Contributions to Loss Across the Magnetopause During an Electron Dropout Event

Reeves, G. D.; Cunningham, G.; Kalliokoski, Milla; Kilpua, Emilia; Osmane, Adnane; Henderson, M. G.; Morley, S.; Hoilijoki, Sanni; Palmroth, Minna

doi:10.1029/2022ja030751

Cited by 8 publications

(9 citation statements)

References 90 publications

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“…This scattering can be modeled statistically in terms of a Fokker-Planck equation and it is observational signature is a diffusive flattening of the distribution function along the radial distance L * . With the first and second adiabatic invariant conserved, particles carried closer to Earth gain energy through a betatron process (Kulsrud 2005) as they sample a larger magnetic field, whereas particles diffusing to higher radial distances sample a weaker magnetic field, lose energy, and experience a greater likelihood of losses at the outer magnetopause boundary (Turner et al 2012;Hudson et al 2014;George et al 2022).…”

Section: Motivation and Backgroundmentioning

confidence: 99%

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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Observational studies of the Earth’s radiation belts indicate that Alfvénic fluctuations in the frequency range of 2–25 mHz accelerate electrons to relativistic energies. For decades, statistical models of radiation belts have quantified the impact of Alfvénic waves in terms of quasi-linear diffusion. However, quasi-linear models are inadequate to quantify Alfvénic radial transport occurring on timescales comparable to the azimuthal drift period of 0.1–10 MeV electrons. With recent advances in observational methodologies offering coverage of the Earth’s radiation belts on fast timescales, a theoretical framework that distinguishes between fast and diffusive radial transport can be tested for the first time in situ. In this report, we present a drift-kinetic description of radial transport for planetary radiation belts. We characterize fast linear processes and determine the conditions under which higher-order effects become dynamically significant. In the linear regime, wave–particle interactions are categorized in terms of resonant and nonresonant responses. We demonstrate that the phenomenon of zebra stripes is nonresonant and can originate from injection events in the inner radiation belts. We derive a radial diffusion coefficient for a field model that satisfies Faraday’s law and that contains two terms: one scaling as L 10 independent of the azimuthal number m, and a second scaling as m 2 L 6. In the higher-order regime, azimuthally symmetric waves with properties consistent with in situ measurements can energize 10–100 keV electrons in less than a drift period. This process provides new evidence that acceleration by Alfvénic waves in radiation belts cannot be fully contained within diffusive models.

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Section: Motivation and Backgroundmentioning

confidence: 99%

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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“…The latter mechanism called magnetopause shadowing (MPS), which is the focus of this study, has been proved to be responsible for the fast losses of both radiation belt electrons and ring current protons (e.g., George et al., 2022; Kang et al., 2018; Liemohn et al., 1999; Staples et al., 2022; Tu et al., 2014), but its relative role in the simultaneous dropout of these two populations has not been well quantified compared to other loss processes. For radiation belt electrons, Tu et al.…”

Section: Introductionmentioning

confidence: 99%

Modeling the Simultaneous Dropout of Energetic Electrons and Protons by Magnetopause Shadowing

Lyu,

Tu,

Huang

et al. 2024

Geophysical Research Letters

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Magnetopause shadowing (MPS) effect could drive a concurrent dropout of radiation belt electrons and ring current protons. However, its relative role in the dropout of both plasma populations has not been well quantified. In this work, we study the simultaneous dropout of MeV electrons and 100s keV protons during an intense geomagnetic storm in May 2017. A radial diffusion model with an event‐specific last closed drift shell is used to simulate the MPS loss of both populations. The model well captures the fast shadowing loss of both populations at L* > 4.6, while the loss at L* < 4.6, possibly due to the electromagnetic ion cyclotron wave scattering, is not captured. The observed butterfly pitch angle distributions of electron fluxes in the initial loss phase are well reproduced by the model. The initial proton losses at low pitch angles are underestimated, potentially also contributed by other mechanisms such as field line curvature scattering.

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“…Despite a great number of both observational and modeling studies having successfully explained the physical processes during electron flux dropouts in different events (e.g., Bortnik et al., 2006; Drozdov et al., 2019, 2022; George et al., 2022; Kang et al., 2018; Su et al., 2016; Tsurutani et al., 2016; Tu et al., 2014, 2019; Turner, Shprits, et al., 2012; Turner et al., 2014; Xiang et al., 2017; Zhang, Li, Ma, et al., 2016; Zhang, Li, Thorne, et al., 2016), only a limited number of studies systematically investigated the statistical distributions of the outer belt electron flux dropouts and their dependence on energies, various geomagnetic indices, and solar wind parameters. Several studies have demonstrated the important impact of the high solar wind dynamic pressure (P SW ) and southward interplanetary magnetic field (IMF) B z on producing significant electron flux dropouts (e.g., Gao et al., 2015; Gokani et al., 2022; Onsager et al., 2007; Yuan & Zong, 2013).…”

Section: Introductionmentioning

confidence: 99%

Dependence of Electron Flux Dropouts in the Earth's Outer Radiation Belt on Energy and Driving Parameters During Geomagnetic Storms

Hua,

Bortnik,

2023

JGR Space Physics

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Using 5‐year of measurements from Van Allen Probes, we present a survey of the statistical dependence of the Earth's outer radiation belt electron flux dropouts during geomagnetic storms on electron energy and various driving parameters including interplanetary magnetic field Bz, PSW, SYM‐H, and AE. By systematically investigating the dropouts over energies of 1 keV–10 MeV at L‐shells spanning 4.0–6.5, we find that the dropouts are naturally divided into three regions. The dropouts show much higher occurrence rates at energies below ∼100 keV and above ∼1 MeV compared to much smaller occurrence rate at intermediate energies around hundreds of keV. The flux decays more dramatically at energies above ∼1 MeV compared to the energies below ∼100 keV. The flux dropouts of electrons below ∼100 keV strongly depend on magnetic local time (MLT), which demonstrate high occurrence rates on the nightside (18–06 MLT), with the highest occurrence rate associated with northward Bz, strong PSW and SYM‐H, and weak AE conditions. The strongest flux decay of these dropouts is found on the nightside, which strongly depends on PSW and SYM‐H. However, there is no clear MLT dependence of the occurrence rate of relativistic electron flux dropouts above ∼1 MeV, but the flux decay of these dropouts is more significant on the dayside, with stronger decay associated with southward IMF Bz, strong PSW, SYM‐H, and AE conditions. Our statistical results are crucial for understanding of the fundamental physical mechanisms that control the outer belt electron dynamics and developing future potential radiation belt forecasting capability.

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Contributions to Loss Across the Magnetopause During an Electron Dropout Event

Abstract: The outer radiation belt can be dramatically altered by dropout events, which deplete electron fluxes by up to several orders of magnitudes in a few hours or even less (

Cited by 8 publications

References 90 publications

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Modeling the Simultaneous Dropout of Energetic Electrons and Protons by Magnetopause Shadowing

Dependence of Electron Flux Dropouts in the Earth's Outer Radiation Belt on Energy and Driving Parameters During Geomagnetic Storms

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