Parametric Study of Oxygen Ion Bernstein Instability: Effects of Shell‐Distributed Oxygen Ions and Cool Heavy Ions

Oxygen ion cyclotron harmonic waves, observed in the Earth's magnetosphere as discrete spectral peaks near harmonics of the oxygen ion cyclotron frequency, are widely attributed to the oxygen ion Bernstein instability (OIBI) driven by hot oxygen ions of shell‐ or ring‐like velocity distributions. In this study, we conducted a systematic parametric analysis of OIBI driven by shell distributions using linear kinetic theory to examine how key plasma ion parameters affect the instability. Our results reveal that increasing the hot O + concentration enhances the growth rate and broadens the harmonic range of unstable modes. A higher shell velocity of hot O + broadens the harmonic range of unstable modes and shifts them to smaller wave numbers. In contrast, increasing the hot O + thermal spread tends to reduce the growth rate. Moreover, cool heavy ions affect instability growth differently depending on the harmonics: Cool He + and O + preferentially dampen the fourth and first harmonics, respectively.