Excitation of oblique O⁺ band EMIC waves in the inner magnetosphere driven by hot H⁺ with ring velocity distributions

Abstract

Abstract Based on the linear theory, the detailed growth rate expression of plasma waves for hot ions with ring velocity distributions is derived, which can be directly used to study the wave growth with satellite data. Using linear growth rate calculations with simple magnetic field and background plasma density models, the roles of five parameters ( N e , η H + : η He + : η O + , E r , T perp , and T para ) playing in the excitation of O + band electromagnetic ion cyclotron (EMIC) waves driven by hot H + with ring velocity distributions are investigated. Our calculations demonstrate that ring distributions with sufficiently large ring velocity V r , small perpendicular thermal spread V ⊥ , and appropriate parallel thermal spread V // could enhance the wave growth of oblique O + band EMIC waves. Moreover, our results show that O + band EMIC waves considered here are mainly unstable with large wave normal angles in a dense and rich O + background plasma, in consistent with the statistical characteristics of O + band EMIC waves previously observed by satellites. Therefore, it is indicated that hot H + with ring velocity distributions should play an important role in the excitation of O + band EMIC waves, as a necessary and useful supplement to ring current ions with temperature‐anisotropy bi‐Maxwellian distributions.