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EP: Fachverband Extraterrestrische Physik

EP 4: Sun and Heliosphere II

EP 4.2: Vortrag

Mittwoch, 1. April 2020, 11:00–11:15, H-HS VIII

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

It has been suggested that coronal mass ejections (CMEs) remove the magnetic helicity of active regions from the Sun. Such removal is often regarded to be necessary due to the hemispheric sign preference of the helicity, which inhibits a complete annihilation by magnetic reconnection between volumes of opposite helicity. We have monitored the relative magnetic helicity contained in the coronal volume of erupting magnetic flux ropes. The torus instability, or a combination of helical kink and torus instability, leads to eruption and ejection of the flux rope, which is a model for CMEs. It is found that the fraction of helicity ejected depends strongly on the characteristics of the initial force-free equilibrium of the flux rope. For a rather strongly twisted, initially kink-unstable flux rope of 2.5 field line turns, which has a relatively large fraction of self-helicity, not only the normalized total initial helicity (< 0.1) but also the ejected helicity (about 30 per cent) are relatively small. For a weakly twisted (solely torus-unstable) flux rope, which has a relatively large fraction of mutual helicity, up to 2/3 of the much higher initial helicity (0.2–0.3) are shed. This supports the conjecture hat helicity shedding by CMEs is an important aspect of the solar magnetism.