Neutral sheets

With the growth of recognition of the importance of neutral sheets, the complexity of the subject has become apparent. Although the crucial problem concerns the vicinity of a neutral line, where the normal componentB _z may be neglected, only a small fraction of satellite crossings can be expected in such a small region. The breakdown of the problem will be discussed and possible trajectories described for particles entering from either the lobes or the magnetosheath. In each region a self-consistent problem must be solved for the electrostatic field and it is noted that this can drive field aligned currents to the ionosphere. High frequency instabilities will also be discussed and seem capable of causing the explosive onset of substorms.