Magnetosonic waves cause radiation belt electron butterfly distributions

Radiation belt electrons can exhibit different types of pitch angle distributions in response to various magnetospheric processes. Butterfly distributions, characterized by flux minima at pitch angles around 90°, are broadly observed in both the outer and inner belts and the slot region. By analyzing the particle and wave data collected by the Van Allen Probes during a series of geomagnetic storm, we combine test particle calculations and Fokker-Planck simulations to reveal that scattering by equatorial magnetosonic waves cause the formation of energetic electron butterfly distributions in the inner magnetosphere. 

References: 

1. Li et al., (2016), Formation of energetic electron butterfly distributions by magnetosonic waves via Landau resonance, Geophysical Research Letters, https://doi.org/10.1002/2016GL067853

2. Li et al., (2016), Ultrarelativistic electron butterfly distributions created by parallel acceleration due to magnetosonic waves, Journal of Geophysical Research: Space Physics, https://doi.org/10.1002/2016JA022370

3. Li et al., (2014), Interactions between magnetosonic waves and radiation belt electrons: Comparisons of quasi-linear calculations with test particle simulations, Geophysical Research Letters,  https://doi.org/10.1002/2014GL060461