OBSERVATIONS OF BLACK AURORAL PATCHES AND OF THEIR RELATIONSHIP TO OTHER TYPES OF AURORA

A morphological study of black patches and newly reported black rings (black patches with islands of embedded diffuse aurora) was conducted using an archive of low-light level all-sky and narrow-field televisio n camera data. The overwhelming majority of black patches and rings dr ifted eastward, poleward of westward drifting pulsating aurora in the early recovery phase of the auroral substorm. Occasionally, black auro ra would overlap with pulsating aurora. Sometimes the pulsations would add to the intensity in the black aurora more than in the surrounding diffuse aurora (called veiling). One example was documented where the pulsation was purely additive, adding to the intensity of the black a urora and the surrounding diffuse aurora equally. Cases of total veili ng suggest an intensity limit, possibly associated with the strong pit ch angle diffusion limit.