Dispersion structures in the energetic ion and electron spectra in the auroral regions: Their nature, properties and implication Original Research Article

In DOK-2 experiments onboard Interball 1,2 (Lutsenko at al., 1998) we observed ∼200 dispersion structures in energetic ion and electron spectra in the auroral zones of the Earthʹs magnetosphere at ILAT=67–74° (L=6.5–13.2). Some detailed analysis results for ∼40 of these dispersion events are given. Their main characteristics show that we have deal with particles, which were injected momentary onto closed magnetic field lines from the plasma sheet and experienced a gradient-curvature drift. In some cases we observed ions from one injection making several turns around the Earth, which allowed us to find accurate values of drift periods in the real magnetic field. Due to high energy and time resolutions of DOK-2 the dispersion structure analysis may give a drift start time To with an accuracy of tens of seconds and an estimation of the acceleration process duration which was ∼1 min. The time To was compared with the time history of UVI brightening in the auroral oval. The comparison can help to determine the moment of a large-scale particle acceleration in the chain of events accompanying substorm development. For several substorms source energetic particle spectra were reconstructed from our dispersion event data.