A Practical Approach to Coronal Magnetic Field Extrapolation Based on the Principle of Minimum Dissipation Rate

We present a newly developed approach to solar coronal magnetic field extrapolation from vector magnetograms, based on the Principle of Minimum Dissipation Rate (MDR). The MDR system was derived from a variational problem that is more suitable for an open and externally driven system, like the solar corona. The resulting magnetic field equation is more general than force-free. Its solution can be expressed as the superposition of two linear (constant-$\alpha$) force-free fields (LFFFs) with distinct $\alpha$ parameters, and one potential field. Thus the original extrapolation problem is decomposed into three LFFF extrapolations, utilizing boundary data. The full MDR-based approach requires two layers of vector magnetograph measurements on solar surface, while a slightly modified practical approach only requires one. We test both approaches against 3D MHD simulation data in a finite volume. Both yield quantitatively good results. The errors in the magnetic energy estimate are within a few percents. In particular, the main features of relatively strong perpendicular current density structures, representative of the non-force freeness of the solution, are well recovered.
Comment: submitted to ApJ