ON THE ORIGIN OF THE FORWARD VELOCITY DISPERSION OF ION EVENTS OBSERVED NEAR THE EARTHS AND JUPITER BOW SHOCK

We examined a great number of ion events observed in the vicinity of the Earth's (CCE/AMPTE, IMP-6,7, and 8) and Jupiter's (Voyager-2, Ulysses) bow shock, which showed during their onset (decay) phase earlier (later) flux increases (decreases) at higher than at lowe energies, i.e. presented forward velocity dispersion (FVD). The comparison of the whole set of observations with several theoretical frameworks (shock acceleration, ExB drift, propagation-temporal process, magnetosheath scattering) suggests that a rigidity dependent leakage process of magnetospheric ions (due to wave scattering) in the magnetosheath is most probably the main agent for the apearance of FVD of energetic (E>30keV) ions upstream and downstream from the Earth's and Jupiter's bow shock.