A representative case study from the Van Allen Probes during a geomagnetic storm recovery phase reveals enhanced electron fluxes at intermediate pitch angles over energies from ~100 keV to 5 MeV coincident with broadband low-frequency electromagnetic waves. The statistical properties of these waves are used to build a model for radial diffusion via drift-bounce resonances in kinetic Alfvén eigenmodes/kinetic field-line resonances. Estimated diffusion coefficients indicate timescales for radial transport on the order of hours in storm time events at energies from <100 keV to MeVs over equatorial pitch angles from the edge of the loss cone to nearly perpendicular to the geomagnetic field. The correlation of kinetic resonances with electron depletions and enhancements during storm main phase and recovery, and the rapid diffusion these waves drive, suggests that they may modulate the outer radiation belt.
Bibliographical noteFunding Information:
This research was supported by NASA grants NNX15AF57G and NNX16AG69G and Van Allen Probes (RBSP) funding provided under NASA prime contract NAS5-01072, including the EFW investi gation (PI: J.R. Wygant, University of Minnesota) and RBSP-ECT JHU/APL under contract 967399. Data generated from theoretical models are stored on Linux workstations at the Space Sciences Laboratory at UC Berkeley and can be accessed by contacting the first author. Van Allen Probes measurements used in this study can be obtained from the following data repositories: EFW http://www.space.umn.edu/rbspefw- data/, HOPE/MAGEIS/REPT https://www. rbsp-ect.lanl.gov/science/ DataDirectories.php, and/or by directly contacting the first author.
- Alfvén waves
- field-line resonances
- radiation belts