Consequences of current interruption for plasma sheet dynamics

Abstract

A three‐dimensional, fully electromagnetic particle simulation model is used to explore the upper limits to the physical effects which might be produced by the onset of anomalous resistance within the substorm growth phase thin near‐Earth current sheet. This is accomplished by blocking a local portion of the cross‐tail current at regular intervals of ≈2ωpe−1. The blocking leads to an enhancement of the cross‐tail electric field and to the formation of a localized reconnection region. Within the blocking region the in‐plane (xz) current system is dominated by the reconnection Hall currents. On the earthward side of the X line, the Hall currents flow into (out of) the ionosphere at higher (lower) latitude, thus forming a coaxial sheet current system. The field‐aligned currents that originate from the diversion of the cross‐tail current are likewise dominated by the reconnection Hall currents, with the “substorm current wedge” involving only a relatively small fraction of the total field‐aligned current. This study suggests that the sudden onset of a very strong anomalous resistance can, in principle, disrupt the near‐Earth current sheet and produce a diversion of a portion of the cross‐tail current onto an ionospheric closure path. Whether such a current sheet disruption is, in fact, responsible for substorm onset is still unclear.