Characteristic energy range of electron scattering due to plasmaspheric hiss

Ma, Q.; Li, W.; Thorne, R. M.; Bortnik, J.; Reeves, G. D.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Spence, Harlan E.; Baker, D. N.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Angelopoulos, V.

doi:10.1002/2016ja023311

Cited by 70 publications

(86 citation statements)

References 52 publications

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“…The roles of different plasma wave modes in driving energetic electron evolution in the outer radiation belt are confirmed using recent Van Allen Probes measurements and radiation belt simulations (e.g., Glauert et al, ; Li, Ma, Thorne, et al, ; Ma, Thorne, Nishimura, et al, ; Tu et al, ). Similar timescale for radial diffusion and pitch angle scattering of electrons may occur in the slot region during the transport of energetic electrons from the outer radiation belt (e.g., Thorne et al, ).…”

Section: Introductionsupporting

confidence: 52%

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

Thorne

et al. 2017

JGR Space Physics

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We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200–600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10 day nondisturbed period following the storm, the peak of electron fluxes gradually moved from L ~ 2.7 to L ~ 2.4, and the flux levels decreased by a factor of ~2–4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a three‐dimensional diffusion code, which reproduced the energy‐dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100–200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200–600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp “top‐hat” shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.

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Section: Introductionsupporting

confidence: 52%

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

Thorne

et al. 2017

JGR Space Physics

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“…During active conditions electrons exhibit a “V”‐shaped feature (bottom right panel in Figure ) due to electron injection into the slot region, whereas during quiet conditions an “S”‐shaped structure is formed (bottom left panel in Figure ). This “S”‐shaped structure is well reproduced by energy‐dependent pitch angle scattering caused by plasmaspheric hiss together with ULF‐driven radial diffusion (Ma, Li, et al, ; Ripoll et al, ). More recently, hiss‐driven pitch angle scattering is found to account for the frequently observed reversed electron energy spectrum with abundant high‐energy and fewer lower‐energy electrons with a flux dip at several hundred keV (Zhao et al, ).…”

Section: Local Energy and Pitch Angle Scatteringmentioning

confidence: 85%

Earth's Van Allen Radiation Belts: From Discovery to the Van Allen Probes Era

2019

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Discovery of the Earth's Van Allen radiation belts by instruments flown on Explorer 1 in 1958 was the first major discovery of the Space Age. The observation of distinct inner and outer zones of trapped megaelectron volt (MeV) particles, primarily protons at low altitude and electrons at high altitude, led to early models for source and loss mechanisms including Cosmic Ray Albedo Neutron Decay for inner zone protons, radial diffusion for outer zone electrons and loss to the atmosphere due to pitch angle scattering. This scattering lowers the mirror altitude for particles in their bounce motion parallel to the Earth's magnetic field until they suffer collisional loss. A view of the belts as quasi‐static inner and outer zones of energetic particles with different sources was modified by observations made during the Solar Cycle 22 maximum in solar activity over 1989–1991. The dynamic variability of outer zone electrons was measured by the Combined Radiation Release and Effects Satellite launched in July 1990. This variability is caused by distinct types of heliospheric structure that vary with the solar cycle. The launch of the twin Van Allen Probes in August 2012 has provided much longer and more comprehensive measurements during the declining phase of Solar Cycle 24. Roughly half of moderate geomagnetic storms, determined by intensity of the ring current carried mostly by protons at hundreds of kiloelectron volts, produce an increase in trapped relativistic electron flux in the outer zone. Mechanisms for accelerating electrons of hundreds of electron volts stored in the tail region of the magnetosphere to MeVenergies in the trapping region are described in this review: prompt and diffusive radial transport and local acceleration driven by magnetospheric waves. Such waves also produce pitch angle scattering loss, as does outward radial transport, enhanced when the magnetosphere is compressed. While quasilinear simulations have been used to successfully reproduce many essential features of the radiation belt particle dynamics, nonlinear wave‐particle interactions are found to be potentially important for causing more rapid particle acceleration or precipitation. The findings on the fundamental physics of the Van Allen radiation belts potentially provide insights into understanding energetic particle dynamics at other magnetized planets in the solar system, exoplanets throughout the universe, and in astrophysical and laboratory plasmas. Computational radiation belt models have improved dramatically, particularly in the Van Allen Probes era, and assimilative forecasting of the state of the radiation belts has become more feasible. Moreover, machine learning techniques have been developed to specify and predict the state of the Van Allen radiation belts. Given the potential Space Weather impact of radiation belt variability on technological systems, these new radiation belt models are expected to play a critical role in our technological society in the future as much as meteorological models do today.

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“…This is probably caused by the enhanced pitch angle scattering loss due to plasmaspheric hiss, which is particularly efficient in precipitating the energetic electrons over ~50–300 keV. Ma et al () simulated the electron flux decay due to plasmaspheric hiss and reproduced the “ S ‐shaped” distribution of the electron energy spectrum that is commonly observed in the Earth's radiation belts (Reeves et al, ). Our result of electron flux distribution is consistent with the simulation results (Ma et al, ) regarding electron loss by hiss following injection.…”

Section: Discussionmentioning

confidence: 99%

Systematic Evaluation of Low‐Frequency Hiss and Energetic Electron Injections

Shi

et al. 2017

JGR Space Physics

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The excitation of low‐frequency (LF) plasmaspheric hiss, over the frequency range from 20 Hz to 100 Hz, is systematically investigated by comparing the hiss wave properties with electron injections at energies from tens of keV to several hundreds of keV. Both particle and wave data from the Van Allen Probes during the period from September 2012 to June 2016 are used in the present study. Our results demonstrate that the intensity of LF hiss has a clear day‐night asymmetry, and increases with increasing geomagnetic activity, similar to the behavior of normal hiss (approximately hundred of hertz to several kilohertz). The occurrence rate of LF hiss in association with electron injections is up to 80% in the outer plasmasphere (L > 4) on the dayside, and the strong correlation extends to lower L shells for more active times. In contrast, at lower L shells (L < 3.5), LF hiss is seldom associated with electron injections. The LF hiss with Poynting flux directed away from the equator is dominant at higher magnetic latitudes and higher L shells, suggesting a local amplification of LF hiss in the outer plasmasphere. The averaged electron fluxes are larger at higher L shells, where significant LF hiss wave events are observed. Our study suggests the importance of electron injections and their drift trajectories toward the dayside plasmasphere in locally amplifying the LF hiss waves detected by the Van Allen Probes.

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Characteristic energy range of electron scattering due to plasmaspheric hiss

Cited by 70 publications

References 52 publications

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

Diffusive Transport of Several Hundred keV Electrons in the Earth's Slot Region

Earth's Van Allen Radiation Belts: From Discovery to the Van Allen Probes Era

Systematic Evaluation of Low‐Frequency Hiss and Energetic Electron Injections

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