A Tale of Two Radiation Belts: The Energy‐Dependence of Self‐Limiting Electron Space Radiation

Olifer, L.; Mann, I. R.; Kale, A.; Mauk, B. H.; Claudepierre, S. G.; Baker, D. N.; Ozeke, L. G.

doi:10.1029/2021gl095779

Cited by 17 publications

(65 citation statements)

References 36 publications

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“…Indeed, the theoretical Kennel-Petschek limit does not appear to change from storm to storm by more than a factor of approximately 2 across all energy channels. This result is consistent with that of Olifer et al (2021) where the superposed epoch analysis of the limiting flux shows that the Kennel-Petschek limit does not vary by more than a factor of 2 between the upper and lower quartiles within the ensemble of the 70 storms studied. This limit is controlled by the nature of the magnetized plasma and therefore, accordingly to our results, The black scatter plot shows the electron flux measurements, the blue line shows a fit of the relativistic kappa distribution to the spectra.…”

Section: Energy-dependent Flux Limit During Intense Stormssupporting

confidence: 91%

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A Natural Limit to the Spectral Hardness of Worst Case Electron Radiation in the Terrestrial Van Allen Belt

et al. 2022

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The flux of relativistic electrons in the terrestrial Van Allen radiation belt can vary by orders of magnitude during a geomagnetic storm. The response is typically assumed to be controlled by an often delicate balance between acceleration and loss processes. Here we analyze all 133 magnetic storms from the NASA Van Allen Probes era. We show how the belts demonstrate a repeatable response which limits not only the worst case flux, but also controls and delivers a limit to the severity of the spectral hardness, consistent with the theory of Kennel and Petschek first developed over 50 years ago. When this theory is extended to relativistic energies, the observed electron flux is seen to reach a naturally limited worst case with a clear energy dependence. Here we show how the Kennel‐Petschek theory can explain the evolution and hardening of the electron spectrum during geomagnetic storms. It also introduces an energy‐dependent maximum flux limit. This limit is never reached during the Van Allen Probes era at energies above 2.6 MeV, meanwhile, it is reached within hours at lower energies (∼100 keV) in almost every storm. No current radiation belt models include this effect; without it, they cannot accurately predict the consequent radiation dynamics. Overall, our results demonstrate how this creates a remarkable absolute natural limit to both the spectral hardness and the severity of extreme electron space radiation.

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Section: Energy-dependent Flux Limit During Intense Stormssupporting

confidence: 91%

“…A recent superposed epoch study by Olifer et al. (2021) has shown that electrons with energies below ∼850 keV are strongly affected by the presence of the Kennel‐Petschek limit during geomagnetic storms. The results from Olifer et al.…”

Section: Introductionmentioning

confidence: 99%

A Natural Limit to the Spectral Hardness of Worst Case Electron Radiation in the Terrestrial Van Allen Belt

et al. 2022

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“…In addition, based on superposed epoch analysis of 70 geomagnetic storms, the study of Olifer et al. (2021) revealed consistency of the upper limit of electron fluxes with energies <∼850 keV between the observations and the theoretical results from KP theory. However, the upper limit of MeV electron fluxes is not well captured by KP theory in either Olifer et al.…”

Section: Introductionmentioning

confidence: 85%

“…However, the upper limit of MeV electron fluxes is not well captured by KP theory in either Olifer et al. (2021) or Zhang et al. (2021), since the electron fluxes at such high energies typically do not result in wave growth, and this high energy upper flux limit still remains not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Upper Limit of Outer Radiation Belt Electron Acceleration Driven by Whistler‐Mode Chorus Waves

