Thermal and driven stochastic grow of Langmuir waves in the solar wind andEarths' foreshock

Statistical distributions of Langmuir wave fields in the solar wind and the edge of Earth's foreshock are analyzed and compared with predictions for s tochastic growth theory (SGT). SGT quantitatively explains the solar wind, edge,and deep foreshock data as pure thermal waves, driven thermal waves su bject to net linear growth and stochastic effects, and-as waves in a pure S GT state, respectively, plus radiation near the plasma frequency f(p). Thes e changes are interpreted in terms of spatial variations in the beam instab ility's growth rate and evolution toward a pure SGT state. SGT analyses of field distributions are shown to provide a viable alternative to thermal no ise spectroscopy for wave instruments with coarse frequency resolution, and to separate f(p) radiation from Langmuir waves.