A critical assessment of nonlinear force-free field modeling
of the solar corona for active region 10953
M. L. DeRosa, C. J. Schrijver et al.
2009, ApJ, 696, 1780
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Abstract
Nonlinear force-free field (NLFFF) models are thought to be viable tools for investigating the structure, dynamics
and evolution of the coronae of solar active regions. In a series of NLFFF modeling studies, we have found that
NLFFF models are successful in application to analytic test cases, and relatively successful when applied to numerically
constructed Sun-like test cases, but they are less successful in application to real solar data. Different NLFFF models
have been found to have markedly different field line configurations and to provide widely varying estimates of the
magnetic free energy in the coronal volume, when applied to solar data. NLFFF models require consistent, forcefree
vector magnetic boundary data. However, vector magnetogram observations sampling the photosphere, which is
dynamic and contains significant Lorentz and buoyancy forces, do not satisfy this requirement, thus creating several
major problems for force-free coronal modeling efforts. In this article, we discuss NLFFF modeling of NOAA Active
Region 10953 using Hinode/SOT-SP, Hinode/XRT, STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the
process illustrate the three such issues we judge to be critical to the success of NLFFF modeling: (1) vector magnetic
field data covering larger areas are needed so that more electric currents associated with the full active regions of interest
are measured, (2) the modeling algorithms need a way to accommodate the various uncertainties in the boundary data,
and (3) a more realistic physical model is needed to approximate the photosphere-to-corona interface in order to better
transform the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of
the corona. We make recommendations for future modeling efforts to overcome these as yet unsolved problems.
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