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Found 6 entries in the Bibliography.

Showing entries from 1 through 6


A Short-lived Three-Belt Structure for sub-MeV Electrons in the Van Allen Belts: Time Scale and Energy Dependence

In this study we focus on the radiation belt dynamics driven by the geomagnetic storms during September 2017. Besides the long-lasting three-belt structures of ultrarelativistic electrons (>2 MeV, existing for tens of days), which has been studied intensively during the Van Allen Probe era, it is found that magnetospheric electrons of hundreds of keVs can also have three-belt structures at similar L extent during storm time. Measurements of 500–800 keV electrons from MagEIS instrument onboard Van Allen Probes show double-peaked (L = 3.5 and 4.5, respectively) flux-versus-L-shell profile in the outer belt, which lasted for 2–3 days. During the time interval of such transient three-belt structure, the energy-versus-L spectrogram shows novel distributions differing from both “S-shaped” and “V-shaped” spectrograms reported previously. Such peculiar distribution also illustrates the energy-dependent occurrence of the three-belt profile. The gradual formation of “reversed energy spectrum” at L ∼ 3.5 also indicates that hiss scattering inside the plasmapause contributed to the fast decay of sub-MeV remnant belt.

Hao, Y.; Zong, Q.-G.; Zhou, X.-Z.; Zou, H.; Rankin, R.; Sun, Y.; Chen, X.; Liu, Y.; Fu, S; Baker, D.; Spence, H.; Blake, J.; Reeves, G.; Claudepierre, S.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2020

YEAR: 2020     DOI:

storage ring; three-belt structure; hiss wave; electron lifetime; Radial Transport; Van Allen Probes


Comparison of Electron Loss Models in the Inner Magnetosphere During the 2013~St. Patrick\textquoterights Day Geomagnetic Storm

Electrons with energies in the keV range play an important role in the dynamics of the inner magnetosphere. Therefore, accurately modeling electron fluxes in this region is of great interest. However, these calculations constitute a challenging task since the lifetimes of electrons that are available have limitations. In this study, we simulate electron fluxes in the energy range of 20 eV to 100 keV to assess how well different electron loss models can account for the observed electron fluxes during the Geospace Environment Modelling Challenge Event of the 2013 St. Patrick\textquoterights Day storm. Three models (Case 1, Case 2, and Case 3) of electron lifetimes due to wave-induced pitch angle scattering are used to compute the fluxes, which are compared with measurements from the Van Allen Probes. The three models consider electron losses due to interactions with whistler mode hiss waves inside the plasmasphere and with whistler mode chorus waves outside the plasmasphere. The Case 1 (historical) model produces excessive loss at low L shells before and after the storm, suggesting that it overestimates losses due to hiss during quiet times. During the storm main phase and early recovery all three models show good agreement with the observations, indicating that losses due to chorus during disturbed times are, in general, well accounted for by the models. Furthermore, the more recent Case 2 and Case 3 models show overall better agreement with the observed fluxes.

Ferradas, C.; Jordanova, V.; Reeves, G.; Larsen, B.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2019

YEAR: 2019     DOI: 10.1029/2019JA026649

electron lifetime; electron loss; numerical modeling; pitch angle scattering; Van Allen Probes; Weimer electric field model


Observations and Fokker-Planck simulations of the L-shell, energy, and pitch-angle structure of Earth\textquoterights electron radiation belts during quiet times

The evolution of the radiation belts in L-shell (L), energy (E), and equatorial pitch-angle (α0) is analyzed during the calm 11-day interval (March 4 \textendashMarch 15) following the March 1 storm 2013. Magnetic Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker-Planck simulations combined with consistent event-driven scattering modeling from whistler mode hiss waves. Three (L, E, α0)-regions persist through 11 days of hiss wave scattering; the pitch-angle dependent inner belt core (L~<2.2 and E<700 keV), pitch-angle homogeneous outer belt low-energy core (L>~5 and E~<100 keV), and a distinct pocket of electrons (L~[4.5, 5.5] and E~[0.7, 2] MeV). The pitch-angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for α0~<60\textdegree, E>100 keV, 3.5

Ripoll, -F.; Loridan, V.; Denton, M.; Cunningham, G.; Reeves, G.; ik, O.; Fennell, J.; Turner, D.; Drozdov, A; Villa, J.; Shprits, Y; Thaller, S.; Kurth, W.; Kletzing, C.; Henderson, M.; Ukhorskiy, A;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2018

YEAR: 2018     DOI: 10.1029/2018JA026111

electron lifetime; hiss waves; pitch-angle diffusion coefficient; Radiation belts; Van Allen Probes; wave particle interactions


Contemporaneous EMIC and Whistler-Mode Waves: Observations and Consequences for MeV Electron Loss

The high variability of relativistic (MeV) electron fluxes in the Earth\textquoterights radiation belts is partly controlled by loss processes involving resonant interactions with electromagnetic ion cyclotron (EMIC) and whistler-mode waves. But as previous statistical models were generated independently for each wave mode, whether simultaneous electron scattering by the two wave types has global importance remains an open question. Using >3 years of simultaneous Van Allen Probes and THEMIS measurements, we explore the contemporaneous presence of EMIC and whistler-mode waves in the same L-shell, albeit at different local times, determining the distribution of wave and plasma parameters as a function of L, Kp, and AE. We derive electron lifetimes from observations and provide the first statistics of combined effects of EMIC and whistler-mode wave scattering on MeV electrons as a function of L and geomagnetic activity. We show that MeV electron lifetimes are often strongly reduced by such combined scattering.

