A. Malanushenko, C. J. Schrijver, M. L. DeRosa, M. S. Wheatland, S. A. Gilchrist
Presently, many models of the coronal magnetic field rely on photospheric
vector magnetograms but these data have been shown to be problematic as the
sole boundary information for nonlinear force-free field (NLFFF)
extrapolations. Magnetic fields in the corona manifest themselves in
high-energy images (X-rays and EUV) in the shapes of coronal loops, providing
an additional constraint that at present is not used due to the mathematical
complications of incorporating such input into numerical models. Projection
effects and the limited number of usable loops further complicate the use of
coronal information. We develop and test an algorithm to use images showing
coronal loops in the modeling of the solar coronal magnetic field. We first fit
projected field lines with field lines of constant-\als force-free fields to
approximate the three-dimensional distribution of currents in the corona along
a sparse set of trajectories. We then apply a Grad-Rubin-like iterative
technique to obtain a volume-filling nonlinear force-free model of the magnetic
field, modifying method presented in \citet{Wheatland2007}. We thoroughly test
the technique on known analytical and solar-like model magnetic fields
previously used for comparing different extrapolation techniques
\citep{Schrijver2006, Schrijver2008} and compare the results with those
obtained by presently available methods that rely only on the photospheric
data. We conclude that we have developed a functioning method of modeling the
coronal magnetic field by combining the line-of-sight component of photospheric
magnetic field with information from coronal images. Vector magnetograms over
the full or partial photospheric boundary of the numerical domain could
optionally be used.
View original:
http://arxiv.org/abs/1202.5420
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