CONCLUSIONS

SGT provides a natural, quantitatively testable theory for bursty plasma waves and radio emissions associated with unstable particle distributions that persist far from their source. The combination of SGT and specific nonlinear processes provides a detailed, quantitative theoretical explanation for the persistent electron beams, bursty Langmuir waves, and radiation of solar type III bursts in the corona and solar wind. SGT also accounts quantitatively for the bursty Langmuir waves and electron beams in Earth's foreshock. Further work is required to determine, whether the nonlinear processes in the current theory for type III bursts produce the foreshock radiation, or whether the combination of linear mode conversion and reflection in density turbulence with the standard 2f_p coalescence is a viable alternative. This second option should also be considered for type III bursts. Very recent work demonstrates that many, perhaps all, interplanetary type II bursts are generated in foreshock regions upstream of shock waves driven by CMEs, as has long been suspected. These observations show streaming electrons, bursty Langmuir waves and f_p and 2f_p radiation that are qualitatively analogous to those in Earth's foreshock. This suggests that SGT will eventually provide a detailed explanation for type II bursts. The two classes of radio emissions generated in the outer heliosphere (transient emissions and the 2 kHz component) are also interpreted in terms of f_p and 2f_p radiation generated in foreshock regions, in this case upstream of shocks driven by global merged interaction regions near the heliopause. Detailed calculations using global simulations to predict the 3-D plasma density in the outer heliosphere suggest that this model can explain the 2 kHz component as f_p emission from beyond the heliopause. However, the calculations cannot explain the observed durations of the transient emissions. The research reported here on four classes of radio emissions in our solar system suggests that SGT may indeed be widely applicable to plasma waves and radio emissions in our solar system and thereby, potentially at least, to astrophysical sources.

© Copyright Astronomical Society of Australia 1997