A 2 1/2-dimensional fully electromagnetic particle simulation code is used to study the temporal evolution of a plasma magnetized by a dipole embedded in a uniform magnetic field, as the direction of the uniform field reverses direction. The magnetic field topology is observed to change from an open to a closed configuration. Our simulations show that as the magnetic field reversal propagates into the ambient plasma, a current sheet forms and moves toward the dipole at about the local Alfv¿n speed. The current sheet breaks into filaments, with each filament interacting with the dipole in a process that resembles coalescence, resulting in some particle heating. We find that the resulting magnetic field topology does not depend significantly on the initial plasma &bgr; for 1.0>&bgr;>0.05.