Dependence of Nonlinear Effects on Whistler‐Mode Wave Bandwidth and Amplitude: A Perspective From Diffusion Coefficients

• Published in: Journal of geophysical research. Space physics 2022-05, Vol.127 (5), p.n/a
• Main Authors: Gan, L., Li, W., Ma, Q., Artemyev, A. V., Albert, J. M.
• Format: Article
• Language: English
• Subjects: Advection; Amplitudes; Bandwidths; Broadband; Coefficients; Diffusion; Diffusion coefficient; Earth magnetosphere; Electron diffusion; Electrons; Mathematical models; Narrowband; nonlinear interactions; Pitch (inclination); quasilinear theory; Resonant interactions; Simulation; Waves; wave–particle interactions; Whistlers; whistler‐mode waves
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA030063

The electron resonant interaction with whistler‐mode waves is characterized by transport in pitch angle–energy space. We calculate electron diffusion and advection coefficients (a simplified characterization of transport) for a large range of electron pitch angle and energy using test particle simulations. Nonlinear effects are analyzed by comparing the diffusion coefficients using test particle simulations and quasilinear theory, and by evaluating the advection rates. Dependence of nonlinear effects on the wave amplitude and bandwidth of whistler‐mode waves is evaluated by running test particle simulations with a broad range of wave amplitude and bandwidth. The maximum amplitudes where the quasilinear approach is valid are found to increase with increasing bandwidth, from 50 pT for narrowband waves to 300 pT for broadband waves at L‐shell of 6. Moreover, interactions between intense whistler‐mode waves and small pitch angle electrons lead to large positive advection, which limits the applicability of diffusion‐based models. This study demonstrates the parameter range of the applicability of quasilinear theory and diffusion model for different wave amplitudes and frequency bandwidths of whistler‐mode waves, which is critical for evaluating the effects of whistler‐mode waves on energetic electrons in the Earth’s magnetosphere. Key Points The maximum wave amplitude threshold for the applicability of quasilinear theory increases with increasing bandwidth Electron diffusion acceleration due to intense broadband whistler‐mode waves is limited by phase trapping trajectory along the field line Interactions between intense whistler‐mode waves and small pitch angle electrons limit the applicability of diffusion models