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.
Xue et al. (2026) studied this question.