The change of magnetospheric configuration due to cross-tail current disruption and its possible relation to the appearance of Θ-aurora

Closed "dipole-like" field lines appear in the central portion of the magnetotail when the crosstail electric current is disrupted and diverted into the ionosphere. The field lines remain strongly stretched to antisunward direction at the flanks of the magnetqsphere outside the region of current disruption, resulting in a tail-like configuration. We suggest that Such a configuration is responsible for Θ-aurora production. The plasma sheet is bifurcated as plasma flows freely from the plasma sheet to the polar cap along "dipole-like" field lines appearing due to cross-tail current disruption. For this model the field-aligned current should be directed into the ionosphere at the dawn side of the transpolar arc and out of the ionosphere at the dusk side.