Zhang, X.-J.; Mourenas, D.; Artemyev, A.; Angelopoulos, V.; Thorne, R.;

Published by: Geophysical Research Letters      Published on: 07/2017

YEAR: 2017     DOI: 10.1002/2017GL073886

electron lifetime; EMIC waves; Rediation belts; relativistic electron loss; Van Allen Probes; wave particle interaction; WHISTLER-MODE WAVES


A new ionospheric electron precipitation module coupled with RAM-SCB within the geospace general circulation model

Electron precipitation down to the atmosphere due to wave-particle scattering in the magnetosphere contributes significantly to the auroral ionospheric conductivity. In order to obtain the auroral conductivity in global MHD models that are incapable of capturing kinetic physics in the magnetosphere, MHD parameters are often used to estimate electron precipitation flux for the conductivity calculation. Such an MHD approach, however, lacks self-consistency in representing the magnetosphere-ionosphere coupling processes. In this study we improve the coupling processes in global models with a more physical method. We calculate the physics-based electron precipitation from the ring current and map it to the ionospheric altitude for solving the ionospheric electrodynamics. In particular, we use the BATS-R-US (Block Adaptive Tree Scheme-Roe type-Upstream) MHD model coupled with the kinetic ring current model RAM-SCB (Ring current-Atmosphere interaction Model with Self-Consistent Magnetic field (B)) that solves pitch angle-dependent electron distribution functions, to study the global circulation dynamics during the 25\textendash26 January 2013 storm event. Since the electron precipitation loss is mostly governed by wave-particle resonant scattering in the magnetosphere, we further investigate two loss methods of specifying electron precipitation loss associated with wave-particle interactions: (1) using pitch angle diffusion coefficients Dαα(E,α) determined from the quasi-linear theory, with wave spectral and plasma density obtained from statistical observations (named as \textquotedblleftdiffusion coefficient method\textquotedblright) and (2) using electron lifetimes τ(E) independent on pitch angles inferred from the above diffusion coefficients (named as \textquotedblleftlifetime method\textquotedblright). We found that both loss methods demonstrate similar temporal evolution of the trapped ring current electrons, indicating that the impact of using different kinds of loss rates is small on the trapped electron population. However, for the precipitated electrons, the lifetime method hardly captures any precipitation in the large L shell (i.e., 4 < L < 6.5) region, while the diffusion coefficient method produces much better agreement with NOAA/POES measurements, including the spatial distribution and temporal evolution of electron precipitation in the region from the premidnight through the dawn to the dayside. Further comparisons of the precipitation energy flux to DMSP observations indicates that the new physics-based precipitation approach using diffusion coefficients for the ring current electron loss can explain the diffuse electron precipitation in the dawn sector, such as the enhanced precipitation flux at auroral latitudes and flux drop near the subauroral latitudes, but the traditional MHD approach largely overestimates the precipitation flux at lower latitudes.

Yu, Yiqun; Jordanova, Vania; Ridley, Aaron; Albert, Jay; Horne, Richard; Jeffery, Christopher;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2016

YEAR: 2016     DOI: 10.1002/2016JA022585

Diffusion Coefficient; electron lifetime; electron precipitation; ionospheric conductivity; MI coupling; Van Allen Probes; wave-particle interactions


Evolution of relativistic outer belt electrons during an extended quiescent period

To effectively study steady loss due to hiss-driven precipitation of relativistic electrons in the outer radiation belt, it is useful to isolate this loss by studying a time of relatively quiet geomagnetic activity. We present a case of initial enhancement and slow, steady decay of 700 keV - 2 MeV electron populations in the outer radiation belt during an extended quiescent period from ~15 December 2012 - 13 January 2013. We incorporate particle measurements from a constellation of satellites, including the Colorado Student Space Weather Experiment (CSSWE) CubeSat, the Van Allen Probes twin spacecraft, and THEMIS, to understand the evolution of the electron populations across pitch angle and energy. Additional data from calculated phase space density (PSD), as well as hiss and chorus wave data from Van Allen Probes, helps complete the picture of the slow precipitation loss of relativistic electrons during a quiet time. Electron loss to the atmosphere during this event is quantified through use of the Loss Index Method, utilizing CSSWE measurements at LEO. By comparing these results against equatorial Van Allen Probes electron flux data, we conclude the net precipitation loss of the outer radiation belt content to be greater than 92\%, suggesting no significant acceleration during this period, and resulting in faster electron loss rates than have previously been reported.

Jaynes, A.; Li, X.; Schiller, Q.; Blum, L.; Tu, W.; Turner, D.; Ni, B.; Bortnik, J.; Baker, D.; Kanekal, S.; Blake, J.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014JA020125

electron lifetime; hiss waves; pitch angle scattering; precipitation loss; Radiation belts; Van Allen Probes