Impact of the Electron Plasma‐to‐Cyclotron Frequency Ratio on the Generation and Saturation of EMIC Waves in the Inner Magnetosphere

Abstract Statistical analyses reveal that electromagnetic ion cyclotron (EMIC) waves are critically regulated by the electron plasma‐to‐cyclotron frequency ratio ( ω pe /Ω e ), with H + (He + ) band waves favoring lower (higher) ω pe /Ω e regions. Despite different bands exhibiting distinct sensitivities to variations in ω pe /Ω e , few studies have quantitatively assessed the effects of ω pe /Ω e on wave generation and saturation. To investigate this dependence, observations of the Van Allen Probe A during 6 years were analyzed, demonstrating that ω pe /Ω e strongly governs wave distributions at L < ∼5, with H + ‐band waves prevailing at ω pe /Ω e = 2 ∼ 10 and He + ‐band waves at ω pe /Ω e = 7 ∼ 50. Furthermore, linear theory analyses and hybrid simulations reveal that for an identical maximum growth rate, higher ω pe /Ω e can marginally enhance saturation amplitudes of both bands, shorten the H + ‐band saturation time, but prolong that of He + band. Furthermore, the effects of ω pe /Ω e are incorporated into a growth rate‐based empirical model for wave saturation, providing new insights into wave modeling and magnetospheric dynamics.