Near‐Earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

Dai, Lei; Wang, Chi; Duan, Suqing; He, Zhaohai; Wygant, J. R.; Cattell, C. A.; Tao, X.; Su, Zhenpeng; Kletzing, C. A.; Baker, D. N.; Li, Xinlin; Malaspina, D.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Turner, D. L.; Reeves, G. D.; Funsten, H. O.; Spence, H. E.; Angelopoulos, V.; Fruehauff, D.; Chen, Lunjin; Thaller, S. A.; Breneman, A. W.; Tang, Xiangwei

doi:10.1002/2015gl064955

Cited by 67 publications

(80 citation statements)

References 59 publications

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“…Therefore, it would be reasonable to suggest that the energy gain process of the high‐energy (>50 keV) electron population inside GEO is primarily achieved by an efficient betatron acceleration in the course of the dipolarization. A similar conclusion was reached by Dai et al (), who examined a case of dipolarization‐related MeV electron injections inside GEO.…”

Section: Discussionsupporting

confidence: 80%

Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit

et al. 2020

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In this study we have statistically examined flux changes of 1–1,000‐keV electrons, and hydrogen, helium, and oxygen ions during local magnetic dipolarization inside geosynchronous orbit, with a focus on their pitch angle dependence. Using 144 dipolarization events that were selected in a previous study with Van Allen Probes observations in 2012–2016, we have performed a superposed epoch analysis of differential flux changes after the dipolarization onset for each species. On average the electron flux increases primarily around pitch angle (α) = 90° at >80 keV and almost isotropically at 10–50 keV. The electron flux at <5 keV increases at α = 0° and 180° but slightly decreases (or remains unchanged) at α = 90°. On the other hand, the ion flux at >80 keV increases around α = 90°, while at <30 keV it decreases nearly independent of pitch angle. Only the low‐energy (<5 keV) helium and oxygen ion flux changes indicate a strong field‐aligned enhancement, which could be attributed to their outflows from the topside ionosphere. After the dipolarization onset, >5‐keV electron and >30‐keV ion fluxes exhibit a perpendicular anisotropy, which is most pronounced for 50–200‐keV electrons. Both distributions become more isotropic with decreasing energy. A noticeable field‐aligned anisotropy is seen for <5‐keV ion fluxes. These statistical pitch angle‐dependent electron and ion properties during dipolarizations may be explained by combining various processes, including adiabatic acceleration and/or transport, wave‐particle interactions, and ion outflow.

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Section: Discussionsupporting

confidence: 80%

Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit

et al. 2020

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“…In the course of the dipolarizing magnetic field, a strong westward electric field (a few mV/m up to several tens of mV/m) is often observed in the inner magnetosphere (Aggson et al, ; Dai et al, ; Ohtani et al, ). Such electric fields, which are likely inductive, are possibly responsible for local nonadiabatic acceleration, which leads to the mass‐dependent injection signature (Delcourt, ).…”

Section: Introductionmentioning

confidence: 99%

Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit

et al. 2018

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This paper examines how hydrogen, helium, and oxygen (H, He, and O) ion fluxes at 1–1,000 keV typically respond to local magnetic dipolarization inside geosynchronous orbit. We extracted 144 dipolarizations that occurred at magnetic inclination >30° from the 2012–2016 tail seasons' observations of the Van Allen Probes spacecraft and then defined typical flux changes of these ion species by performing a superposed epoch analysis. On average, the dipolarization inside geosynchronous orbit is accompanied by a precursory transient decrease in the northward magnetic field component, transient impulsive enhancement in the westward electric field component, and decrease (increase) in the proton density (temperature). The coincident ion species experience an energy‐dependent flux change, consisting of enhancement (depression) at energies above (below) ~50 keV. These properties morphologically resemble those around dipolarization fronts (or fast flows) in the near‐Earth tail. A distinction among the ion species is the average energy of the flux ratio peak, being at 200–400 keV (100–200 keV) for He (H and O) ions. The flux ratio peaks at different energies likely reflect the different charge states of injected ionospheric and/or solar wind origin ion species. The ion spectra become harder for sharp dipolarizations, suggesting the importance of accompanying electric field in transporting and/or energizing the ions efficiently. Interestingly, the average flux ratio peak does not differ significantly among the ion species for ~2 min after onset, which implies that mass‐dependent acceleration process is less important in the initial stage of dipolarization.

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“…While radial diffusion caused by ULF waves can redistribute relativistic electrons and change the energy of MeV electrons, which depends on the radial gradient of the electron PSDs [e.g., Elkington et al, 1999;Hudson et al, 1999;Ukhorskiy et al, 2009;Huang et al, 2010;Su et al, 2015]. Recently, some studies have also shown that enhanced convection and substorm electron injections can directly explain the rapid enhancement of the outer radiation belt [e.g., Kress et al, 2014;Dai et al, 2014Dai et al, , 2015Su et al, 2014c;Tang et al, 2016b].…”

Section: Introductionmentioning

confidence: 99%

The effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt

Tang

Wang

et al. 2017

JGR Space Physics

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Using the electron phase space density (PSD) data measured by Van Allen Probe A from January 2013 to April 2015, we investigate the effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt during 50 geomagnetic storms. A statistical study shows that the maximum electron PSDs for various μ (μ = 630, 1096, 2290, and 3311 MeV/G) at L*~4.0 after the storm peak have good correlations with storm intensity (cc~0.70). This suggests that the occurrence and magnitude of geomagnetic storms are necessary for relativistic electron enhancements at the inner edge of the outer radiation belt (L* = 4.0). For moderate or weak storm events (SYM‐Hmin > ~−100 nT) with weak substorm activity (AEmax < 800 nT) and strong storm events (SYM‐Hmin ≤ ~−100 nT) with intense substorms (AEmax ≥ 800 nT) during the recovery phase, the maximum electron PSDs for various μ at different L* values (L* = 4.0, 4.5, and 5.0) are well correlated with storm intensity (cc > 0.77). For storm events with intense substorms after the storm peak, relativistic electron enhancements at L* = 4.5 and 5.0 are observed. This shows that intense substorms during the storm recovery phase are crucial to relativistic electron enhancements in the heart of the outer radiation belt. Our statistics study suggests that magnetospheric processes during geomagnetic storms have a significant effect on relativistic electron dynamics.

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Near‐Earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations

Cited by 67 publications

References 59 publications

Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit

Pitch Angle Dependence of Electron and Ion Flux Changes During Local Magnetic Dipolarization Inside Geosynchronous Orbit

Response of Different Ion Species to Local Magnetic Dipolarization Inside Geosynchronous Orbit

The effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt

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