Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison |
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Authors: | A R Yeates D H Mackay A A van Ballegooijen |
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Institution: | (1) School of Mathematics and Statistics, University of St Andrews, Fife, KY16 9SS, Scotland;(2) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA |
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Abstract: | This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric
and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation
is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field
evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary
conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active
regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose
the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality
for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or
helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion
of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal
field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It
highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different
times. This has significant consequences for future modelling such as that related to the origin and development of coronal
mass ejections. |
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Keywords: | Magnetic fields: corona Prominences: magnetic field Helicity: magnetic |
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