Direct evidence for EMIC wave scattering of relativistic electrons in space

Zhang, X.-J.; Li, W.; Ma, Q.; Thorne, R. M.; Angelopoulos, V.; Bortnik, J.; Chen, Lunjin; Kletzing, C.; Kurth, W. S.; Hospodarsky, G. B.; Baker, D. N.; Reeves, G. D.; Spence, H. E.; Blake, J. B.; Fennell, J. F.

doi:10.1002/2016ja022521

Cited by 78 publications

(92 citation statements)

References 55 publications

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“…Here we will investigate the 27 February 2014 dropout event in which EMIC wave scattering plays an important role. The effect of EMIC wave scattering at L = 5.77 during this event have been modeled using in situ EMIC wave and plasma data observed by Van Allen Probes based on the quasi‐linear theory (Zhang et al, ). By comparing to the observed loss of radiation belt electrons, they confirmed that EMIC wave‐induced electron scattering was the dominant loss mechanism at L = 5.77.…”

Section: Observations Of Dropout Eventsmentioning

confidence: 99%

“…In contrast, Shprits et al () combined observations and modeling of the evolution of the electron flux pitch angle distribution on 17 January 2013, showing that EMIC waves provide the dominant loss mechanism of radiation belt electrons at ultrarelativistic energies. Zhang et al () also showed direct and quantitative evidence of EMIC wave‐driven relativistic electron losses in the Earth's outer radiation belt by comparing their model results with the local observations of electron pitch angle distributions on 27 February 2014. By examining the data from multiple satellites including Van Allen Probes, THEMIS, and GOES during the 30 September 2012 dropout event, Turner et al (, ) concluded that the losses at L * > ~4 were dominated by magnetopause shadowing and outward transport and the losses at lower L * regions were dominated by wave‐particle interactions.…”

Section: Introductionmentioning

confidence: 97%

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Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

et al. 2017

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To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of radiation belt electrons, three distinct radiation belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and the μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Our findings suggest that these radiation belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* < 4, while EMIC waves can efficiently scatter electrons at L* > 4. Compared to the magnetopause standoff position, it is more reliable to use LCDS to evaluate the impact of magnetopause shadowing. The evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer radiation belt.

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Section: Observations Of Dropout Eventsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

et al. 2017

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“…Li et al ., ]. Previous studies have already provided simultaneous observational evidence that the occurrence of EMIC waves can cause relativistic electron precipitation [e.g., Miyoshi et al ., ; Carson et al ., ; Kersten et al ., ; Usanova et al ., ; Clilverd et al ., ; Zhang et al ., ; Shprits et al ., , ; Su et al ., ]. Plasmaspheric hiss can scatter electrons within a broad range of energies with a longer lifetime (~1–100 days) for >~1 MeV electrons but a shorter lifetime (<~1 day) for <~200 keV electrons [e.g., Abel and Thorne , ; Li et al ., ; Meredith et al ., , ; Summers et al ., ; Thorne et al ., ; L .…”

Section: Introductionmentioning

confidence: 98%

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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“…Electromagnetic ion cyclotron (EMIC) wave is one of common emissions in the Earth's magnetosphere, whose frequency falls within the range of Pc1–Pc2 (0.1–5 Hz) geomagnetic pulsations (Anderson et al, ; Cornwall, ; Young et al, ). EMIC wave has been considered as an important candidate for heating heavy ions in the inner magnetosphere (Chen et al, ; Gao et al, ; Thorne & Horne, ; Zhang et al, ), scattering ring current protons (Carson et al, ; Xiao et al, ), and the loss of relativistic electrons in the radiation belt (Gao et al, ; Meredith et al, ; Ni et al, ; Zhang et al, ). The thermal anisotropy (T ⊥ > T ∥ ) of hot protons provides the free energy to excite EMIC waves (Anderson et al, ; Chen et al, ; Cornwall, ; Gary et al, ; Lu et al, ; Lu & Wang, ).…”

Section: Introductionmentioning

confidence: 99%

Analyzing EMIC Waves in the Inner Magnetosphere Using Long‐Term Van Allen Probes Observations

Chen

Gao

et al. 2019

JGR Space Physics

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With 64‐month magnetic data from Van Allen Probes, we have studied not only the global distribution, wave normal angle (θ), and ellipticity (ε) of electromagnetic ion cyclotron (EMIC) waves, but also the dependence of their occurrence rates and magnetic amplitudes on the AE* index (the mean value of AE index over previous 1 hr). Our results show that H+ band waves are preferentially detected at 5 ≤ L ≤ 6.5, in the noon sector. They typically have small θ (<30°) and weakly left‐hand polarization but become more oblique and linearly polarized at larger magnetic latitudes or L‐shells. With the increase of AE* index, their occurrence rate significantly increases in the noon sector, and their source region extends to dusk sector. He+ band waves usually occur in the predawn and morning sectors at 3 ≤ L ≤ 4.5. They generally have moderate θ (30 ° − 40°) and left‐hand polarization and also become more oblique and linearly polarized at larger latitudes or L‐shells. There is a clear enhancement of occurrence rate and amplitude during active geomagnetic periods, especially in the dusk and evening sectors. O+ band waves mainly occur at 3 ≤ L ≤ 4 in the predawn sector. They have either very small θ (<20°) or very large θ (>50°), and typically linear or weakly right‐hand polarization. During active periods, they mostly occur at the midnight sector and L < 3.5. As a valuable supplement to previous statistical studies, our result provides not only a more compresentive EMIC wave model for evaluating their effects on the radiation belt, but also detailed observational constraints on generation mechanisms of EMIC waves.

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Direct evidence for EMIC wave scattering of relativistic electrons in space

Cited by 78 publications

References 55 publications

Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

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

Analyzing EMIC Waves in the Inner Magnetosphere Using Long‐Term Van Allen Probes Observations

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