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 fluid 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-thermal particles, solitary waves with both density peaks and density depressions may coexist. This may have applications to magnetosperic observations, where solitary structures with lowered densities have been observed in regions where the electron distribution is also seen to be non-thermal.