scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
The writhe of helical structures in the solar corona
Török Tibor 1 , Berger Mitchell 2 , Kliem Bernhard 3
1 2 3
LESIA, Observatoire de Paris, France, University of Exeter, United Kingdom, MSSL, University
College London, United Kingdom
Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope
topology, it consists of twist and writhe helicity. Despite the common occurrence of helical
structures in the solar atmosphere, little is known about how their shape relates to the writhe,
which fraction of helicity is contained in writhe, and how much helicity is exchanged between
twist and writhe when such structures erupt. Here we present a quantitative investigation of
these questions relevant for coronal flux ropes. The decomposition of the writhe of a curve
into local and nonlocal components greatly facilitates its computation. We use it to study the
relation between writhe and projected S shape of helical curves and to measure writhe and
twist in numerical simulations of flux rope instabilities. The results are discussed with regard
to sigmoids, stable and eruptive filaments, and coronal mass ejections (CMEs).