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

Motoba, T.; Ohtani, S.; Gkioulidou, M.; Mitchell, D. G.; Ukhorskiy, A. Y.; Takahashi, Kazue; Lanzerotti, L. J.; Claudepierre, S. G.; Reeves, G. D.

doi:10.1029/2019ja027543

Cited by 9 publications

(15 citation statements)

References 64 publications

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“…To understand how energetic particle injections were correlated with the concurrent local dipolarizations inside GEO, Figure 3 presents the RBSP‐A (left panels) and ‐B (right panels) observations of spin‐averaged differential fluxes of 30–470 keV electrons, and 54–270 keV hydrogen (H), 65–400 keV helium (He), and 140–400 keV oxygen (O) ions at 1730–1900 UT on 23 December 2016. During the local dipolarizations, RBSP‐A and ‐B observed typical signatures of energetic electron and ion flux enhancements (injections) inside GEO, as seen in the statistical results of Motoba et al (2020). Whereas the large‐scale injection signatures were roughly similar between the closely aligned RBSP‐A and ‐B, the shorter‐timescale variations and/or flux levels at the early stage of the injections were different between the two probes.…”

Section: Observationssupporting

confidence: 54%

“…(injections) inside GEO, as seen in the statistical results of Motoba et al (2020). Whereas the large-scale injection signatures were roughly similar between the closely aligned RBSP-A and -B, the shorter-timescale variations and/or flux levels at the early stage of the injections were different between the two probes.…”

Section: 1029/2020ja028215mentioning

confidence: 74%

“…Further studies of injections and dipolarizations inside GEO have been followed by observations from the twin satellite Van Allen Probes mission (formerly named the Radiation Belt Storm Probes: RBSP) launched in 2012 (e.g., Dai et al, 2015;Gkioulidou et al, 2015;Malaspina et al, 2015;Turner et al, 2015). Recent statistical results from the RBSP mission showed the responses of energetic particles to local dipolarizations inside GEO by performing a superposed epoch analysis (Liu et al, 2016;Motoba et al, 2018Motoba et al, , 2020Nosé et al, 2016). Whereas these statistical results yielded the average picture of the energy-, species-, and charge-state-dependent behaviors of particle injections associated with local dipolarizations, they did not capture the dynamic evolution of injections and dipolarizations and their spatial extent.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

et al. 2020

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Four closely located satellites at and inside geosynchronous orbit (GEO) provided a great opportunity to study the dynamical evolution and spatial scale of premidnight energetic particle injections inside GEO during a moderate substorm on 23 December 2016. Just following the substorm onset, the four spacecraft, a LANL satellite at GEO, the two Van Allen Probes (also called "RBSP") at~5.8 R E , and a THEMIS satellite at~5.3 R E , observed substorm-related particle injections and local dipolarizations near the central meridian (~22 MLT) of a wedge-like current system. The large-scale evolution of the electron and ion (H, He, and O) injections was almost identical at the two RBSP spacecraft with~0.5 R E apart. However, the initial short-timescale particle injections exhibited a striking difference between RBSP-A and-B: RBSP-B observed an energy dispersionless injection which occurred concurrently with a transient, strong dipolarization front (DF) with a peak-to-peak amplitude of~25 nT over~25 s; RBSP-A measured a dispersed/weaker injection with no corresponding DF. The spatiotemporally localized DF was accompanied by an impulsive, westward electric field (~20 mV m −1). The fast, impulsive E × B drift caused the radial transport of the electron and ion injection regions from GEO to~5.8 R E. The penetrating DF fields significantly altered the rapid energy-and pitch angle-dependent flux changes of the electrons and the H and He ions inside GEO. Such flux distributions could reflect the transient DF-related particle acceleration and/or transport processes occurring inside GEO. In contrast, O ions were little affected by the DF fields.

