  The trajectories of coronal mass ejections (CMEs) are often seen to
substantially deviate from a purely radial propagation direction. Such
deviations occur predominantly in the corona and have been attributed to
"channeling" or deflection of the eruptive flux by asymmetric ambient magnetic
fields. Here, we investigate an additional mechanism that does not require any
asymmetry of the pre-eruptive ambient field. Using magnetohydrodynamic
numerical simulations, we show that the trajectory of CMEs through the solar
corona can significantly deviate from a radial direction when propagation takes
place in a unipolar radial field. We demonstrate that the deviation is most
prominent below ~15 solar radii and can be attributed to an "effective IxB
force" that arises from the intrusion of a magnetic flux rope with a net axial
electric current into a unipolar background field. These results are important
for predictions of CME trajectories in the context of space weather forecasts,
as well as for reaching a deeper understanding of the fundamental physics
underlying CME interactions with the ambient fields in the extended solar
corona.
