Polarity relevance in flux-rope trajectory deflections triggered by coronal holes

Abstract

Context. Many observations suggest that coronal holes (CHs) are capable of deviating the trajectory of coronal mass ejections (CMEs) away from them. However, for some peculiar events, the eruption has been reported to be initially pulled towards the CH and then away from it. Aims. We study the interaction between flux ropes (FRs) and CHs by means of numerical simulations, with the ultimate goal being to understand how CHs can deviate erupting CMEs/FRs from purely radial trajectories. Methods. We perform 2.5D magnetohydrodynamical numerical simulations of FRs and CHs interacting under different relative polarity configurations. In addition, we reconstruct the 3D trajectory and magnetic environment of a particular event seen by the STEREO spacecraft on 30 April 2012, whose trajectory initially departed from the radial direction toward the CH but later moved away from it. Results. The numerical simulations indicate that at low coronal heights, depending on the relative magnetic field polarity between FR and CH, the initial deflection is attractive, that is, the FR moves towards the CH (case of anti-aligned polarities) or repulsive, where the FR moves away from the CH (case of aligned polarities). This is likely due to the formation of vanishing magnetic field regions or null points located between the FR and CH (case of anti-aligned polarities) or at the other side of the FR (case of aligned polarities). The analysed observational event shows a double-deflection compatible with an anti-aligned configuration of magnetic polarities, which is supported by SDO observations. We successfully reproduce the double deflection of the observed event by means of a numerical simulation.