The violent disruption of the coronal magnetic field is often observed to be
restricted to the low corona, appearing as a confined eruption. The possible
causes of the confinement remain elusive. Here, we model the eruption of a
magnetic flux rope in a quadrupolar active region, with the parameters set such
that magnetic X-lines exist both below and above the rope. This facilitates the
onset of magnetic reconnection in either place but with partly opposing effects
on the eruption. The lower reconnection initially adds poloidal flux to the
rope, increasing the upward hoop force and supporting the rise of the rope.
However, when the flux of the magnetic side lobes enters the lower
reconnection, the flux rope is found to separate from the reconnection site and
the flux accumulation ceases. At the same time, the upper reconnection begins
to reduce the poloidal flux of the rope, decreasing its hoop force; eventually
this cuts the rope completely. The relative weight of the two reconnection
processes is varied in the model, and it is found that their combined effect
and the tension force of the overlying field confine the eruption if the flux
ratio of the outer to the inner polarities exceeds a threshold, which is about
1.3 for our Cartesian box and chosen parameters. We hence propose that external
reconnection between an erupting flux rope and overlying flux can play a vital
role in confining eruptions.Comment: submitted to ApJ Letters that has addressed the referee repor