Comparison of Nonlinear Force-Free Field and Potential Field in the Quiet Sun

Abstract

In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct boundary integral (DBIE), and approximate vertical integration (AVI) methods) are used to study the spatial configuration of magnetic field in the quiet Sun. It is found that differences in the computed field strengths among the three NLFF and potential fields exist in the low layers. However, they tend to disappear as the height increases, and the differences are of the order of 0.1 gauss when the height exceeds ≈ 2000 km above the photosphere. The difference in azimuth angles between each NLFF field model and the potential field is as follows: for the optimization field, it decreases evidently as the height increases; for the DBIE field, it almost stays constant and shows no significant change as the height increases; for the AVI field, it increases slowly as the height increases. Our analysis shows that the reconstructed NLFF fields deviate significantly from the potential field in the quiet Sun.