Pi 2 pulsations: High latitude results

A review of recent experimental results from studies of high latitude Pi 2 pulsations indicates that these pulsations are fundamentally related to the initiation of the auroral breakup and substorm. At high latitudes, the Pi 2's show their peak intensities in the region where the breakup begins and appear to remain in this region after the breakup has spread poleward. In addition, the Pi 2's occur simultaneously with, or before all other ionospheric phenomena associated with the breakup. The field aligned and ionospheric currents associated with the Pi 2 resemble those of a typical substorm, but the ionospheric currents are phase shifted compared to the field aligned current. The periodic oscillations of the Pi 2's are probably caused by a reflection of the initial field aligned current pulse from the auroral ionosphere. This pulse is trapped on dipolar field lines leading to multiple reflections from North and South auroral ionospheres.