Spatial relationship of visual arcs to auroral electrojets

Observations of the 5577 A (1 A = 10−10 m) emission detected with an all-sky imager are superimposed onto maps of auroral E-region coherent backscatter at 50 MHz made by the bistatic auroral radar system (BARS) to obtain the spatial and temporal relationships of stable visual arcs to auroral electrojets and the Harang discontinuity. At large aspect angles, characteristic of BARS, many eastward electron-drift velocities appear poleward of the visual arcs, in agreement with a recent proposed explanation that is based on refraction through auroral ionization structures in the E region. For some observations, the radar echoes are essentially co-located with the visual aurora. When the Harang discontinuity is present, the discrete arc separates the counterstreaming electron flow. Under these circumstances, the electric field in the E region associated with the stable arc agrees with the theoretical electric-field simulation, in which the electric field with a maximum magnitude of 40 mV m−1, reverses direction ...