Nonlinear wave decay processes have been detected in the solar wind by the plasma wave experiment aboard the AMPTE-IRM spacecraft. The main process is generation of ultra-low-frequency ion-acoustic waves from the decay of Langmuir waves near the electron plasma frequency. Frequently this is accomplished by an enhancement of emissions near twice the plasma frequency. This enhancement is most likely due to the generation of electromagnetic waves from the coalescence of two Langmuir waves. These processes occur within the electron foreshock in front of the earths bow shock. Keywords Plasma frequency Langmuir waves Ion acoustic wave.
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