A MORPHOLOGICAL-STUDY OF BLACK VORTEX STREETS

Black aurora has been defined as the lack of amoral emissions in well- defined regions within diffuse aurora [Royrvik, 1976; Davis, 1978]. A particularly intriguing class of black aurora is the occurrence of bla ck vortex streets (black curls) exhibiting clockwise vorticity [Davis, 1978; Trondsen and Cogger, 1997.] An archive of low-light level all-s ky and narrow field television camera data was searched, yielding 20 e xamples of black curls. Black curls are concluded to result from the K elvin-Helmholtz instability occurring in regions of positive space cha rge. Calculated peak electric fields ranged from 80 to 300 mV/m. White curls seen in aurora that was intermediate between diffuse and discre te were sometimes found in association with black curls and even paire d with black curls to form. newly discovered Karman vortex streets. A spectroscopic measurement indicated mixed proton and electron precipit ation. Electric field configurations are proposed for the black and wh ite curl systems and the Karman vortex streets.