Thinning of the Magnetotail Current Sheet Inferred From Low‐Altitude Observations of Energetic Electrons

Artemyev, А. V.; Angelopoulos, Vassilis; Zhang, X.‐J.; Runov, A.; Petrukovich, A. A.; Nakamura, R.; Tsai, Ethan; Wilkins, C.

doi:10.1029/2022ja030705

Cited by 23 publications

(28 citation statements)

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“…The primary uncertainty in nightside projections should be attributed to substorm dynamics with the formation of the thin current sheet along with very strong magnetic field‐line stretching (see examples and discussion in Artemyev, Angelopoulos, et al. (2022)). Such dynamics may be better handled by more advanced magnetic field models (such as, e.g., Sitnov et al., 2019; Stephens et al., 2019), and thus, it may be a good idea to revisit ELFIN projections during substorm dynamics when such models become publicly available.…”

Section: Statistical Resultsmentioning

confidence: 99%

“…(2022), and Capannolo et al. (2023)) or field‐line scattering signatures (see, e.g., Artemyev, Angelopoulos, et al., 2022) not only in these 12 case studies, but also for the ∼6,000 orbits (∼8,500 science zones) used for the statistical portion of this study. In addition, we only included events where energy spectra was monotonically decreasing to reduce rare phenomena such as microbursts (see Zhang, Angelopoulos, et al., 2022, for more details regarding ELFIN observations of microbursts) that may skew results.…”

Section: Data Setsmentioning

confidence: 91%

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

et al. 2023

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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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Section: Statistical Resultsmentioning

confidence: 99%

Section: Data Setsmentioning

confidence: 91%

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

et al. 2023

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“…Previous studies have shown that the scattering efficiency of plasma sheet electrons by parallel whistler‐mode waves drops significantly at energies increasing from 10 keV to 50–100 keV (Artemyev et al., 2022; Ghaffari et al., 2021; Ni, Thorne, Meredith, et al., 2011; Ni, Thorne, Shprits, et al., 2011; Panov et al., 2013). The corresponding electron minimum resonant energy is ∼5 keV in our case.…”

Section: Potential Waves Generating Energetic Electron Pitch‐angle Di...mentioning

confidence: 99%

Contribution of Kinetic Alfvén Waves to Energetic Electron Precipitation From the Plasma Sheet During a Substorm

et al. 2023

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Energetic (≳50 keV) electron precipitation from the magnetosphere to the ionosphere during substorms can be important for magnetosphere‐ionosphere coupling. Using conjugate observations between the THEMIS, ELFIN, and DMSP spacecraft during a substorm, we have analyzed the energetic electron precipitation, the magnetospheric injection, and the associated plasma waves to examine the role of waves in pitch‐angle scattering plasma sheet electrons into the loss cone. During the substorm expansion phase, ELFIN‐A observed 50–300 keV electron precipitation from the plasma sheet that was likely driven by wave‐particle interactions. The identification of the low‐altitude extent of the plasma sheet from ELFIN is aided by DMSP global auroral images. Combining quasi‐linear theory, numerical test particle simulations, and equatorial THEMIS measurements of particles and fields, we have evaluated the relative importance of kinetic Alfvén waves (KAWs) and whistler‐mode waves in driving the observed precipitation. We find that the KAW‐driven bounce‐averaged pitch‐angle diffusion coefficients Dα0α0 ${D}_{{\alpha }_{0}{\alpha }_{0}}$ near the edge of the loss cone are ∼10−6–10−5 s−1 for these energetic electrons. The Dα0α0 ${D}_{{\alpha }_{0}{\alpha }_{0}}$ due to parallel whistler‐mode waves, observed at THEMIS ∼10‐min after the ELFIN observations, are ∼10−8–10−6 s−1. Thus, at least in this case, the observed KAWs dominate over the observed whistler‐mode waves in the scattering and precipitation of energetic plasma sheet electrons during the substorm injection.

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“…For Liouville phase‐space mapping, we assume conserved first and second adiabatic invariants, that is, both plasma wave scattering and field‐line curvature scattering effects have been neglected here (Artemyev, Angelopoulos, et al., 2022; Artemyev, Neishtadt, et al., 2022; Sergeev et al., 1983; Shen et al., 2022). We then have the following relation:

\begin{align*}\hfill \mu & =\frac{E{\mathrm{sin}}^{2}{\alpha }_{eq}}{B(0,t)}=const\hfill \\ \hfill \int \nolimits_{{l}_{1}}^{{l}_{2}}\sqrt{E-\mu B(s,t)}ds& =\sqrt{E}\int \nolimits_{{l}_{1}}^{{l}_{2}}\sqrt{1-{\mathrm{sin}}^{2}{\alpha }_{eq}\frac{B(s,t)}{B(0,t)}}ds=const\hfill \end{align*}

where E is the electron energy, α eq is the pitch angle at the equator, μ is the first adiabatic invariant, B ( s , t ) is the magnetic field intensity along the field line s with B (0, t ) representing the value at the equator, and l 1 and l 2 are the magnetic mirror latitudes in the northern and southern hemisphere, respectively.…”

Section: Observationsmentioning

confidence: 99%

Energetic Electron Flux Dropouts Measured by ELFIN in the Ionospheric Projection of the Plasma Sheet

Shen,

Artemyev,

Runov

et al. 2023

JGR Space Physics

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Low‐altitude observations of magnetospheric particles provide a unique opportunity for remote probing of the magnetospheric and plasma states during active times. We present the first statistical analysis of a specific pattern in such observations, energetic electron flux dropouts in the low‐altitude projection of the plasma sheet. Using 3.5 years of data from the ELFIN CubeSats we report the occurrence distribution of 145 energetic electron flux dropout events and identify characteristics, including their prevalence in the dusk and premidnight sectors, their association with substorms and enhanced auroral activities, and their correlation with the region‐1 (R1) field‐aligned current region. We also investigate three representative dropout events which benefit from satellite conjunctions between ELFIN, GOES, and THEMIS, to better understand the magnetospheric drivers and magnetic field conditions that lead to such dropouts as viewed by ELFIN. One class of dropouts may be associated with magnetic field mapping distortions due to local enhancements and thinning of cross‐tail current sheets and amplification of R1 field‐aligned currents. The other class may be associated with the increase in perpendicular anisotropy of magnetospheric electrons due to magnetic field dipolarizations near premidnight. These plasma sheet flux dropouts at ELFIN provide a valuable tool for refining magnetospheric models, thereby improving the accuracy of field‐line mapping during substorms.

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Thinning of the Magnetotail Current Sheet Inferred From Low‐Altitude Observations of Energetic Electrons

Cited by 23 publications

References 100 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

Contribution of Kinetic Alfvén Waves to Energetic Electron Precipitation From the Plasma Sheet During a Substorm

Energetic Electron Flux Dropouts Measured by ELFIN in the Ionospheric Projection of the Plasma Sheet

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