Stochastic growth of localized plasma waves

Localized bursty plasma waves are detected by spacecraft in many space plas mas. The large spatiotemporal scales involved imply that beam and other ins tabilities relax to marginal stability and that mean wave energies are low. Stochastic wave growth occurs when ambient fluctuations perturb the system , causing fluctuations about marginal stability. This yields regions where growth is enhanced and others where damping is increased; bursts are associ ated with enhanced growth and can occur even when the mean growth rate is n egative. In stochastic growth, energy loss from the source is suppressed re lative to secular growth, preserving it far longer than otherwise possible. Linear stochastic growth can operate at wave levels below thresholds of no nlinear wave-clumping mechanisms such as strong-turbulence modulational ins tability and is not subject to their coherence and wavelength limits. These mechanisms can be distinguished by statistics of the fields, whose strengt hs are lognormally distributed if stochastically growing and power-law dist ributed in strong turbulence. Recent applications of stochastic growth theo ry (SGT) are described, involving bursty plasma waves and unstable particle distributions in type III solar radio sources, the Earth's foreshock, magn etosheath, and polar cap regions. It is shown that when combined with wave- wave processes, SGT also accounts for associated radio emissions. (C) 2001 American Institute of Physics.