Abstract
AbstractNonlinear 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 has been reported yet. Here we present multiple substructures on the frequency spectrum of EMIC waves with observations of Van Allen Probes. Some substructures are demonstrated to be excited by nonlinear interactions between preexisting H+ band and He+ band EMIC waves through the bicoherence analysis. Additionally, hybrid simulation displays that a new wave is motivated at sum frequencies after two independent pump waves of different band EMIC waves are injected, implying that the nonlinear wave‐wave interactions could drive EMIC waves with higher wavenumbers. Therefore, this letter provides the first observational evidence of wave‐wave coupling between H+ band and He+ band EMIC waves.
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