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

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 parts of the previous studies used the potential field as the initial guess in NLFFF modeling, we adopt linear force-free fields with different constant force-free alpha as the initial guesses. This method enables us to investigate the uniqueness of the magnetic field obtained by the NLFFF extrapolation with respect to the initial guess. The dependence of the initial conditions on NLFFF extrapolation is smaller in the strong magnetic field region. Therefore, the magnetic field at lower heights (<10 Mm) tends to be less affected by the initial conditions (correlation coefficient C > 0.9 with different initial conditions); although, the Lorentz force is concentrated at lower heights.