Analysis of processes leading to localized electron enhancements in the outer radiation belt

New information obtained about >500keV electron intensity enhancements, which have been observed intermittently close to the outer edge of the electron radiation belt, is used in conjuction with an earlier statistical study to investigate processes which could lead to such structures. The enhancements are typically of approximately 20sec duration and occur in a very narrow invariant latitude band, maximally 20 wide. The intensity increase relative to the 'normal' background level is up to a factor 10, and the 'spike' frequency of occurrence is strongly local time dependent, with more spikes observed in the night and dusk-noon sectors than in the noon-dawn sector. The processes investigated quantitatively are distortions of the magnetospheric topology in the equatorial region, wave-particle interactions and the effects of ionospheric currents. It is shown that the various processes which contribute to equatorial field disturbances can explain the observations. (author)