ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model I-Model B-Model O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Model B-Model B-Model I-Model O O B-Citation I-Citation I-Citation O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O B-Citation I-Citation O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O B-Model I-Model O O O O B-CelestialObject O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: to a symmetry property of the solution to the transfer equation. To solve this problem, some specific ‘disambiguation’ techniques have been developed. The authors point to one special case where the ambiguity is resolved by the data when combined with knowledge of the state of excitation of the radiating atoms. A purely spectroscopic disambiguation method has also been devised (Landi Degl’innocenti Bommier 1993 ) based on the observation of the Stokes parameter profiles in resonance lines originating from transitions between polarized atomic levels . In this case, the radially streaming radiation from the solar atmosphere introduces a ‘symmetry breaking’ in the physical conditions that allows one, in some cases, to recover the magnetic field vector without ambiguity. The problem remains, even here, that one must know the state of atomic populations of the Zeeman-split M states within the atomic levels. Such conditions exist only for particular radiative transitions. Most polarimetry is performed on photospheric lines formed where collisions tend to enforce equality of M-state populations within local thermodynamic equilibrium (LTE) levels, negating the possibility of any atomic polarization and of symmetry breaking through the radiation field. More worrying, the ‘disambiguation’ methods inflict prior assumptions on solutions to produce ‘inverted’ data compatible with both the assumptions and the data themselves. Especially worrisome are studies seeking to minimize part of the energy of a system, and/or those seeking some kind of minimal discontinuity in the magnetic structure sampled at the photosphere. Such constraints cannot be theoretically supported, the latter, for example, explicitly reject classes of solutions available to magnetohydrodynamics (MHD). ‘Weak’ MHD solutions (e.g. Courant Hilbert 1962 ) exist under conditions encountered on the Sun. Weak solutions solve integral forms of the governing equations in which discontinuities are permitted. Such phenomena not only are expected to pervade the Sun’s atmosphere, but they are expected to harbor much of the free energy in the form of current sheets (e.g. Parker 1972 ; Parker 1994 ). It is precisely this free energy that is so important to the dynamic changes in radiation, particles, and magnetic fields ejected from the Sun. Rapid reconnection associated with current sheets are important for the operation of the large-scale solar dynamo. Recent work has re-assessed the disambiguation problem using ‘realistic’ MHD model calculations of the solar atmosphere, in a hare-and-hound exercise (Fleishman et al. 2017 ). Both successes and failures were found by the authors, conditions within strongly magnetized regions being more reliable than weaker regions. But such methods can never replace more observationally constrained methods, such as those proposed here. They remain dependent on the reality of models, and upon the essential assumptions of the ‘disambiguation’ methods used. The ambiguities