Whistler-mode waves play an important role in pitch-angle scattering of electrons in the Earth's magnetosphere. THEMIS mission revealed that oblique whistler-mode waves were present at dipolarization sites near the magnetic equator in the tailside around L=10. The observed wave frequencies are in the range between the proton gyrofrequency and half the electron gyrofrequency. For these obliquely propagating electromagnetic waves, not only cyclotron resonance but also Landau resonance (or transit time damping) contributes to the electron scattering [1, 2]. When the wave amplitude is small and the spectrum is broadband, the standard
quasi-linear theory is known to work quite well to describe the pitch-angle diffusion of particles (e.g., [3]). For exactly parallel propagation cases, the validity of the quasi-linear description was examined by test particle simulations (e.g., [4, 5]). However, quasi-linear
diffusion with obliquely propagating whistler mode waves has not been discussed in detail using test particle simulations. In this presentation, we study the electron pitch-angle scattering caused by the oblique whistler waves, performing test particle simulations. We specify the oblique whistler waves obeying the cold plasma dispersion relation and assume a Gaussian wave spectrum. We integrate the motion of relativistic electrons in the given electromagnetic fields and evaluate the pitch angle diffusion coefficients for different set of parameters.
We compare the numerical diffusion coefficient with those predicted by the quasi-linear theory, and discuss the dependence on the wave propagation angle relative to the background magnetic field. The results will be applied to understanding of the electron scattering process in the dipolarization sites of the Earth's magnetosphere.
