Theories of Magnetic Field Annihilation

A critical summary is given of the various theories for magnetic field annihilation. In addition a new exact three-dimensional solution of the magnetohydrodynamic equations is described. It represents the annihilation of two sets of magnetic flux as they are brought together by a stagnation point flow; situated in the regions x > 0 and x < 0, the two fields are not simply antiparallel, but may be inclined at any angle θ parallel to the plane x = 0. The resulting electric field as a function of θ is estimated; for axisymmetric flow the field is proportional to sin-½θ and for non-axisymmetric flow it does not necessarily increase with θ.