Characteristics of Wave-Particle Power Transfer as a Function of Electron Pitch Angle in Nonlinear Frequency Chirping

Whistler mode chorus waves, common in Earth's and planetary magnetospheres, play a crucial role in energetic electron dynamics. These waves exhibit distinctive narrowband features, intense amplitudes, and frequency chirping. While numerous studies have explored chorus wave generation, an important yet often overlooked parameter is the resonant electron pitch angle. Motivated by this gap, we conduct particle-in-cell (PIC) simulations to identify the key pitch angle governing wave-particle power transfer during interactions with chorus waves. Our findings reveal that the characteristic pitch angle, which dominates power transfer, aligns with the pitch angle that minimizes the nonlinear parameter during the central portion of a chirping element. This insight supports the use of a representative pitch angle in nonlinear theories of chorus waves to estimate wave properties.