TY  - JOUR
A1  - Kliem, Bernhard
A1  - Seehafer, Norbert
T1  - Helicity shedding by flux rope ejection
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We quantitatively address the conjecture that magnetic helicity must be shed from the Sun by eruptions launching coronal mass ejections in order to limit its accumulation in each hemisphere. By varying the ratio of guide and strapping field and the flux rope twist in a parametric simulation study of flux rope ejection from approximately marginally stable force-free equilibria, 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 over 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. Torus-unstable configurations with subcritical twist and without a guide field shed up to about two-thirds of the initial helicity, while a highly twisted, kink-unstable configuration sheds only about one-quarter. The parametric study also yields stable force-free flux rope equilibria up to a total flux-normalized helicity of 0.25, with a ratio of self- to total helicity of 0.32 and a ratio of flux rope to external poloidal flux of 0.94. These results numerically demonstrate the conjecture of helicity shedding by coronal mass ejections and provide a first account of its parametric dependence. Both self- and mutual helicity are shed significantly; this reduces the total initial helicity by a fraction of ∼0.4--0.65 for typical source region parameters.
KW  - instabilities
KW  - magnetic fields
KW  - magnetohydrodynamics (MHD)
KW  - Sun
KW  - corona
KW  - coronal mass ejections (CMEs)
KW  - flares
Y1  - 2022
U6  - https://doi.org/10.1051/0004-6361/202142422
SN  - 0004-6361
SN  - 1432-0746
VL  - 659
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - GEN
A1  - Kliem, Bernhard
A1  - Rust, S.
A1  - Seehafer, Norbert
T1  - Helicity transport in a simulated coronal mass ejection
T2  - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe
N2  - It has been suggested that coronal mass ejections (CMEs) remove the magnetic he-licity of their coronal source region from the Sun. Such removal is often regarded to be necessary due to the hemispheric sign preference of the helicity, which inhibits a simple annihilation by reconnection between volumes of opposite chirality. Here we monitor the relative magnetic he-licity contained in the coronal volume of a simulated flux rope CME, as well as the upward flux of relative helicity through horizontal planes in the simulation box. The unstable and erupting flux rope carries away only a minor part of the initial relative helicity; the major part remains in the volume. This is a consequence of the requirement that the current through an expanding loop must decrease if the magnetic energy of the configuration is to decrease as the loop rises, to provide the kinetic energy of the CME.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 569 
KW  - magnetic fields
KW  - MHD
KW  - coronal mass ejections
KW  - magnetohydrodynamics
KW  - sun
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-412907
SN  - 1866-8372
IS  - 569
SP  - 125
EP  - 128
ER  -