  The nonlinear amplitude modulation of known electrostatic plasma modes is
examined in a generic manner, by applying a collisionless fluid model. Both
cold (zero-temperature) and warm fluid descriptions are discussed and the
results are compared. The moderately nonlinear oscillation regime is
investigated by applying a multiple scale technique. The calculation leads to a
Nonlinear Schrodinger-type Equation (NLSE), which describes the evolution of
the slowly varying wave amplitude in time and space. The NLSE admits localized
envelope (solitary wave) solutions of bright- (pulses) or dark- (holes, voids)
type, whose characteristics (maximum amplitude, width) depend on intrinsic
plasma parameters. Effects like amplitude perturbation obliqueness, finite
temperature and defect (dust) concetration are explicitly considered. The
relevance with similar highly localized modulated wave structures observed
during recent satellite missions is discussed.
