Relativistic Electron Enhancements Through Successive Dipolarizations During a CIR-Driven Storm

Relativistic electrons in the Earth's radiation belts are highly dynamic on a variety of timescales during the geomagnetic storm. Using Van Allen Probe spacecraft data, we investigate rapid enhancements of relativistic electrons in the outer radiation belt during a corotating interaction region (CIR) driven storm. Successive dipolarizations associated with 100keV-MeV electron injections are identified. The evolution of energetic electrons is analyzed in the space of adiabatic invariants (μ, K and L*). Within less than a few hours, the phase space density (PSD) of the relativistic electrons promptly increases corresponding to injections of MeV electrons. The PSD of MeV electrons cumulatively increases by a factor of 4–10 at L* = 4.5–5.8 which is likely due to successive groups of dipolarizations and injections. Both near-equatorial (small K) and off-equatorial (large K) energetic electrons increase significantly. The increases in the near-equatorial electrons are still dominant, suggesting the operation of betatron acceleration. The event study shows that successive dipolarizations associated with the CIR-driven storm may rapidly affect relativistic electrons of the outer radiation belt over a wide range in the phase space.