The Electromagnetic Ion Cyclotron Instability Affected by the Temperature Anisotropic Electrons in the Inner Magnetosphere

Abstract

Abstract Electromagnetic ion cyclotron (EMIC) instabilities in the inner magnetosphere are investigated with considering the effect of temperature anisotropic electrons. The perpendicular anisotropic electrons (Ae > 1) impose an inhibiting effect on EMIC instabilities, whereas parallel anisotropic electrons (Ae < 1) may generate a promoting or inhibiting effect depending on the direction of wave group velocity. The electron firehose modes can be coupled with EMIC modes. Three unanticipated secondary waves nearby the ion cyclotron frequencies are aroused by the electrons resonating with EMIC waves. The strong wave growth at proton gyrofrequency indicates that the electrons as an important energy provider for EMIC modes have been largely overlooked in previous studies. For the first time, we report a backward EMIC wave with the group velocity in opposite direction of the phase velocity. We suggest the new‐found effects from hot anisotropic electrons may improve our understanding of EMIC instabilities in the inner magnetosphere.

Keywords

• EMIC wave
• plasma instability
• wave‐particle resonance
• temperature anisotropy
• wave mode coupling
• inner magnetosphere