Nonlinear force-free extrapolations are a common approach to estimate the 3D topology of coronal magnetic fields based on photospheric vector magnetograms. The force-free assumption is a valid approximation at coronal heights. but for the dense plasma conditions in the lower atmosphere. this assumption is not satisfied. https://www.alarecre.com/NHL-Dallas-Stars-Black-Background-iPhone-13-Pro-Max-MagSafe-Case-p96318/