caa a22 4500 445346701 CHVBK 20180317142831.0 cr unu---uuuuu 170323e20110401xx s 000 0 eng 10.1007/s11207-011-9713-x doi (NATIONALLICENCE)springer-10.1007/s11207-011-9713-x Nonlinear Force-Free Reconstruction of the Global Solar Magnetic Field: Methodology [Elektronische Daten] [I. Contopoulos, C. Kalapotharakos, M. Georgoulis] We present a novel numerical method that allows the calculation of nonlinear force-free magnetostatic solutions above a boundary surface on which only the distribution of the normal magnetic field component is given. The method relies on the theory of force-free electrodynamics and applies directly to the reconstruction of the solar coronal magnetic field for a given distribution of the photospheric radial field component. The method works as follows: we start with any initial magnetostatic global field configuration (e.g. zero, dipole), and along the boundary surface we create an evolving distribution of tangential (horizontal) electric fields that, via Faraday's equation, give rise to a respective normal-field distribution approaching asymptotically the target distribution. At the same time, these electric fields are used as boundary condition to numerically evolve the resulting electromagnetic field above the boundary surface, modeled as a thin ideal plasma with non-reflecting, perfectly absorbing outer boundaries. The simulation relaxes to a nonlinear force-free configuration that satisfies the given normal-field distribution on the boundary. This is different from existing methods relying on a fixed boundary condition - the boundary evolves toward the a priori given one, at the same time evolving the three-dimensional field solution above it. Moreover, this is the first time that a nonlinear force-free solution is reached by using only the normal field component on the boundary. This solution is not unique, but it depends on the initial magnetic field configuration and on the evolutionary course along the boundary surface. To our knowledge, this is the first time that the formalism of force-free electrodynamics, used very successfully in other astrophysical contexts, is applied to the global solar magnetic field. Springer Science+Business Media B.V., 2011 Active regions, magnetic fields nationallicence Magnetic fields, corona nationallicence Contopoulos I. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut Kalapotharakos C. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut Georgoulis M. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut Solar Physics Springer Netherlands 269/2(2011-04-01), 351-365 0038-0938 269:2<351 2011 269 11207 https://doi.org/10.1007/s11207-011-9713-x text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11207-011-9713-x text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Contopoulos I. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut NATIONALLICENCE 700 1- Kalapotharakos C. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut NATIONALLICENCE 700 1- Georgoulis M. Research Center for Astronomy and Applied Mathematics (RCAAM), Academy of Athens, 4 Soranou Efessiou Str., 11527, Athens, Greece aut NATIONALLICENCE 773 0- Solar Physics Springer Netherlands 269/2(2011-04-01), 351-365 0038-0938 269:2<351 2011 269 11207 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer