Predicting Solar Eruptions More Precisely

In 2014, researchers3 showed that a characteristic structure, an entanglement of magnetic force lines twisted together like a hemp rope, gradually appears in the days preceding a solar flare. However, until recently then they had only observed this rope in eruptions that ejected bubbles of plasma. In this new study, the researchers studied other types of flare, the models of which are still being debated, by undertaking a more thorough analysis of the solar corona, a region where the Sun’s atmosphere is so thin and hot that it is difficult to measure the solar magnetic field there. They did this by measuring stronger magnetic field at the surface of the Sun, and then using these data to reconstruct what was happening in the solar corona(4).

They applied this method to a major flare that developed over a few hours on October 24, 2014. They showed that, in the hours before the eruption, the evolving rope was confined within a multilayer magnetic ‘cage’. Using evolutionary models running on supercomputer, they showed that the rope had insufficient energy to break through all the layers of the cage, making the ejection of a magnetic bubble impossible. Despite this, the high twist of the rope triggered an instability and the partial destruction of the cage, causing a powerful emission of radiation that led to disruptions on Earth.

Thanks to their method, which makes it possible to monitor the processes taking place in the last few hours leading up to a flare, the researchers have developed a model able to predict the maximum energy that can be released from the region of the Sun concerned. The model showed that for the 2014 eruption, a huge ejection of plasma would have occurred if the cage had been less resistant.

1 At the Centre de Physique Théorique (CNRS/École Polytechnique/), the Laboratoire d’Astrophysique, Instrumentation, Modélisation (CNRS/CEA/Université Paris Diderot), the Laboratoire de Physique Théorique de la Matière Condensée (CNRS/Sorbonne Université) and the Gamma3 team at INRIA.
2 See the press release: ‘Understanding and predicting solar eruptions’: http://www2.cnrs.fr/en/2467.htm
3 See footnote 2.
4 The data was taken from observation of the Sun’s surface by NASA’s Solar Dynamic Observatory (SDO) mission. The numerical models of the magnetic fields were obtained using supercomputers at IDRIS/CINES and the École Polytechnique.

Contacts and sources:
CNRS (Délégation Paris Michel-Ange)