2018/02/28 by Philippe-A. Bourdin, Bernhard Hofer, Yasuhito Narita · 1 citation
Physics and Astronomy · #astro-ph.SR #physics.plasm-ph
paper · pdf · doi:10.3847/1538-4357/aaae04
published as ApJ, 855:111 (10pp), 2018 · 10 pages, 14 figures, published
arxiv created 2018/05/15 · arxiv updated 2018/05/17
Electromotive force is an essential quantity in dynamo theory. During a coronal mass ejection (CME), magnetic helicity gets decoupled from the Sun and advected into the heliosphere with the solar wind. Eventually, a heliospheric magnetic transient event might pass by a spacecraft, such as the Helios space observatories. Our aim is to investigate the electromotive force, the kinetic helicity effect (α term), the turbulent diffusion (β term) and the cross-helicity effect (γ term) in the inner heliosphere below 1 au. We set up a one-dimensional model of the solar wind velocity and magnetic field for a hypothetic interplanetary CME. Because turbulent structures within the solar wind evolve much slower than this structure needs to pass by the spacecraft, we use a reduced curl operator to compute the current density and vorticity. We test our CME shock-front model against an observed magnetic transient that passes by the Helios-2 spacecraft. At the peak of the fluctuations in this event we find strongly enhanced α, β and γ terms, as well as a strong peak in the total electromotive force. Our method allows us to automatically identify magnetic transient events from any in-situ spacecraft observations that contain magnetic field and plasma velocity data of the solar wind.