CURRENT ACCUMULATION AT A 3-DIMENSIONAL MAGNETIC NULL

The cold, linear, resistive, magnetohydrodynamic (MHD) equations are u sed to study the dynamics of current accumulation at a three-dimension al magnetic null. The particular null under study is axisymmetric abou t its so-called spine axis, allowing a decomposition into azimuthal mo des labeled by mode number m. Analysis shows that the axisymmetric per turbations (m=0) can lead to a current parallel to the spine axis at t he null, while the m=1 mode produces currents orthogonal to the spine axis at the null (in the so-called fan plane). For all the modes with m>1, there is no current accumulation at the null. The dynamic process es involved in producing these currents are revealed using numerical s imulations. In particular, it is found that the m=1 mode leads to moti ons across both the fan plane and the spine axis regardless of whether the initially imposed disturbances are restricted to be across either the fan plane or the spine axis. The m=1 mode efficiently focuses the excess magnetic energy in toward the null, and therefore we consider it to be the prime reconnective mode in three dimensions. In attemptin g to understand magnetic reconnection at a three-dimensional null, it is clearly important to detail the currents that can be produced. This we have done within the framework of the linear theory. We discuss th e implications of these results for reconnection in the solar corona i n the presence of finite-amplitude fields and flows.