Excitation characteristics of EMIC waves in loss cone distributions

Electromagnetic ion cyclotron waves are an important plasma wave in the Earth's magnetosphere, which have a significant impact on the dynamics of the Earth's radiation belt and space weather events. The loss cone distribution can describe the distribution of particles deviating from the Maxwell distribution, providing a new perspective for understanding the excitation and propagation of EMIC waves. This article is based on the theory of linear plasma dispersion, and numerically calculates the EMIC wave growth rate of polar loss cone distribution ion excitation. The effects of key parameters such as loss cone parameters, particle temperature, anisotropy, plasma density, and ion proportion on EMIC wave excitation are discussed. In the case of parallel propagation, a decrease of loss cone parameter value $ \varDelta $, an increase of loss cone parameter value $ \beta $, an increase in ion temperature, and an increase in temperature anisotropy all lead to a significant increase in the EMIC wave growth rate. This indicates that a steeper loss cone distribution and vertical temperature anisotropy are beneficial for the excitation of EMIC waves. Under oblique propagation conditions, as the plasma density increases, the angle range of wave occurrence expands from 70° ~ 89° to 10° ~ 89°, and the frequency range shifts from near ΩH to between 0.6 ~ 0.9 ΩH. Moreover, the wave growth rate also increases significantly, indicating that plasma density affects the frequency and propagation angle range of EMIC waves. Meanwhile, as the proportion of hydrogen ions increases and the proportion of helium and oxygen ions decreases, the growth rate of EMIC waves gradually increases, indicating that heavy ion components will suppress the growth of hydrogen-band waves.