona gives rise to the formation of a nullpoint at the interface of the emerging and the pre-existing fields. We unveil a two-step reconnection process at the nullpoint that eventually yields the formation of a broad 3D fan-spine configuration above the emerging bipole. The first reconnection involves emerging fields and a set of large-scale arcade field lines. It results in the launch of a torsional MHD wave that propagates along the arcades, and in the formation of a sheared loop system on one side of the emerging flux. The second reconnection occurs between these newly formed loops and remote arcade fields, and yields the formation of a second loop system on the opposite side of the emerging flux. The two loop systems collectively display an anenome pattern that is located below the fan surface. The flux that surrounds the inner spine field line of the nullpoint retains a fraction of the emerged twist, while the remaining twist is evacuated along the reconnected arcades. The nature and timing of the features which occur in the simulation do qualititatively reproduce those observed by XRT in the particular event studied in this paper. Moreover, the two-step reconnection process suggests a new consistent and generic model for the formation of anemone regions in the solar corona.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/704/1/485