Ion-acoustic waves in a two-electron-temperature plasma: Oblique modulation and envelope excitations

Theoretical and numerical studies are carried out for the nonlinear amplitude modulation of ion-acoustic waves propagating in an unmagnetized, collisionless, three-component plasma composed of inertial positive ions moving in a background of two thermalized electron populations. Perturbations oblique to the carrier wave propagation direction have been considered. The stability analysis, based on a nonlinear Schrödinger-type equation, shows that the wave may become unstable; the stability criteria depend on the angle θ between the modulation and propagation directions. Different types of localized excitations (envelope solitary waves) are shown to exist, in qualitative agreement with satellite observations in the magnetosphere.