Source positions of energetic particles responsible for the fine dispersion structures: numerical simulation results

More than 400 events with fine dispersion structures (FDS) in energetic particle spectra were observed in DOK-2 experiments onboard Interball-1 and -2 spacecraft in auroral regions. The discovery of these structures was possible due to high energy resolution of the spectrometer used. In previous studies we have suggested that these structures result from a gradient-curvature drift of ions and electrons after their impulsive injection (acceleration) in the nightside magnetosphere. The analysis of dispersion structures allowed us to find the injection time with an accuracy up to 10 s. In this work, numerical particle motion simulation backward in time is carried out in order to find source positions for two FDS events. In both cases the positions are found in the evening-midnight sector of MLT. The comparison of the simulation results with observations of particles that experience several turns around the Earth, explains some peculiarities of the FDS structures and may open new possibilities to check magnetic field models.