Multiple auroral arcs and Birkeland currents: Evidence for plasma sheet boundary waves

Quasi‐periodic structures of small‐scale Birkeland currents, energetic electrons, ion drifts, and auroral forms in the dawn sector have been observed simultaneously with the HILAT spacecraft. These structures map to the Low Latitude Boundary Layer using a model geomagnetic field. This mapping is supported by the observed characteristics of the energetic electrons and the relationship between precipitating electrons, Region 1 Birkeland currents, and plasma drift. These observations are interpreted as the result of quasi‐periodic variations of the Low Latitude Boundary Layer. Values of potential, estimated from assumed characteristics of a large‐scale wave propagating in this layer, agree with those determined from the HILAT particle and drift measurements. These results support the view that wave propagation at the Low Latitude Boundary Layer/Plasma Sheet interface can be a source of multiple auroral forms at low altitudes. We suggest that the Kelvin‐Helmholtz instability may be the ultimate source of these waves.