Radial transport of radiation belt electrons in kinetic field-line resonances

August 2017, Geophysical Research Letters

C. C. Chaston, J. W. Bonnell, J. R. Wygant, G. D. Reeves, D. N. Baker, D. B. Melrose, Iver H. Cairns

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.

To summarize, these researchers have found a non-linear interaction that is extremely efficient at transporting electrons radially (inward or outward). Researchers have looked at these “drift-bounce resonances” before, but by looking at the electric field in the electron’s frame of reference, it has been found that the interaction is much stronger than anyone previously thought.

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