Nonlinear Interaction Between H ⁺ Band and He ⁺ Band EMIC Waves: Van Allen Probe Observations and Hybrid Simulations

Nonlinear theory has predicted that wave-wave coupling from different band electromagnetic ion cyclotron (EMIC) waves can occur in multiple-ion plasmas. However, no direct observational evidence been reported yet. Here we present multiple substructures on the frequency spectrum of EMIC with observations Van Allen Probes. Some are demonstrated to be excited by nonlinear interactions between preexisting H+ and He+ through bicoherence analysis. Additionally, hybrid simulation displays a new wave is motivated at sum frequencies after two independent pump injected, implying could drive higher wavenumbers. Therefore, this letter provides first waves.