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CHORUS-MHD Code for Solar and Planetary Magnetohydrodynamics Open Access

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The eruptive solar activities, e.g., solar flares and coronal mass ejections (CMEs),can have a potentially detrimental effect on human space activities or electrical-gridrelated facilities on Earth. One of the well-known disasters on Earth caused by solaractivities happened on March 13, 1989. At 2:44 am EST of that day a severe geomagneticstorm, due to a CME eruption from the Sun, struck Earth. This storm causedthe collapse of the Hydro-Quebec power network due to geomagnetically induced currentsand led to a nine-hour power outage that affected over 6 million people. Whileit is prohibitive for human beings to interfere in solar activities that pose dangers to oursociety it is feasible for us to mitigate the damages and get well prepared before disastershappen. To this end, the comprehensive understanding and accurate predictionof the dynamics of solar activities becomes essential.As of today, two pioneering approaches, helioseismology, and numerical simulations, have been mainly used to study solar activities. Helioseismology is the disciplineof studying the solar structure and dynamics via observing waves and oscillationstraveling towards the solar surface. On the other hand, numerical simulations utilizeaccurate physical models and numerical schemes to simulate solar activities on massivelyparallel computers. Numerical simulations have the advantage of unravelingall essential physics, including magnetic fields, and providing important insights intothe physical processes of the interior of the Sun. Regardless of the fact that numericalsimulations have been seen as a complement tool of helioseismology and alreadycontributed to many meaningful findings in astrophysics, numerical simulations arestill facing challenging problems. One primary challenge is posed by the inherent natureof multi-scale, density-and temperature-stratied flow structures in astrophysics.The other one is due to the geometrical difficulties in representing the whole sphere or spherical shell with structured meshes.The goal of this dissertation research is to make contributions to tackling aforementionedproblems faced by numerical simulations for solar and planetary magnetohydrodynamics(MHD) via developing a high-order, unstructured-grid, robust, andmassively parallel computational framework, CHORUS-MHD. Throughout the developmentof code CHORUS-MHD particular objectives have been set and progresshas been made: (1) in order to capture multi-scale physics precisely and effciently,an adaptive mesh refinement(AMR) method with local time stepping scheme is developedbased on the high-order flux reconstruction (FR) method; (2) a modifiedversion of artificial resistivity technique is proposed for the FR method to suppressand alleviate spurious oscillations near discontinuities; (3) an innovative partitioneddivergence cleaning approach for divergence of magnetic field error is proposed,which has sub-iterative cleaning ability so that divergence B error can be reducedrepeatedly; (4) a characteristic-based boundary condition (CBC) for MHD simulationson computational domains with reduced sizes is proposed. The implementationof CBC on FR method is described in detail for the first time. furthermore, the CBCis successfully applied to simulate magnetic reconnections; (5) 3D, parallel CHORUSMHDis developed. The speedup test shows CHORUS-MHD has great performanceon massively parallel computers. A new solar-like dynamo benchmark is proposed andsimulated by CHORUS-MHD demonstrating CHORUS-MHD's ability to handlecomplex turbulent MHD flows in the solar convection zone.

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