Pitch-angle diffusion and the origin of temporal and spatial structures in morningside aurorae

The origin of the morningside-aurorae temporal and spatial structures is discussed. Observational evidence is presented pertaining to the role of pitch-angle diffusion in the auroral regions in the formation of these structures, namely, the observations of energetic particles by rockets and satellites, VLF waves at high altitudes, magnetospheric cold plasma, auroral emissions in the atmosphere, and magnetic pulsations detected on the ground. On the basis of this evidence, together with observations and theories related to the outer 'permanently trapped' radiation belts, several theoretical models for the modulation of VLF wave growth in the equatorial regions are pieced together. (I.S.)