Abstract
Solar eruptions are spectacular magnetic explosions in the Sun’s corona, and how they are initiated remains unclear. Prevailing theories often rely on special magnetic topologies that may not generally exist in the pre-eruption source region of corona. Here, using fully three-dimensional magnetohydrodynamic simulations with high accuracy, we show that solar eruptions can be initiated in a single bipolar configuration with no additional special topology. Through photospheric shearing motion alone, an electric current sheet forms in the highly sheared core field of the magnetic arcade during its quasi-static evolution. Once magnetic reconnection sets in, the whole arcade is expelled impulsively, forming a fast-expanding twisted flux rope with a highly turbulent reconnecting region underneath. The simplicity and efficacy of this scenario argue strongly for its fundamental importance in the initiation of solar eruptions.
Highlights
From time to time, the Sun produces eruptive activities, such as solar flares and coronal mass ejections (CMEs)
We have presented a fully 3D MHD simulation of solar eruption produced in a single bipolar magnetic field, encompassing the entire process from the gradual accumulation of magnetic free energy to its sudden release
The simulated initiation process of eruption bears the major characteristic features of eruptive flares that are associated with CMEs, such as the formation of coronal sigmoid, the transition from slow rise to fast acceleration of coronal loop, the elongation and separation motions of double flare ribbons (Methods A.9), the growth of a flaring cusp structure, as well as the escape and expansion of a plasmoid, which evolves into a coherent magnetic flux rope (MFR) driving a shock ahead
Summary
The Sun produces eruptive activities, such as solar flares and coronal mass ejections (CMEs). The coronal magnetic field is line-tied at the solar surface (i.e., the photosphere), and is continuously but rather slowly stressed by motions at the photosphere (such as surface shear and rotational flows) that could last for a few hours or even days, during which magnetic free energy accumulates. If the overlying flux is not too strong, the eruptive magnetic field can successfully eject into the heliosphere, forming a CME. Otherwise, it fails to escape, resulting in a confined flare or failed eruption
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