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Energy and helicity fluxes in line-tied eruptive simulations

Abstract : Context. Conservation properties of magnetic helicity and energy in the quasi-ideal and low-β solar corona make these two quantities relevant for the study of solar active regions and eruptions. Aims. Based on a decomposition of the magnetic field into potential and nonpotential components, magnetic energy and relative helicity can both also be decomposed into two quantities: potential and free energies, and volume-threading and current-carrying helicities. In this study, we perform a coupled analysis of their behaviors in a set of parametric 3D magnetohydrodynamic (MHD) simulations of solar-like eruptions. Methods. We present the general formulations for the time-varying components of energy and helicity in resistive MHD. We calculated them numerically with a specific gauge, and compared their behaviors in the numerical simulations, which differ from one another by their imposed boundary-driving motions. Thus, we investigated the impact of different active regions surface flows on the development of the energy and helicity-related quantities. Results. Despite general similarities in their overall behaviors, helicities and energies display different evolutions that cannot be explained in a unique framework. While the energy fluxes are similar in all simulations, the physical mechanisms that govern the evolution of the helicities are markedly distinct from one simulation to another: the evolution of volume-threading helicity can be governed by boundary fluxes or helicity transfer, depending on the simulation. Conclusions. The eruption takes place for the same value of the ratio of the current-carrying helicity to the total helicity in all simulations. However, our study highlights that this threshold can be reached in different ways, with different helicity-related processes dominating for different photospheric flows. This means that the details of the pre-eruptive dynamics do not influence the eruption-onset helicity-related threshold. Nevertheless, the helicity-flux dynamics may be more or less efficient in changing the time required to reach the onset of the eruption.
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Submitted on : Wednesday, May 6, 2020 - 12:24:37 PM
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L. Linan, E. Pariat, G. Aulanier, K. Moraitis, G. Valori. Energy and helicity fluxes in line-tied eruptive simulations. Astronomy and Astrophysics - A&A, EDP Sciences, 2020, 636, pp.A41. ⟨10.1051/0004-6361/202037548⟩. ⟨hal-02565261⟩



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