Extrapolation of Three-dimensional Magnetic Field Structure in Flare-productive Active Regions with Different Initial Conditions

The nonlinear force-free field (NLFFF) modeling has been extensively used as a tool to infer three-dimensional (3D) magnetic field structure. In this study, the dependency of the NLFFF calculation with respect to the initial guess of the 3D magnetic field is investigated. While major part of the previous studies used potential field as the initial guess in the NLFFF modeling, we adopt the linear force-free fields with different constant force-free alpha as the initial guesses. This method enables us to investigate how unique the magnetic field obtained by the NLFFF extrapolation with respect to the initial guess is. The dependence of the initial condition of the NLFFF extrapolation is smaller in the strong magnetic field region. Therefore, the magnetic field at the lower height ($< 10$ Mm) tends to be less affected by the initial condition (correlation coefficient C>0.9 with different initial condition), although the Lorentz force is concentrated at the lower height.

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