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Abstract:
Being a new kind of particle population distinct from the bulk population of the Earth’s radiation belts, ultra-relativistic (> ~3 MeV) electrons co-exist with the outer zone relativistic (~MeV) electrons. NASA’s Van Allen Probes (VAP) mission provides an unprecedented opportunity to understand the dynamics of ultra-relativistic electrons. A recent study (https://doi.org/10.1126/sciadv.abc0380) has demonstrated that radiation belt electrons can be accelerated up to ultra-relativistic energies (> 7 MeV) by chorus waves only under the condition of extreme cold plasma depletion (~ 10 cm-3). To comprehensively investigate the correlation between the plasma density and acceleration of ultra-relativistic electrons, we identify the enhancement events of ultra-relativistic electrons on basis of the entire VAP mission and perform a statistical analysis of their underlying relationship with the plasma density variation, which can deepen our current understanding of the physical mechanism(s) accounting for the acceleration of ultra-relativistic electrons.
