Ulysses observations of nonlinear wave-wave interactions in the source regions of type III solar radio bursts

The Ulysses Unified Radio and Plasma Wave Experiment (URAP) has observed La ngmuir, ion-acoustic and associated solar type III radio emissions in the i nterplanetary medium. Bursts of 50-300 Hz (in the spacecraft frame) electri c field signals, corresponding to long-wavelength ion-acoustic waves are of ten observed coincident in time with the most intense Langmuir wave spikes, providing evidence for the electrostatic decay instability. Langmuir waves often occur as envelope solitons, suggesting that strong turbulence proces ses, such as modulational instability and soliton formation, often coexist with weak turbulence processes, such as electrostatic decay, in a few type III burst source regions.