Three-Dimensional Magnetic Field Topology of Giant Solar Filament
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Date
2018-06-03
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Addis Ababa University
Abstract
Solar filaments are intriguing structures suspended in the solar corona at heights up
to 100Mm above the chromosphere, but they are made of chromospheric material
which is one hundred times cooler and denser than the coronal material, indicating
that they are thermally and pressure isolated from the surrounding environment.
Studying filaments’ topological magnetic field structures, magnetic energy
and electric current density is crucial to know its stability, because unstable conditions
can result in explosive events: flare and coronal mass ejection (CME). All
the studies in the area are limited to the small scale filaments near to the size of
sunspot. This study is the first to use non-linear force-free field (NLFFF) model in
spherical geometry to study a gain filament (with length more than 800Mm) along
polarity inversion line (PIL) where it is in weak-field region (with photospheric field
region of _ 500G). Moreover, the non-linear force-free extrapolation code take uncertainties
in to account in the photospheric field data which occur due to noise,
incomplete inversions or azimuth resolving techniques.
Both potential field and nonlinear force-free coronal magnetic field modeling
methods are applied with preprocessing of photospheric full-disk vector magnetograms
from the Helioseismic and Magnetic Imager (HMI) of solar dynamics observatory
(SDO) and the Vector Spectromagnetograph (VSM) of the Synoptic Optical
Long-term Investigations of the Sun (SOLIS) using the optimization procedure
to full-disk vector magnetograms in spherical geometry is carried-out to make the
boundary data more consistent with the force-free principle. In this process the
pressure gradient and gravity are neglected, and only Lorentz force is considered.
However, in solar corona for the force-free condition the Lorentz force is zero,where
the current density is parallel to the magnetic field.
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Topological magnetic field structure of the filament is resulted from sheared arcades
over the PIL. The magnetic field lines obtained from non-linear force-free
extrapolation based on HMI and VSM data have good agreement though they have
different structures with the magnetic field lines from potential field source surface
(PFSS) model. The non-linear force-free extrapolation based on HMI data have
greater total magnetic energy, free magnetic energy, and surface electric current
density compared to the one from VSM data.
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Keywords
Field Topology, Giant Solar Filament, Magnetic Field