Statistics of Multi‐MeV Electron Drift‐Periodic Flux Oscillations Using Van Allen Probes Observations

Zhao, Hong; Sarris, T. E.; Li, Xinlin; Huckabee, Isabella G.; Baker, D. N.; Jaynes, Allison; Kanekal, S. G.

doi:10.1029/2022gl097995

Cited by 3 publications

(2 citation statements)

References 40 publications

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“…Both inner and outer terrestrial radiation belt fluxes typically display drift-periodic oscillations. Depending on the situation, these drift-periodic signatures can be interpreted as drift echoes following MLT-localized injections, dropout echoes following MLT-localized losses, or evidence of trapped particles' drift resonance with ULF waves (e.g., Sauvaud et al, 2013;Hao et al, 2016;Patel et al, 2019;Lejosne and Mozer, 2020;Zhao et al, 2022). Drift echoes have also been reported in Saturnian radiation belt fluxes (e.g., Hao et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Drift phase resolved diffusive radiation belt model: 1. Theoretical framework

Lejosne

Albert

2023

Front. Astron. Space Sci.

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Most physics-based models provide a coarse three-dimensional representation of radiation belt dynamics at low time resolution, of the order of a few drift periods. The description of the effect of trapped particle transport on radiation belt intensity is based on the random phase approximation, and it is in one dimension only: the third adiabatic invariant coordinate, akin to a phase-averaged radial distance. This means that these radiation belt models do not resolve the drift phase or, equivalently, the magnetic local time. Yet, in situ measurements suggest that radiation belt intensity frequently depends on magnetic local time, at least transiently, such as during active times. To include processes generating azimuthal variations in trapped particle fluxes and to quantify their relative importance in radiation belt energization, an improvement in the spatiotemporal resolution of the radiation belt models is required. The objective of this study is to pave the way for a new generation of diffusive radiation belt models capable of retaining drift phase information. Specifically, we highlight a two-dimensional equation for the effects of trapped particle transport on radiation belt intensity. With a theoretical framework that goes beyond the radial diffusion paradigm, the effects of trapped particle bulk motion, as well as diffusion, are quantified in terms of Euler potentials, α,β, quantities akin to the radial and azimuthal directions. This work provides the theoretical foundations underlying the drift phase resolved transport equation for radiation belt dynamics. It also brings forward the concept of azimuthal diffusion as a phase-mixing agent.

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Section: Introductionmentioning

confidence: 99%

Drift phase resolved diffusive radiation belt model: 1. Theoretical framework

Lejosne

Albert

2023

Front. Astron. Space Sci.

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“…On the other hand, one telltale signature of ongoing radial diffusion is the periodic flux oscillations of radiation belt electrons with frequencies near the electron drift frequency (Hartinger et al, 2020;O'Brien et al, 2022;Sarris et al, 2017Sarris et al, , 2020Sarris et al, , 2021Schulz & Lanzerotti, 1974;Zhao et al, 2021Zhao et al, , 2022. The flux oscillations provide insight into the resonant interaction between the radiation belt particles and ultra-low-frequency (ULF) waves and the radial diffusion processes, allowing a greater understanding of electron belt dynamics.…”

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confidence: 99%

Design and Instrument Characterization of the High‐Energy Resolution Relativistic Electron Telescope (HERT) Using Geant4 Simulation

Krantz,

Zhao,

Blum

et al. 2023

JGR Space Physics

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Earth's outer radiation belt is filled with relativistic (∼100s of keV–3 MeV) and ultrarelativistic (∼>3 MeV) electrons. The acceleration of electrons to these high energies are believed to be caused by inward radial transport and local acceleration, but the relative importance of the two mechanisms to electrons with different energies are still under considerate debate. In the post Van Allen Probes era, measurements of radiation belt populations must rely on small space missions such as CubeSats and SmallSats. The Miniaturized High‐Energy‐Resolution relativistic electron Telescope (HERT) is a compact (≤3U) telescope designed for a CubeSat mission in geosynchronous transfer orbit (GTO). HERT's main objective is to provide high‐energy‐resolution measurements of outer belt electrons in an energy range of ∼1–7 MeV to help differentiate the contribution of inward radial transport and local acceleration. Geant4 simulations were conducted to characterize the instrument responses. A novel method of using a spherical cap particle source in Geant4 simulation was developed for more efficient instrument characterization. Combined with Bow tie analysis, it is demonstrated that HERT will have an energy resolution of 5% for ∼1.5–3 MeV electrons and 12% for ∼3–7 MeV with current electronics design. In addition, using the AE9 model, we showed the instrument would have statistically sufficient count rates in the outer belt while not saturating the electronics. With a compact configuration and higher energy resolution in comparison to previous instruments, HERT will significantly contribute to the quantitative understanding of the radiation belt electron dynamics.

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Characteristic times for radiation belt drift phase mixing

Lejosne,

Albert,

Ratliff

2024

Front. Astron. Space Sci.

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Impulsive radial transport events occurring in the radiation belts leave lasting marks in the form of drift echoes, that is, energy-dependent drift phase structures in the radiation belts that evolve at the drift frequency. Drift echoes are known to be transient structures that dissipate due to phase mixing. The objective of this paper is to discuss how much time it takes for drift echoes to dissipate, and what drives this phase-mixing process. While any uncertainty or perturbation in the variables controlling trapped particles’ drift frequency contributes to phase mixing, we highlight two main drivers: the observational uncertainty associated with the finite size of the instrument energy channels, and the natural field fluctuations driving perturbations in trapped particles’ drift frequency. It is the combination of both instrumental and natural sources of phase mixing that determines the observed dissipation and lifetime of drift echoes. This means that the observed magnitude and lifetime of a drift echo are always underestimations of the natural magnitude and lifetime of the structure. This calls into question the applicability of the standard, drift-averaged formulation of radial diffusion. The three key points of the study are the following: First, the time it takes for particles initially localized in local time to phase-mix is measured in hours in the Earth’s radiation belts. Second, phase mixing at the drift scale is primarily due to uncertainties in measured kinetic energy and field perturbations. Third, our analysis can be utilized to set an energy resolution requirement for future particle instruments.

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Statistics of Multi‐MeV Electron Drift‐Periodic Flux Oscillations Using Van Allen Probes Observations

Cited by 3 publications

References 40 publications

Drift phase resolved diffusive radiation belt model: 1. Theoretical framework

Drift phase resolved diffusive radiation belt model: 1. Theoretical framework

Design and Instrument Characterization of the High‐Energy Resolution Relativistic Electron Telescope (HERT) Using Geant4 Simulation

Characteristic times for radiation belt drift phase mixing

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