A Theoretical Framework of Chorus Wave Excitation

We propose a self-consistent theoretical framework of chorus wave excitation, which describes the evolution of the whistler fluctuation spectrum as well as the suprathermal electron distribution function. The renormalized hot electron response is cast in the form of a Dyson-like equation, which then leads to evolution equations for nonlinear fluctuation growth and frequency shift. This approach allows us to analytically derive for the first time exactly the same expression for the chorus chirping rate originally proposed by Vomvoridis et al. (1982). Chorus chirping is shown to correspond to maximization of wave particle power exchange, where each individual wave belonging to the whistler wave packet is characterized by small nonlinear frequency shift. We also show that different interpretations of chorus chirping proposed in published literature have a consistent reconciliation within the present theoretical framework, which further illuminates the analogy with similar phenomena in fusion plasmas and free electron laser physics.

Automated summary

We propose a self-consistent theoretical framework to describe the evolution of chorus wave excitation and derive the expression for chorus chirping rate. Our study shows that chorus chirping corresponds to the maximization of wave-particle power exchange and different interpretations of chorus chirping can be reconciled within this framework.