On the Role of ULF Waves in the Spatial and Temporal Periodicity of Energetic Electron Precipitation

Electron fluxes in Earth's radiation belts are significantly affected by their resonant interaction with whistler‐mode waves. This wave‐particle interaction often occurs via first cyclotron resonance and, when intense and nonlinear, can accelerate subrelativistic electrons to relativistic energies while also scattering them into the atmospheric loss cone. Here, we model Electron Losses and Fields INvestgation’s (ELFIN) low‐altitude satellite measurements of precipitating electron spectra with a wave‐electron interaction model to infer the profiles of whistler‐mode intensity along magnetic latitude assuming realistic waveforms and statistical models of plasma density. We then compare these profiles with a wave power spatial distribution along field lines from an empirical model. We find that this empirical model is consistent with observations of subrelativistic (<200 keV) electron precipitation events, but deviates significantly for relativistic (>200 keV) electron precipitation events at all MLTs, especially on the nightside. This may be due to the sparse coverage of wave measurements at mid‐to‐high latitudes which causes statistically averaged wave power to be likely underestimated in current empirical wave models. As a result, this discrepancy suggests that intense waves likely do propagate to higher latitudes, although further investigation is required to quantify how well this high‐latitude population can account for the observed relativistic electron precipitation.

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“…(2018), Shi et al. (2022), and Zhang, Artemyev, et al. (2022)) or local (i.e., low‐altitude, see examples in Benck et al.…”

Section: Discussionmentioning

confidence: 99%

Investigating Whistler‐Mode Wave Intensity Along Field Lines Using Electron Precipitation Measurements

et al. 2023

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“…Zhang et al., 2019). This ULF wave coupling with EMIC and whistler‐mode waves is the main mechanism responsible for quasi‐periodic wave dynamics (L. Li et al., 2022; W. Li et al., 2011; Xia et al., 2020) that further controls quasi‐periodic electron resonant scattering and subsequent precipitation‐related loss (Artemyev et al., 2021; Bashir et al., 2022; Shi et al., 2022). Other ULF wave modes and transients with a more broadband frequency spectrum can have large amplitudes (e.g., Hartinger, Angelopoulos, et al., 2013; Zhu & Kivelson, 1991) relative to normal modes and may dominate trends in statistical analysis of band‐integrated wave power.…”

Section: Discussionmentioning

confidence: 99%

Properties of Magnetohydrodynamic Normal Modes in the Earth's Magnetosphere

Hartinger,

Elsden,

Archer

et al. 2023

JGR Space Physics

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The Earth's magnetosphere supports a variety of Magnetohydrodynamic (MHD) normal modes with Ultra Low Frequencies (ULF) including standing Alfvén waves and cavity/waveguide modes. Their amplitudes and frequencies depend in part on the properties of the magnetosphere (size of cavity, wave speed distribution). In this work, we use ∼13 years of Time History of Events and Macroscale Interactions during Substorms satellite magnetic field observations, combined with linearized MHD numerical simulations, to examine the properties of MHD normal modes in the region L > 5 and for frequencies <80 mHz. We identify persistent normal mode structure in observed dawn sector power spectra with frequency‐dependent wave power peaks like those obtained from simulation ensemble averages, where the simulations assume different radial Alfvén speed profiles and magnetopause locations. We further show with both observations and simulations how frequency‐dependent wave power peaks at L > 5 depend on both the magnetopause location and the location of peaks in the radial Alfvén speed profile. Finally, we discuss how these results might be used to better model radiation belt electron dynamics related to ULF waves.

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“…However, our observations show that the new dispersed precipitation can often occur only at high energies without concurrent intense precipitation at 50–100 keV. Since the efficiency of electron scattering by whistler‐mode waves increases with decreasing energy (Albert, 2005; Glauert & Horne, 2005; Mourenas et al., 2012; Shprits et al., 2008), whistler‐mode wave driven precipitation is always characterized by larger j prec / j trap at smaller energies; for example, at ELFIN, the electron precipitation driven by whistler‐mode waves is characterized by a j prec / j trap peak at 50–100 keV (see examples of ELFIN observations in Tsai et al., 2022; Shi et al., 2022; Zhang et al., 2022). Thus, it is unlikely that whistler‐mode wave scattering is the source of the observed precipitation throughout the entire period of the new dispersed electron precipitation pattern (i.e., it cannot be the sole reason for the precipitation across all energies, or the observed dispersion).…”

Section: Possible Mechanisms Responsible For Relativistic Electron Pr...mentioning

confidence: 99%

Dispersed Relativistic Electron Precipitation Patterns Between the Ion and Electron Isotropy Boundaries

Artemyev,

Angelopoulos,

Zhang

et al. 2023

JGR Space Physics

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Relativistic electron precipitation to the Earth's atmosphere is an important loss mechanism of inner magnetosphere electrons, contributing significantly to the dynamics of the radiation belts. Such precipitation may be driven by electron resonant scattering by middle‐latitude whistler‐mode waves at dawn to noon; by electromagnetic ion cyclotron (EMIC) waves at dusk; or by curvature scattering at the isotropy boundary (at the inner edge of the electron plasma sheet anywhere on the nightside, from dusk to dawn). Using low‐altitude ELFIN and near‐equatorial THEMIS measurements, we report on a new type of relativistic electron precipitation that shares some properties with the traditional curvature scattering mechanism (occurring on the nightside and often having a clear energy/L‐shell dispersion). However, it is less common than the typical electron isotropy boundary and it is observed most often during substorms. It is seen equatorward of (and well separated from) the electron isotropy boundary and around or poleward of the ion isotropy boundary (the inner edge of the ion plasma sheet). It may be due to one or more of the following mechanisms: EMIC waves in the presence of a specific radial profile of the cold plasma density; a regional suppression of the magnetic field enhancing curvature scattering locally; and/or electron resonant scattering by kinetic Alfvén waves.

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On the Role of ULF Waves in the Spatial and Temporal Periodicity of Energetic Electron Precipitation

Abstract: Resonant scattering of energetic electrons from Earth's radiation belts by electromagnetic whistler-mode waves is the main driver of energetic electron precipitation from the outer radiation belt to the atmosphere (e.g.,

Cited by 7 publications

References 94 publications

Investigating Whistler‐Mode Wave Intensity Along Field Lines Using Electron Precipitation Measurements

Investigating Whistler‐Mode Wave Intensity Along Field Lines Using Electron Precipitation Measurements

Properties of Magnetohydrodynamic Normal Modes in the Earth's Magnetosphere

Dispersed Relativistic Electron Precipitation Patterns Between the Ion and Electron Isotropy Boundaries

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