TY  - JOUR
A1  - Shprits, Yuri
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
JF  - Journal of geophysical research : Space physics
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.
KW  - radiation belts
KW  - ultra-relativistic electrons
KW  - EMIC waves
KW  - modeling;
KW  - plasma density
KW  - chorus waves
Y1  - 2022
U6  - https://doi.org/10.1029/2021JA030214
SN  - 2169-9380
SN  - 2169-9402
VL  - 127
IS  - 5
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Saikin, Anthony
A1  - Jordanova, Vania K.
A1  - Zhang, J. C.
A1  - Smith, C. W.
A1  - Spence, H. E.
A1  - Larsen, B. A.
A1  - Reeves, G. D.
A1  - Torbert, R. B.
A1  - Kletzing, C. A.
A1  - Zhelayskaya, I. S.
A1  - Shprits, Yuri
T1  - Comparing simulated and observed EMIC wave amplitudes using in situ Van
JF  - Journal of Atmospheric and Solar-Terrestrial Physics
N2  - We perform a statistical study calculating electromagnetic ion cyclotron (EMIC) wave amplitudes based off in situ plasma measurements taken by the Van Allen Probes’ (1.1–5.8 Re) Helium, Oxygen, Proton, Electron (HOPE) instrument. Calculated wave amplitudes are compared to EMIC waves observed by the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes during the same period. The survey covers a 22-month period (1 November 2012 to 31 August 2014), a full Van Allen Probe magnetic local time (MLT) precession. The linear theory proxy was used to identify EMIC wave events with plasma conditions favorable for EMIC wave excitation. Two hundred and thirty-two EMIC wave events (103 H+-band and 129 He+-band) were selected for this comparison. Nearly all events selected are observed beyond L = 4. Results show that calculated wave amplitudes exclusively using the in situ HOPE measurements produce amplitudes too low compared to the observed EMIC wave amplitudes. Hot proton anisotropy (Ahp) distributions are asymmetric in MLT within the inner (L < 7) magnetosphere with peak (minimum) Ahp, ∼0.81 to 1.00 (∼0.62), observed in the dawn (dusk), 0000 < MLT ≤ 1200 (1200 < MLT ≤ 2400), sectors. Measurements of Ahp are found to decrease in the presence of EMIC wave activity. Ahp amplification factors are determined and vary with respect to EMIC wave-band and MLT. He+-band events generally require double (quadruple) the measured Ahp for the dawn (dusk) sector to reproduce the observed EMIC wave amplitudes.
KW  - EMIC waves
KW  - Van Allen Probes
KW  - Linear theory
KW  - Wave generation
Y1  - 2018
U6  - https://doi.org/10.1016/j.jastp.2018.01.024
SN  - 1364-6826
SN  - 1879-1824
VL  - 177
SP  - 190
EP  - 201
PB  - Elsevier
CY  - Oxford
ER  -