Sources of field‐aligned currents in the auroral plasma

Data from the Dynamics Explorer 1 High Altitude Plasma Instrument (HAPI) and magnetometer are used to investigate the sources of field‐aligned currents in the nightside auroral zone. It is found that the formula developed by S. Knight predicts the field‐aligned current density fairly accurately in regions where a significant potential drop can be inferred from the HAPI data; there are, however, regions in which the proportionality between potential drop and field‐aligned current does not hold. In particular, we note occurrences of strong upward field‐aligned current associated not with inverted‐V events but instead with supratherrnal bursts. In addition, upward field‐aligned currents are often observed to peak near the edges of inverted‐V events, rather than in the center as would be predicted by Knight.