Abstract
The effects of background plasma sheet boundary conditions on the downward current region potential structures are investigated using FAST observations of both ionospheric and plasma sheet populations. Precipitating plasma sheet electrons are observed to partially control the magnitude of the potential drop consistent with theories of charge‐neutrality requirements throughout ionospheric and magnetospheric regions. This leads to a new empirical model of a downward current region (DCR) current‐voltage relation for U‐shaped events. Hot plasma sheet ions are observed to play an important role in reducing the variability of the potential drop, possibly by acting as a sink or buffer for free energy caused by the resulting energetic upward electron beams. The statistical studies of boundary conditions in the auroral downward current region in this and our companion paper show that both ionospheric and magnetospheric conditions appear to regulate the DCR potential structures observed at FAST altitudes. The initiation of downward current region potentials seems to be influenced mainly by low‐altitude ionospheric conditions. Once the U‐shaped potential structure is formed, the effects of the ionospheric influences may be relaxed and modulated by effects from magnetospheric conditions.
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