Hua¹,

Bortnik²,

2022

Geophysical Research Letters

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In the past few decades, numerous efforts have been made to advance our understanding of the Earth's radiation belt electron dynamics (Li & Hudson, 2019; Ripoll et al., 2020, and references therein), where wave-particle interactions play an important role in various electron acceleration and loss processes (Baker, 2021;Thorne, 2010; Thorne et al., 2021, and references therein). The study of Zhang et al. (2021) reported, for the first time, an upper limit of radiation belt electron fluxes over a wide energy range from hundreds of keV to multi-MeV based on 7-year DEMETER and 6-year Van Allen Probes measurements. The observed upper flux limit of the 100 keV-1 MeV electrons is roughly inversely proportional to the kinetic energy in the outer belt, which is consistent with theoretical predictions by Summers and Shi (2014) based on the Kennel-Petschek (KP) theory (Kennel & Petschek, 1966). In the KP theory, the pitch-angle diffusion due to wave-particle interactions leads to particle precipitation into the ionosphere and results in trapped anisotropic electron population, which itself generates whistler-mode waves and leads to further precipitation, and the wave growth rate is limited by the wave damping, leading to self-limited electron fluxes. In addition, based on superposed epoch analysis of 70 geomagnetic storms, the study of Olifer et al. ( 2021) revealed consistency of the upper limit of electron fluxes with energies <∼850 keV between the observations and the theoretical results from KP theory. However, the upper limit of MeV electron fluxes is not well captured by KP theory in either Olifer et al. (2021) or Zhang et al. (2021), since the electron fluxes at such high energies typically do not result in wave growth, and this high energy upper flux limit still remains not fully understood.

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“…For different energy channels, the loss at L* = 5.5 is ∼30 times larger than at L* = 4.0 reaching values as large as ∼100 for the highest energies. The magnitude of this loss during low LCDS events is approximately an order of magnitude more intense than has been reported in some previous superposed epoch studies (Morley et al, 2010;Murphy et al, 2018;Olifer et al, 2021;Turner et al, 2019). Second, the fractional loss is very clearly much more significant at higher energies.…”

Section: Similarity and Repeatability Of The Radiation Belt Lossmentioning

confidence: 53%

On the Similarity and Repeatability of Fast Radiation Belt Loss: Role of the Last Closed Drift Shell

et al. 2021

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Since the discovery of the Earth's Van Allen radiation belts over 50 years ago (Van Allen & Frank, 1959), determining the physical processes responsible for their dynamics have been a major focus of space physics research (e.g., Friedel et al., 2002). The dynamics of the trapped relativistic electron population with energies from hundreds of kilo electronvolts (∼100 keV) to millions of electronvolts (∼1 MeV) during geomagnetic storms is of particular interest because of their potential impact on satellite electronics through deep-dielectric charging (Baker et al., 1994). Electrons can be lost at the beginning of the storm before the subsequent acceleration of a source population to MeV energies, which can partially or completely replace those which are lost, in some cases creating radiation orders of magnitude stronger than that which existed pre-storm (e.g., Reeves et al., 2003). In particular, interaction with high-frequency plasma waves, such as chorus (e.g., Lee et al., 2013;Shprits et al., 2007), electromagnetic ion cyclotron (EMIC) (e.g., Ukhorskiy et al., 2010;Usanova et al., 2014), or plasmaspheric hiss (e.g., Thorne et al., 1973) waves, can cause loss into the atmosphere. Meanwhile, ultra-low frequency (ULF) plasma waves (Mann et al., 2016) can cause particles to be transported outwards to the last closed drift shell (LCDS) and lost at the magnetopause into the solar wind in a process known as magnetopause shadowing (e.g., Olifer et al., 2018;Turner et al., 2012). The relative importance of these processes continues to be hotly debated (Mann et al., 2018;Shprits et al., 2018). This paper, in particular, focuses on investigating whether the LCDS dynamics can explain the fast magnetopause shadowing losses.Recent studies have shown that a compression of the outer magnetospheric boundary can cause intense electron radiation belt losses occurring on very short ( 𝐴𝐴 𝐴 1 day) timescales. For example, Olifer et al. ( 2018) showed that the LCDS location of the Van Allen belt electrons and its dynamics can explain rapid and intense dropouts of relativistic electrons in some of the most intense geomagnetic storms of the last decade. It is also interesting to investigate on a statistical basis whether a substantial compression of the magnetopause, characterized by inward motion of the LCDS, can cause a radiation belt dropout in every storm and

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A Tale of Two Radiation Belts: The Energy‐Dependence of Self‐Limiting Electron Space Radiation

Cited by 17 publications

References 36 publications

A Natural Limit to the Spectral Hardness of Worst Case Electron Radiation in the Terrestrial Van Allen Belt

A Natural Limit to the Spectral Hardness of Worst Case Electron Radiation in the Terrestrial Van Allen Belt

Upper Limit of Outer Radiation Belt Electron Acceleration Driven by Whistler‐Mode Chorus Waves

On the Similarity and Repeatability of Fast Radiation Belt Loss: Role of the Last Closed Drift Shell

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