SMuK 2021 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 1: Sun and Heliosphere I

EP 1.2: Talk

Monday, August 30, 2021, 11:30–11:45, H7

Helicity Shedding by Flux Rope Ejection — •Bernhard Kliem and Norbert Seehafer — Universität Potsdam, Institut für Physik und Astronomie

It has been suggested that magnetic helicity must be shed from the Sun by coronal mass ejections to limit its accumulation in each hemisphere. However, the efficiency of such helicity shedding and its dependence on source region parameters are not yet known. We perform a parametric simulation study of flux rope ejection from marginally stable force-free equilibria to address these questions. By varying the ratio of guide and strapping field and the flux rope twist, different ratios of self and mutual helicity are set and the onset of the torus or helical kink instability is obtained. The helicity shed is found to vary in a broad range from a minor to a major part of the initial helicity, with self helicity being largely or completely shed and mutual helicity, which makes up the larger part of the initial helicity, being shed only partly, up to a configuration-dependent base level. The torus-unstable configuration without a guide field and with only a relatively weak twist sheds nearly 2/3 of the initial helicity, while the highly twisted, kink-unstable configuration sheds only 1/4. The initial flux-normalized helicity of the former configuration is 0.21, a value presumably not far from the maximum helicity that a stable force-free flux rope equilibrium can contain. These results numerically demonstrate the conjecture of helicity shedding by coronal mass ejections and provide a first account of its parametric dependence.