High‐resolution television observations of black aurora

Abstract

Abstract. In view of a recent revival of interest in the black aurora and related phenomena, and a striking lack of information on the phenomenon in the literature, we present high spatial and temporal resolution optical observations of the black aurora made by the University of Calgary portable auroral imager. A variety of black auroral phenomena, such as black vortices, arcs, and eastward drifting black auroral patches and arc segments, were observed in the evening and midnight sector diffuse auroral oval during a field trip to Rabbit Lake, Saskatchewan, from February 25 to March 7, 1995. Observed spatial and temporal characteristics are reviewed, with statistical data presented in the form of histograms.

Fine-scale dynamics of black auroras obtained from simultaneous imaging and particle observations with the Reimei satellite

“…Black arcs have been reported to typically drift equatorward at a few hundred meters per second [Trondsen and Cogger, 1997;Blixt and Kosch, 2004]. Black patches (black arc segments) are also observed around the midnight sector [Trondsen and Cogger, 1997;Kimball and Hallinan, 1998a]. These authors reported that the spatial scale of black patches ranges from a few hundred meters to 14 km and that they drift eastward only at 0.2-3.4 km/s.…”

“…Black arcs frequently appear in the diffuse aurora around the midnight sector, showing multiple narrow channels, each a few hundred meters to 10 km wide [Trondsen and Cogger, 1997;Blixt and Kosch, 2004]. Black arcs have been reported to typically drift equatorward at a few hundred meters per second [Trondsen and Cogger, 1997;Blixt and Kosch, 2004]. Black patches (black arc segments) are also observed around the midnight sector [Trondsen and Cogger, 1997;Kimball and Hallinan, 1998a].…”

“…Each black curl has a clockwise rotational sense [Trondsen and Cogger, 1997;Kimball and Hallinan, 1998b] (while that of auroral curls is anticlockwise), which is caused by KelvinHelmholtz instabilities in a divergent electric field [Marklund et al, 1994]. Black arcs frequently appear in the diffuse aurora around the midnight sector, showing multiple narrow channels, each a few hundred meters to 10 km wide [Trondsen and Cogger, 1997;Blixt and Kosch, 2004]. Black arcs have been reported to typically drift equatorward at a few hundred meters per second [Trondsen and Cogger, 1997;Blixt and Kosch, 2004].…”

“…Various black aurora observations have been reported [Trondsen and Cogger, 1997;Hallinan, 1998a, 1998b;Peticolas et al, 2002;Blixt and Kosch, 2004], and several kinds of black auroras have been classified, including black vortex streets (black curls), black arcs, and black patches (black rings). Black vortex streets show successive 0.5-5.7 km long black curls with a spatial separation of 1-4 km [Trondsen and Cogger, 1997;Kimball and Hallinan, 1998b]. In addition, black vortex streets drift eastward or westward at a speed of 0.2-5.0 km/s [Kimball and Hallinan, 1998b].…”

“…In addition, black vortex streets drift eastward or westward at a speed of 0.2-5.0 km/s [Kimball and Hallinan, 1998b]. Each black curl has a clockwise rotational sense [Trondsen and Cogger, 1997;Kimball and Hallinan, 1998b] (while that of auroral curls is anticlockwise), which is caused by KelvinHelmholtz instabilities in a divergent electric field [Marklund et al, 1994]. Black arcs frequently appear in the diffuse aurora around the midnight sector, showing multiple narrow channels, each a few hundred meters to 10 km wide [Trondsen and Cogger, 1997;Blixt and Kosch, 2004].…”