Analysis of magnetometer and HF radar data suggests that the auroral electrojet associated with
substorm activity comprises two distinct elements, a long lived (>30 minutes) component and a short
lived (<10 minute) intensification which coalesces with the longer lived component.
A detailed inter-comparison between the occurrence of Pi2 and the injection of energetic particles to geostationary orbit has been carried out. These two phenomena are key features used for the identification of substorms.
Recent studies have provided a comprehensive description of the electric field response to the substorm growth phase and expansion phase onset of a relatively simple isolated substorm (|AL| < 250 nT). The growth phases is marked by a significant equatorward motion of the radar backscatter as the auroral oval expands, much greater than usual, but typical for a substorm preceded by a prolonged period (> 12 hours) of magnetic quiescence. At substorm onset a dramatic change occurs and a poleward flow component replaces the equatorward flow that existed prior to onset.
Work is underway to describe the electric field during both the expansion and recovery phases of relatively simple substorms.
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