Modeling the Electron Flux Enhancement and Butterfly Pitch Angle Distributions on L Shells <2.5

Abstract

We analyze an energetic electron flux enhancement event in the inner radiation belt observed by Van Allen Probes during an intense geomagnetic storm. The energetic electron flux at L~1.5 increased by a factor of 3 with pronounced butterfly pitch angle distributions (PADs). Using a three‐dimensional radiation belt model, we simulate the electron evolution under the impact of radial diffusion, local wave‐particle interactions including hiss, very low frequency transmitters, and magnetosonic waves, as well as Coulomb scattering. Consistency between observation and simulation suggests that inward radial diffusion plays a dominant role in accelerating electrons up to 900 keV and transporting the butterfly PADs from higher L shells to form the butterfly PADs at L~1.5. However, local wave‐particle interactions also contribute to drive butterfly PADs at L ≳ 1.9. Our study provides a feasible mechanism to explain the electron flux enhancement in the inner belt and the persistent presence of the butterfly PADs at L~1.5.

Upper Limit of Outer Radiation Belt Electron Acceleration Driven by Whistler‐Mode Chorus Waves

“…Van Allen Probes measurements are used to update the electron PSDs at the lower energy boundary, and we set the electron PSDs at the upper energy boundary to be constants. We take $$f=0$$ inside the bounce loss cone, and $${D}_{\alpha \alpha }\frac{\partial f}{\partial \alpha }+{D}_{\alpha p}\frac{\partial f}{\partial p}=0$$ at $${\alpha }_{\text{eq}}=90{}^{\circ}$$ following previous studies (Albert et al., 2016; Hua et al., 2019).…”

Electron Scattering by Very‐Low‐Frequency and Low‐Frequency Waves From Ground Transmitters in the Earth's Inner Radiation Belt and Slot Region

“…In addition, at energies above several hundred keV, the pitch angle scattering by LGW and hiss causes electron scattering loss on a shorter timescale than the electron acceleration by transmitter waves (Agapitov et al., 2014; Claudepierre et al., 2020a; Green et al., 2020; Meredith et al., 2007). The electron acceleration by transmitter waves may be also slower than the transport process of radial diffusion and injections (e.g., Hua et al., 2019; Ma, Li, et al., 2017). Therefore, the electron acceleration effect by transmitter waves may be weak under most circumstances.…”

Statistics of Magnetosonic Waves in the Slot Region Observed by Van Allen Probes

“…Recent studies suggest that MS waves can scatter radiation belt electrons by both Landau and bounce resonances (S. Fu et al, 2019; and scatter ring current protons by cyclotron resonance (Fu et al, 2016;Fu & Ge, 2021). Hua et al (2019) shed light on the possible cause of consecutively attendant butterfly PADs at 1.5 ≤ L ≤ 1.8, that is, attributed to inward propagation of butterfly PADs formed at higher radial regions due to MS waves. By performing a statistical analysis of energetic electron PAD characteristics based on Van Allen Probes (VAPs) observations, C. Yang, Su et al (2017) found that energetic electron butterfly distributions in the slot region are primarily caused by MS waves.…”

“…Hua et al. (2019) shed light on the possible cause of consecutively attendant butterfly PADs at 1.5 ≤ L ≤ 1.8, that is, attributed to inward propagation of butterfly PADs formed at higher radial regions due to MS waves. By performing a statistical analysis of energetic electron PAD characteristics based on Van Allen Probes (VAPs) observations, C. Yang, Su et al.…”