Magnetically Induced Current Piston for Generating Extreme-ultraviolet Fronts in the Solar Corona

Abstract

Single-pulse, globally propagating coronal fronts, called Extreme-ultraviolet (EUV) waves, were first observed in 1995 by the Extreme-ultraviolet Imaging Telescope and every observed EUV wave since has been associated with a coronal mass ejection (CME). The physical mechanism underlying these waves has been debated for two decades with wave or pseudo-wave theories being advocated. We propose a hybrid model where EUV waves are compressional fronts driven by a reverse electric current layer induced by the time-dependent CME core current. The reverse current layer flows in a direction opposite to the CME core current and is an eddy current layer necessary to maintain magnetic flux conservation above the layer. Repelled by the core current, the reverse current layer accelerates upward so it acts as a piston that drives a compressional perturbation in the coronal regions above. Given a sufficiently fast piston speed, the compressional perturbation becomes a shock that separates from the piston when the piston slows down. Since the model relates the motion of the EUV front to CME properties, the model provides a bound for the core current of an erupting CME. The model is supported and motivated by detailed results from both laboratory experiments and ideal 3D magnetohydrodynamic simulations. Overlaps and differences with other models and spacecraft observations are discussed.

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“…Wongwaitayakornkul et al. (2019) have shown that this piston motion can drive a shock wave in the background plasma and have proposed this CME‐driven shock as an explanation for the EUV waves (Long et al., 2017) that are often seen in association with CMEs.…”

“…These models are not only relevant to solar physics, but also to magnetospheric physics and to astrophysics which can have similar physics but at very different scales from the lab or the Sun. Examples of such theoretical models are the following: A model showing why flux ropes tend to be collimated (Bellan, 2003) A model for how accretion disks and astrophysical jets form a complete electric circuit that transfers angular momentum in a conservative way much like a generator transfers angular momentum via wires to a distant motor (Bellan, 2016a, 2018d) A model providing a time‐dependent analytic solution for an astrophysical jet (Bellan, 2020) A model for how energetic particles are created in the presence of sub‐Dreicer electric fields (Marshall & Bellan, 2019) A model providing an intuitive explanation for fast collisionless magnetic reconnection (Yoon & Bellan, 2017, 2019a) in the electron MHD context, that is, the context where the timescale is so fast that ions can be considered stationary, and the reconnection length scale is short compared to the ion skin depth, so Hall terms and electron inertia are important. A model showing that ions experience fast stochastic heating during fast collisionless reconnection (Yoon & Bellan, 2018, 2019b) A model showing how the reverse current associated with coronal mass ejection drives EUV fronts in the solar corona (Wongwaitayakornkul et al., 2019) …”