Uncertainties in Theoretical Chorus Chirping Rates: A Comparative Analysis

Whistler-mode chorus waves, characterized by discrete, repetitive, narrowband emissions with frequency chirping, play a critical role in magnetospheric dynamics particularly in radiation belt electron interactions. These waves, predominantly observed in the dawn side of Earth's magnetosphere, exhibit significant variability in chirping rates, ranging from less than 1 kHz/s to over 10 kHz/s. Over the past few decades, extensive theoretical researches have been conducted to explain the frequency chirping of chorus waves, and two typical theoretical chirping rates have been proposed, one related to magnetic field inhomogeneity and the other linked to wave amplitude. To assess the performance of these theoretical chirping rates in practical application, we automatically identify 3166 lower band rising tone chorus wave elements from Van Allen Probes observations by using a geometric method (Radon Transform), and compare the theoretical predictions with observations. Our statistical analysis reveals that the theoretical chirping rates associated with magnetic field inhomogeneity align more closely with observations than those linked to wave amplitudes. Our findings not only validate the theoretical prediction in practical application but also highlight the importance of magnetic field gradients in shaping chorus wave dynamics.