Nonlinear vortex structures with diverging electric fields and their relation to the black aurora

Large, radially divergent electric fields have been observed by the FREJA satellite and have been associated with black auroral curls. We interpret these structures as two‐dimensional solitary nonlinear plasma waves. In accordance with observation, we suggest that these are slowly propagating vortex structures traveling along elongated density depletions perpendicular to the magnetic field. We demonstrate that these structures are localized in space (the order of 1 km) and can have large, outwardly directed radial electric fields (the order of 1 V/m)—characteristics consistent with FREJA observations.