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Section: Observationssupporting

confidence: 54%

Section: 1029/2020ja028215mentioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

et al. 2020

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“…(2018); Motoba et al. (2020). The electric field was azimuthal, while it was radial in the events reported here.…”

Section: Statistical Studiesmentioning

confidence: 99%

Dipolarization Events With Inductive, Radial Electric Fields Observed by Van Allen Probes

et al. 2023

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Dipolarization events with inductive, radial electric fields are examined, using Van Allen Probes data between 2012 and 2019. Two cases are studied, followed by statistical analyses. These events were observed between evening and premidnight magnetic local times (MLTs) under moderate geomagnetic activities. Radial electric field variations, azimuthal magnetic field variations, and energetic protons were often observed when horizontal magnetic fields started to decrease in the dip region. Magnetic field lines were stretched with their motion similar to the gradient B/curvature drift velocities of energetic protons. Signs of electric fields changed when horizontal magnetic fields started to increase in the dipolarization front (DF). Electric field and magnetic field variations were correlated and in quadrature regarding the phase relation. Among other explanations, we interpret these observations in terms of energetic proton structures drifting toward the probe locations, while being accompanied by standing waves.

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“…These are characterized by strong adiabatic heating of electrons trapped within the strong magnetic field of the dipolarizing flux bundle (Birn et al, 2013(Birn et al, , 2014Gabrielse et al, 2016;Lu et al, 2016;Zaharia et al, 2000). Such heating is predominantly anisotropic and mostly increases the transverse electron energy component, creating anisotropic electron populations (Fu et al, 2012;Motoba et al, 2020;Runov et al, 2013). Instabilities of these anisotropic populations are responsible for the generation of intense whistlers (Fu et al, 2014;Malykhin et al, 2021;Tao et al, 2011), as observed around dipolarizing flux bundles (Grigorenko et al, 2020;Khotyaintsev et al, 2011;Le Contel et al, 2009;Zhang et al, 2018Zhang et al, , 2019.…”

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confidence: 99%

On the Role of Whistler‐Mode Waves in Electron Interaction With Dipolarizing Flux Bundles

2022

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The magnetotail is the main source of energetic electrons for Earth’s inner magnetosphere. Electrons are adiabatically heated during flow bursts (rapid earthward motion of the plasma) within dipolarizing flux bundles (concurrent increases and dipolarizations of the magnetic field). The electron heating is evidenced near or within dipolarizing flux bundles as rapid increases in the energetic electron flux (10–100 keV); it is often referred to as injection. The anisotropy in the injected electron distributions, which is often perpendicular to the magnetic field, generates whistler‐mode waves, also commonly observed around such dipolarizing flux bundles. Test‐particle simulations reproduce several features of injections and electron adiabatic dynamics. However, the feedback of the waves on the electron distributions has been not incorporated into such simulations. This is because it has been unclear, thus far, whether incorporating such feedback is necessary to explain the evolution of the electron pitch‐angle and energy distributions from their origin, reconnection ejecta in the mid‐tail region, to their final destination, and the electron injection sites in the inner magnetosphere. Using an analytical model we demonstrate that wave feedback is indeed important for the evolution of electron distributions. Combining canonical guiding center theory and the mapping technique we model electron adiabatic heating and scattering by whistler‐mode waves around a dipolarizing flux bundle. Comparison with spacecraft observations allows us to validate the efficacy of the proposed methodology. Specifically, we demonstrate that electron resonant interactions with whistler‐mode waves can indeed change markedly the pitch‐angle distribution of energetic electrons at the injection site and are thus critical to incorporate in order to explain the observations. We discuss the importance of such resonant interactions for injection physics and for magnetosphere‐ionosphere coupling.

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

Cited by 9 publications

References 64 publications

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Dynamic Properties of Particle Injections Inside Geosynchronous Orbit: A Multisatellite Case Study

Dipolarization Events With Inductive, Radial Electric Fields Observed by Van Allen Probes

On the Role of Whistler‐Mode Waves in Electron Interaction With Dipolarizing Flux Bundles

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