Electron source at the outer boundary of the radiation belts: Storm time case

Lui, A. T. Y.

doi:10.1002/jgra.50220

Cited by 4 publications

(4 citation statements)

References 47 publications

(64 reference statements)

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“…The main conclusion of this study is that we have confirmed here the previous results of Taylor et al. (2004) and Lui (2013) that Earth's magnetotail is capable of rapidly and efficiently accelerating electrons to relativistic levels and PSD(M) that exceed those in the outer radiation belt (assuming transport that conserves the first adiabatic invariant). The combination of simultaneous observations using well‐calibrated data from MMS and RBSP leaves no uncertainty that the answer to the question “Can Earth's magnetotail plasma sheet produce a source of relativistic electrons for the radiation belts?” is: yes, it can.…”

Section: Interpretation Consequences and Conclusionsupporting

confidence: 90%

“…In contrast, previous analyses by Taylor et al. (2004) and Lui (2013) indicated that, at least sometimes, there may be a sufficient source of M > 300 MeV/G electrons within the magnetotail plasma sheet. While simulations using advanced models have demonstrated how magnetotail reconnection and corresponding substorm activity can result in injections of relativistic electrons directly into the outer radiation belt (Eshetu et al., 2019; Sorathia et al., 2018), injections of >300 keV electrons are rarely observed at and inside of geosynchronous orbit ( L * < ∼6; e.g., Baker et al., 1978, 1998; Birn et al., 1998).…”

Section: Introductionmentioning

confidence: 75%

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Can Earth's Magnetotail Plasma Sheet Produce a Source of Relativistic Electrons for the Radiation Belts?

Turner

Cohen

Michael

et al. 2021

Geophysical Research Letters

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Like other known planetary magnetospheres, Earth's magnetosphere acts as an efficient particle accelerator, capable of accelerating electrons to relativistic energies and quasi-stably trapping them at exceptionally high intensities in the Van Allen radiation belts (e.g., Li & Hudson, 2019). Identifying the physical mechanisms that result in particle acceleration throughout the magnetosphere remains a critical objective of magnetospheric research. Using multipoint satellite analysis of electron phase space density (PSD) as a function of the first adiabatic invariant, Mu = M ∝ E ⊥ /B, Li et al. (1997) showed that the intensity of relativistic (energy, E, ≥∼100 keV, γ ≥ 1.2) electrons observed in the radiation belts cannot be explained by adiabatic acceleration of solar wind electrons within the higher magnitude magnetic fields (B) in Earth's magnetosphere; Li et al. (1997) demonstrated that the disparity was more than three orders of magnitude between the amount of relativistic electron PSD needed to supply the outer radiation belt and that actually present in the solar wind. That was a critical result, as it confirmed that some internal acceleration process(es) is required to produce the intense levels of relativistic electrons observed in Earth's radiation belts.

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Section: Interpretation Consequences and Conclusionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 75%

Can Earth's Magnetotail Plasma Sheet Produce a Source of Relativistic Electrons for the Radiation Belts?

Turner

Cohen

Michael

et al. 2021

Geophysical Research Letters

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“…[] used observations from THEMIS to show that the phase space density (PSD) of energetic electrons associated with current disruption/dipolarization (CDD) events during nonstorm periods outside the radiation belts is high enough to account for the population of relativistic electrons in the outer radiation belt if they could be transported without significant loss. This study was followed by another study [ Lui , ] showing similar results for the 5 April 2010 magnetic storm previously examined for different aspects of the storm by others [e.g., Connors et al ., ; McComas et al ., ; Goldstein et al ., , ; Clilverd et al ., ]. These two studies by Lui emphasized that the results do not dispute the importance of an internal source in the production of energetic electrons in the radiation belts during geomagnetic storms.…”

Section: Introductionsupporting

confidence: 72%

Comparison of energetic electron intensities outside and inside the radiation belts

2014

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The intensities of energetic electrons (~25-800 keV) outside and inside Earth's radiation belts are reported using measurements from Time History of Events and Macroscale Interactions during Substorms and Van Allen Probes during nongeomagnetic storm periods. Three intervals of current disruption/dipolarization events in August 2013 were selected for comparison. The following results are obtained. (1) Phase space densities (PSDs) for the equatorially mirroring electron population at three values of the first adiabatic invariant (20, 70, and 200 MeV/G) at the outer radiation belt boundary are found to be 1 to 3 orders of magnitude higher than values measured just inside the radiation belt. (2) There is indication that substorm activity leads to PSD increases inside L = 5.5 in less than 1 h. (3) Evidence for progressive inward transport of enhanced PSDs is found. (4) Reductions and enhancements in the PSDs over L shells from 3.5 to 6 are found to occur rapidly in~2-3 h. These results suggest that (1) continual replenishments are required to maintain high levels of PSD for electrons at these energies and (2) inward radial transport of these electrons occurs in a fast timescale of a few hours.

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“…Therefore, magnetic moments ( μ ) are conserved and of course the μ uc of injected electrons at different L shells are equal. Recently, based on multisatellite observations from THEMIS, Lui () and Lui et al (, ) demonstrated that the source strength of energetic electrons associated with dipolarization at the outer radiation belt boundary during both quiet and storm periods is adequate to account for the electron intensity in the outer radiation belt, if electrons could be transported inward without significant loss. Therefore, it is possible that injected electrons observed in the inner magnetosphere come from higher L shells.…”

Section: Discussionmentioning

confidence: 99%

The Radial Propagation Characteristics of the Injection Front: A Statistical Study Based On BD‐IES and Van Allen Probes Observations

et al. 2018

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Electron flux measurements outside geosynchronous orbit (GSO) obtained by the BeiDa Imaging Electron Spectrometer instrument on board a 55° inclined GSO satellite and inside GSO obtained by the Van Allen Probes are analyzed to investigate the temporal and spatial evolutions of the substorm injection region. In 1 year data started from October 2015, 63 injection events are identified. First, our study shows that the injection signatures can be detected in a large radial extent in one single event, for example, from L ∼ 4.1 to L ∼ 9.3. Second, injection onset times are derived from the energy dispersion of particle injection signatures of each satellite. The difference of the onset times among satellites reveals that the injection boundary, termed as “injection front” in this paper, can propagate both earthward and tailward with a speed varying from a few km/s to ∼100 km/s. Third, evolutions of the upper‐cutoff magnetic moments (μuc) of injected electrons are analyzed, upon which the injection events are classified into two categories. In one category, the μuc observed by two radially separated satellites are equal taking into account the error caused by the finite width of energy channels, whereas in the other category, μuc at lower L shells are smaller than those at higher L shells.

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Electron source at the outer boundary of the radiation belts: Storm time case

Cited by 4 publications

References 47 publications

Can Earth's Magnetotail Plasma Sheet Produce a Source of Relativistic Electrons for the Radiation Belts?

Can Earth's Magnetotail Plasma Sheet Produce a Source of Relativistic Electrons for the Radiation Belts?

Comparison of energetic electron intensities outside and inside the radiation belts

The Radial Propagation Characteristics of the Injection Front: A Statistical Study Based On BD‐IES and Van Allen Probes Observations

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