Nonlinear processes

• We elucidated the theoretical conditions for which electrostatic three-wave decay should dominate scattering off thermal ions and showed that these constraints are consistent with existing simulations and with observations in type III sources [Cairns, 2000]. This analysis also showed that the simulations are in the wrong domain to properly model type III and foreshock waves, predicting wave levels that are far too high and domination of scattering off thermal ions, whereas the observed type III and foreshock waves are typically in the domain predicted for ES decay.
• The roles played by electrostatic waves in producing radio emissions were reviewed, treating nonlinear processes, linear mode conversion, and mechanisms involving localized wave packets [Cairns and Robinson, 2000].
• We generalized the nonlinear dispersion equation for decay and modulational instabilities to include finite bandwidth effects [Robinson et al., 2002]. The results elucidate how finite bandwidth effects reduce the growth rate of the decay and modulational instabilities, typically requiring the electrostatic decay to proceed as a random-phase process and stabilising most modulational instabilities. However, a broadband modulational instability is confirmed to exist in a specified region of energy density - wavenumber space.

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