Uncertainties in Theoretical Chorus Chirping Rates: A Comparative Analysis

Whistler-mode chorus waves play a critical role in the dynamics of energetic electrons in the inner magnetosphere. Extensive theoretical research has been conducted to explain the frequency chirping of chorus waves, with two primary theoretical chirping rates proposed: one associated with magnetic field inhomogeneity and the other linked to wave amplitude. The validity of these chirping rates has been a subject of debate. In this study, we compare these two theoretical chirping rates using a data set of 3,166 lower-band rising-tone chorus wave elements from Van Allen Probes observations, evaluating their statistical performance. Our analysis shows that the chirping rate associated with magnetic field inhomogeneity exhibits better agreement with observations, demonstrating higher correlation and smaller standard deviation compared to the nonlinear chirping rate. These findings suggest that both chirping rates should be considered valid expressions for chorus waves, supporting a key prediction of a recently proposed theoretical model of chorus.