Evolutionary Dynamics of Counterhelical Magnetic Flux Ropes

Abstract Upon interaction, a pair of magnetic flux ropes can merge to form a new pair, each consisting of opposite helicity along their axis. Magnetic helicity along such new structures may annihilate and release the energy of the azimuthal magnetic field. In this study, we model the deformation dynamics of such structures within the solar wind at 1 au. The perturbation front of deformation propagates along the rope axis at approximately the Alfvén speed. However, the process of annihilating 90% of the azimuthal components is much slower and is affected by the screw pitch of the magnetic field. Such a deformation process causes the plasma in the transition region between the two opposite chiralities to spin about the rope axis. The resulting plasma heating is discussed accordingly. Our results provide insights for estimating the lifetimes of such flux ropes, facilitating observational efforts to identify them. This process may also apply to the behavior of magnetic flux ropes in other space and astronomical plasma environments.