Abstract
Abstract During its first solar encounter, the Parker Solar Probe (PSP) acquired unprecedented up-close imaging of a small coronal mass ejection (CME) propagating in the forming slow solar wind. The CME originated as a cavity imaged in extreme ultraviolet that moved very slowly (<50 km s−1) to 3–5 solar radii (R ⊙), where it then accelerated to supersonic speeds. We present a new model of an erupting flux rope (FR) that computes the forces acting on its expansion with a computation of its internal magnetic field in three dimensions. The latter is accomplished by solving the Grad–Shafranov equation inside two-dimensional cross sections of the FR. We use this model to interpret the kinematic evolution and morphology of the CME imaged by PSP. We investigate the relative role of toroidal forces, momentum coupling, and buoyancy for different assumptions on the initial properties of the CME. The best agreement between the dynamic evolution of the observed and simulated FR is obtained by modeling the two-phase eruption process as the result of two episodes of poloidal flux injection. Each episode, possibly induced by magnetic reconnection, boosted the toroidal forces accelerating the FR out of the corona. We also find that the drag induced by the accelerating solar wind could account for about half of the acceleration experienced by the FR. We use the model to interpret the presence of a small dark cavity, clearly imaged by PSP deep inside the CME, as a low-density region dominated by its strong axial magnetic fields.
Highlights
The solar atmosphere continually releases coronal material and twisted magnetic fields in the form of coronal mass ejections (CMEs)
We study a number of processes that can influence the emergence of the CME including the torus instability, gravitational buoyancy, and the drag force induced by the background solar wind
The 3D-Eruptive Flux Rope (EFR) model presented is a modification of the Chen (1996) model that computes, from the magnetostatic equations, the toroidal forces acting on a slender flux rope
Summary
The solar atmosphere continually releases coronal material and twisted magnetic fields in the form of coronal mass ejections (CMEs). The multipoint STEREO mission has definitely validated the croissant-shaped structure of magnetic FRs (Thernisien et al 2009) for at least a subset of CMEs, with an occasional good correspondence found between FR orientations inferred in simultaneous in situ measurements and white-light imaging (Möstl et al 2009; Rouillard et al 2010; Wood et al 2010) This important step has fundamental implications for our understanding of the dynamic evolution of this subset of CMEs. the difficulties in the more comprehensive analysis by Wood et al (2017) either challenge the idea that all FRs have a croissant-shaped structure, or alternatively, challenge our current methodology to infer the 3D topology of magnetic fields from either imagery or in situ data. We study a number of processes that can influence the emergence of the CME including the torus instability, gravitational buoyancy, and the drag force induced by the background solar wind
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