Evolution of magnetospheric current wedge by the spontaneous fast reconnection model

Abstract

On the basis of the spontaneous fast reconnection model, the underlying physical mechanism of magnetospheric current wedge evolution is studied by magnetohydrodynamic simulations. It is demonstrated that when a three-dimensional magnetic loop top is compressed by the fast reconnection jet, field-aligned currents are suddenly generated by the resulting sheared fields inside the loop; simultaneously, a large-scale current wedge evolves to link, through the field-aligned currents, the sheet current ahead of the magnetic loop to the current in the local loop footpoint of reconnected field lines. In accordance with the current-wedge evolution, the sheet current, which initially flows ahead of the loop top in the middle of the system, is abruptly bifurcated and turns its direction toward the local loop footpoint, where strong currents are concentrated and intensified. Therefore, once the channel for the current wedge is realized, effective energy dissipation occurs, through the channel, in the local region of the loop footpoint connected to the separatrix, which bounds the reconnected field lines and the ambient (prereconnection) field lines.