Concurrence and Coupling of EMIC and EFH Instabilities in the Hot Electron Plasma

Kinetic instabilities play an important role in the dynamics of the magnetospheric system. Generally, electrons are deemed to be unrelated to the generation of electromagnetic ion cyclotron (EMIC) waves. In this work, a parameter study is performed on the EMIC instability affected by parallel anisotropic electrons (A_e < 1) in the inner magnetosphere. The wave dispersion relation and wave growth rate are calculated by a numerical method (named PDRK/BO). The plasma instabilities are analyzed and compared by using different combination of parameters (electron temperature, anisotropy and proportion). With the increase of hot electron proportion (N_e), waves are found to grow successively at $\omega >0.5{\Omega }_H$ and $\omega >{\Omega }_H$. The minimum electron energies for cyclotron resonance with EMIC waves indicate that the unusual hydrogen band waves at $\omega >0.5{\Omega }_H$ are relevant to the electron resonance mechanism. This is different from the normal hydrogen band waves at , which are the ion resonance mode in nature. The electron firehose (EFH) modes are excited by the parallel anisotropic electrons. Due to the wave couplings between EMIC and EFH modes, the dispersion relations of EMIC waves are changed significantly, and the frequencies at peak growth rates of EMIC waves are moved regularly with the increase of N_e. Our studies suggest that the energy transfer between electrons and ions has a potential to modify EMIC instabilities, which is worthy of consideration for wave-particle interactions in the hot electron plasma especially during storm times. Besides, the results could also be applicable for other planetary magnetospheres, such as the Saturn and Jupiter.