Equatorial Magnetosonic Waves: Do Nonlinear Interactions Play a Role in Their Evolution?

The occurrence of nonlinear interactions between discrete wave frequencies has been shown to play a significant role in the propagation and evolution of some plasma wave modes. In this paper we take advantage of closely spaced Cluster measurements to investigate the possibility nonlinear interactions occurring between the discrete emissions that are observed in a region of Equatorial Magnetosonic Wave generation. Based on transfer function analysis, it is shown that the role of nonlinear interactions plays a negligible role in the wave evolution as the emissions propagate from one satellite to the other. A bicoherence analysis of the individual signals also fails to find the existence of nonlinear interactions in the evolution of equatorial magnetosonic waves. Plain Language Summary In space plasmas, oscillations in the background electric and magnetic fields grow from energy sources associated with populations of plasma particles that are not in equilibrium. Once generated, these plasma waves may interact with the background plasma passing their energy back to the particles. In addition, waves at different frequencies may interact with each other, passing some of their energy to waves at a third frequency. There interactions may affect the evolution of these waves as they propagate in space. In this study, we examine a specific type of plasma wave, namely, equatorial magnetosonic waves, that exist as a set of harmonic frequencies related to the gyration of a proton in a magnetic field, looking for evidence of so called wave-wave interactions in a region. No evidence is found for such interactions. Thus, it appears that these waves will evolve by exchanging energy with plasma particles but not plasma waves.