First Observations of O2+ Band EMIC Waves in the Terrestrial Magnetosphere

Abstract

AbstractAlthough electromagnetic ion cyclotron (EMIC) waves are often known to exhibit three (H+, He+, and O+) usual bands, other peculiar minor ions (excluding He+ and O+) might also play an important role in the spectra of EMIC waves. This letter reports an interesting case that He+ band EMIC waves appear to split into O2+ and He+ band emissions. Wave frequency spectra suggesting that the organization of the wave emissions by the O2+ gyrofrequency motivates an investigation of the effects of O2+ presence on EMIC wave growth using linear theory. The calculated growth rates show that the original He+ band EMIC waves might be locally excited when O2+ is absent, while significant growth occurs for O2+ band and He+ band EMIC waves when O2+ is present. Our results provide insight into the generation of O2+ band EMIC waves.