Externally Driven Magnetic Reconnection

Abstract

Some of the important findings obtained by recent numerical simulations of an externally driven magnetic reconnection are reviewed. One of them is the preferential generation of strong streaming of plasma along the plasma sheet boundary (owing to pressure gradient along the magnetic field) in agreement with recent satellite observations. Examination of the energy balance between the magnetic energy and the plasma kinetic energy reveals that a substantial part of the stored magnetic energy is swiftly converted into the plasma bulk flow. It is found that the strength of plasma stream is largely dependent on the condition of the downstream region (field reversal region). Specifically, the streaming velocity becomes as high as the Alfvén speed when the downstream region is unbounded and plasmas can expand freely outward. When the downstream region is bounded, or X-type neutral points are spatially periodic, like periodic tearing modes, the acceleration is weak. This indicates that the external flow can play a crucial role in the rapid conversion of energy as observed, for example, in substorms.