Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison

TL;DR

This study uses global-scale simulations of the solar magnetic field over six months to analyze filament chirality, demonstrating that helicity injection and long-term evolution are key to matching observed filament patterns.

Contribution

It introduces a continuous, long-term coronal evolution model that accurately reproduces filament chirality, emphasizing the role of helicity transport and memory in the solar corona.

Findings

Model reproduces 96% of filament chirality when active-region helicity matches observations.

Long-term evolution enhances the accuracy of filament chirality predictions.

Helicity transport from low to high latitudes is crucial for coronal field development.

Abstract

The hemispheric pattern of solar filaments is considered using newly-developed simulations of the real photospheric and 3D coronal magnetic fields over a 6-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.