Blazej Kuzma, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Michaela Brchnelova, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Barbara Perri, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Tinatin Baratashvili, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Fan Zhang, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Andrea Lani, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium; Stefaan Poedts, Centre for Mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Belgium and Institute of Physics, University of Maria Curie-Sklodowska, Poland
Keywords: solar wind, space weather, solar corona, heliosphere, methods: numerical
Abstract:
We developed a novel global coronal model based on the COOLFluiD code. The steady-state model is predetermined by magnetograms set as boundary conditions, while inside the numerical domain of our simulation the corona is described by the set of MHD equations. This set of equations is solved with use of implicit solver on an unstructured grid. Our code has passed a set of benchmark tests and proved its accuracy for simple dipole / quadrupole solutions as well as for a wide range of magnetograms, both during solar minimum and solar maximum. With various numerical optimization techniques and an adaptive CFL step we decreased the computation time while maintaining the high robustness and reliability. Finally, we coupled the obtained results with a heliospheric wind model of EUHFORIA 2.0 space weather forecast to show its forecast abilities. All this leads to an accurate MHD solution obtained within only a few hours of computation, which is crucial for space weather forecast systems.
Here we present some numerically obtained results for 2008, 2015, 2017 and 2019 magnetograms (CR 2072, CR 2161, CR 2194, CR 2219). These magnetograms were chosen to represent a variety of stages of solar activity, from minimum to maximum, with each of them corresponding to a particular solar eclipse, to allow us the direct comparison of simulations with observed coronal structures. Following the commonly used procedure the input raw / original MDI and HMI magnetograms are pre-processed by projection on spherical harmonics and a selection of a maximum frequency for the reconstruction. This is equivalent to a smoothing of the map and results in removal of the small, intense magnetic structures on the solar surface. The latter are in fact numerically more challenging, while their contribution to the overall structure of the solar wind at 0.1 AU and the large-scale coronal magnetic fields has not been thoroughly investigated yet. With several maps and several levels of accuracy of reconstruction we address this problem and show the map resolution and pre-processing impact on accuracy of the numerical results. This is especially important for computationally challenging maximum-activity magnetograms which require significant pre-processing for stability and computational speed purposes.
To verify our numerical results we use a validation scheme proposed by Wegener et al. 2022 (from less to more sophisticated methods, i.e. visual classification, feature matching, streamer direction and width, brute force matching, topology classification). We investigate the predicted within our simulations distribution of magnetic structures and the obtained coronal magnetic field topology. The detailed comparison with observations reveals that our model recreates relevant features such as the position and shape of the streamers (by comparison with white-light images), the coronal holes (by comparison with EUV images) and the current sheet (by comparison with WSA model at 0.1 AU). We conclude that an unprecedented combination of accuracy, computation speed and robustness is accomplished at this stage, with possible improvement in a foreseeable perspective. Our results also show that the final solution is still very sensitive to the map chosen and its pre-processing, especially for solar maximum-activity cases.
Date of Conference: September 27-20, 2022
Track: Atmospherics/Space Weather