Deflection of CMEs in Different Background Magnetic Fields

As suggested by Isenberg and Forbes (2007) and demonstrated numerically by Kliem et al. (2012), the Lorentz forces stemming from the interaction of the axial current in an erupting magnetic flux rope (MFR) with an ambient magnetic-field component that has the same orientation as the initial MFR axis leads to a rotation of the top part of the MFR about its rise direction. In principle, the same mechanism can be applied to CMEs that propagate in a unipolar radial field in the corona or inner heliosphere. In such cases, however, the corresponding forces should not lead to a rotation, but to a deflection of the CME front, thereby significantly altering the CME's magnetic orientation. Apart from a brief consideration in Lugaz et al. (2011), such deflections have, to the best of our knowledge, not yet been studied systematically. 

Here we employ three-dimensional (3D) idealized magnetohydrodynamic (MHD) simulations to investigate this effect in background fields of increasing complexity. We first consider a freely expanding toroidal MFR in a uniform background field, as well as the propagation of a compact, line-tied MFR in a unipolar radial field. In both cases, we find significant deflections. We then use a more realistic setup, in which we erupt an MFR from a localized, bipolar source region into a global dipole field and solar wind, which allows for a significant expansion of the MFR before it encounters open field. We perform a parametric study in which we vary the location and magnetic orientation of the source region, as well as the handedness (helicity sign) of the MFR. In this presentation, we discuss the influence of these parameters on the CME trajectory.