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Both magnetosonic (MS) waves and plasmaspheric hiss can resonantly scatter outer radiation belt electrons, leading to various electron pitch angle distribution. Based on electron diffusion coefficients calculations and 2-D Fokker-Planck diffusion simulations, we perform a parametric study to quantitatively investigate the net electron scattering effect and the relative contributions of simultaneously occurring hiss and MS waves with groups of different wave amplitude combinations. It is found that the combined scattering effects are dominated by pitch angle scattering due to hiss emissions at L = 4, when their amplitude is comparable to or stronger than that of MS waves, thereby producing the butterfly, top-hat, flat-top, and pancake pitch angle distributions, while the butterfly distributions can evolve over a broader energy range when MS waves join the combined scattering effects. Our results demonstrate that the relative intensities of various plasma waves play an essential role in controlling the radiation belt electron dynamics.

Plain Language Summary The Earth's outer radiation belt electrons exhibit high dynamics in terms of both pitch angle and energy distributions. Because MS waves and hiss can frequently occur simultaneously inside the plasmasphere, it is important to understand their combined scattering effects on and relative contributions to the radiation belt electron dynamics. Although a number of case studies have been performed to analyze the consequences of combined scattering by these two concurrently occurring plasma waves, there lack parametric and comprehensive investigations to look into the combined scattering effects corresponding to groups of different intensities of the two wave modes. In this letter, by combining the calculations of wave-induced electron diffusion coefficients and 2-D Fokker-Plank diffusion simulations, we quantitatively analyze electron pitch angle and energy distributions under the impacts of 255 different wave amplitude combinations of these two wave modes, which can lead to top-hat, pancake, flat-top, and butterfly PADs. Our results indicate that the relative wave amplitudes of these two waves play an essential role in controlling the dynamic variations of radiation belt electron distribution.