Three-dimensional separator reconnection - How does it occur?

In two dimensions magnetic energy release takes place at locations where th e magnetic field strength becomes zero and has an x-point topology. The x-p oint topology can collapse into two y-points connected by a current sheet w hen the advection of magnetic flux into the x-point is larger than the diss ipation of magnetic flux at the x-point. In three dimensions magnetic field s may also contain singularities in the form of three-dimensional null poin ts. Three-dimensional nulls are created in pairs and are therefore, at leas t in the initial stages, always connected by at least one field line - the separator. The separator line is defined by the intersection of the fan pla nes of the two nulls. In the plane perpendicular to a single separator the field line topology locally has a two dimensional x-point structure. Using a numerical approach we find that the collapse of the separator can be init iated at the two nulls by a velocity shear across the fan plane. It is foun d that for a current concentration to connect the two nulls along the separ ator, the current sheet can only obtain two different orientations relative to the field line structure of the nulls. The sheet has to have an orienta tion midway between the fan plane and the spine axis of each null. As part of this process the spine axes are found to lose their identity by transfor ming into an integrated part of the separator surfaces that divide space in to four magnetically independent regions around the current sheet.