TY  - JOUR
A1  - Shprits, Yuri Y.
A1  - Allison, Hayley J.
A1  - Wang, Dedong
A1  - Drozdov, Alexander
A1  - Szabo‐Roberts, Matyas
A1  - Zhelavskaya, Irina
A1  - Vasile, Ruggero
T1  - A New Population of Ultra‐Relativistic Electrons in the Outer Radiation Zone
Y1  - 2022-05-09
VL  - 127
IS  - 5
JF  - Journal of Geophysical Research: Space Physics
DO  - 10.1029/2021JA030214
PB  - 
N2  - Van Allen Probes measurements revealed the presence of the most unusual structures in the ultra‐relativistic radiation belts. Detailed modeling, analysis of pitch angle distributions, analysis of the difference between relativistic and ultra‐realistic electron evolution, along with theoretical studies of the scattering and wave growth, all indicate that electromagnetic ion cyclotron (EMIC) waves can produce a very efficient loss of the ultra‐relativistic electrons in the heart of the radiation belts. Moreover, a detailed analysis of the profiles of phase space densities provides direct evidence for localized loss by EMIC waves. The evolution of multi‐MeV fluxes shows dramatic and very sudden enhancements of electrons for selected storms. Analysis of phase space density profiles reveals that growing peaks at different values of the first invariant are formed at approximately the same radial distance from the Earth and show the sequential formation of the peaks from lower to higher energies, indicating that local energy diffusion is the dominant source of the acceleration from MeV to multi‐MeV energies. Further simultaneous analysis of the background density and ultra‐relativistic electron fluxes shows that the acceleration to multi‐MeV energies only occurs when plasma density is significantly depleted outside of the plasmasphere, which is consistent with the modeling of acceleration due to chorus waves.
N2  - Plain Language Summary: The most energetic electrons in the Earth Van Allen radiation belts have not been accurately measured in the past. Observations for a recent NASA's Van Allen Probes missions reviled new unique structures, such as narrow rings, and posed further scientific questions. This review shows that, unlike relativistic electrons, ultra‐relativistic electrons can be very effectively locally scattered by plasma waves produced by ions, so‐called electromagnetic ion cyclotron waves. Observations also show that acceleration from MeV to multi‐MeV occurs locally by taking energy from another type of plasma wave. These waves are called whistler‐mode waves and can accelerate particles to such high energy when total plasma density is low. The difference between the relativistic and ultra‐relativistic particles justifies the classification of these particles into a different population from the bulk population of the outer radiation belt.
N2  - Key Points: Electromagnetic ion cyclotron waves effectively scatter ultra‐relativistic electrons in the radiation belts. The local acceleration produces acceleration from MeV to multi‐MeV in the regions of low density. The difference between MeV and multi‐MeV electrons justifies the classification of these particles into a new population.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/10191
ER  -