Observations of Two-Layers Spectrum Formed by Simultaneous H⁺ and He⁺ Anomalous Resonance With EMIC Waves

In collisionless plasma environments, wave-particle interactions facilitate efficient energy exchange between particles and phase-coherent waves. Using Magnetospheric Multiscale mission observations, we report a novel two-layers bridge-like arcs structure in ion energy spectrum, formed by simultaneous nonlinear interactions between large-amplitude electromagnetic ion cyclotron (EMIC) waves and ions ((Formula presented.) and (Formula presented.)). Even after incorporating finite wave-field effects into the resonance condition, only a few instances exist where the minimum correction energy is lower than the observed value, thus confirming the presence of an anomalous heating mechanism. The lower-layer bridge-like arcs are formed by the interaction between (Formula presented.) and EMIC waves, while the upper-layer bridge-like arcs result from the nonlinear interaction between (Formula presented.) ions and EMIC waves. These observations present the first direct evidence of continuous energy exchange between ions and EMIC waves, providing a new perspective for studying the simultaneous nonlinear interactions between ions and EMIC waves.