ION SOUND SOLITARY WAVES WITH DENSITY DEPRESSIONS

We show that a non-thermal electron distribution may change the nature of ion acoustic solitons. If the ions are assumed to respond as a flu id to perturbations in the potential, with no significant trapping in a potential well, then a thermal plasma only supports a solitary waves with a density peak. However, with a suitable distribution of non-the rmal particles, solitary waves with both density peaks and density dep ressions may coexist. This may have applications to magnetosperic obse rvations, where solitary structures with lowered densities have been o bserved in regions where the electron distribution is also seen to be non-thermal.