Correlations Between Dispersive Alfvén Wave Activity, Electron Energization, and Ion Outflow in the Inner Magnetosphere

Hull, A. J.; Chaston, C. C.; Bonnell, J. W.; Damiano, P. A.; Wygant, J. R.; Reeves, G. D.

doi:10.1029/2020gl088985

Cited by 18 publications

(30 citation statements)

References 34 publications

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“…Statistical observations suggest that magnetotail electrons (first of all, cold electron populations) are indeed anisotropic (Artemyev et al, 2020;Walsh et al, 2011), whereas ions are generally isotropic (C.-P. Wang et al, 2013), but may be nongyrotropic (see discussion in Artemyev et al, 2019). Most probable origins of electron anisotropy are field-aligned cold ionospheric outflow (Walsh et al, 2013) and field-aligned electron acceleration by kinetic Alfven waves in the magnetotail (Artemyev, Rankin, & Blanco, 2015;Damiano et al, 2015;Hull et al, 2020). Ion nongyrotropy likely results from combined contributions of cold, field-aligned anisotropic beams and hot, transversely anisotropic unmagnetized ions (see discussion in R. Wang et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

Configuration of the Earth’s Magnetotail Current Sheet

Artemyev

El‐Alaoui

et al. 2021

Geophysical Research Letters

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The spatial scale and intensity of Earth’s magnetotail current sheet determine the magnetotail configuration, which is critical to one of the most energetically powerful phenomena in the Earth’s magnetosphere, substorms. In the absence of statistical information about plasma currents, theories of the magnetotail current sheets were mostly based on the isotropic stress balance. Such models suggest that thin current sheets cannot be long and should have strong plasma pressure gradients along the magnetotail. Using Magnetospheric Multiscale and THEMIS observations and global simulations, we explore realistic configuration of the magnetotail current sheet. We find that the magnetotail current sheet is thinner than expected from theories that assume isotropic stress balance. Observed plasma pressure gradients in thin current sheets are insufficiently strong (i.e., current sheets are too long) to balance the magnetic field line tension force. Therefore, pressure anisotropy is essential in the configuration of thin current sheets where instability precedes substorm onset.

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Section: Discussionmentioning

confidence: 99%

Configuration of the Earth’s Magnetotail Current Sheet

Artemyev

El‐Alaoui

et al. 2021

Geophysical Research Letters

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“…(2) upward electron beams accelerated by an electric field parallel to the magnetic field and near downward field-aligned currents [Carlson et al, 1998;Hull et al 2020]. Such low-energy ionospheric electron beams have been observed in both the magnetotail [Walsh et al, 2013;Artemyev et al, 2015] and the outer radiation belt [Kellogg et al, 2011;Mourenas et al, 2015].…”

Section: Summary and Discussionmentioning

confidence: 99%

Beam-driven ECH waves: A parametric study

et al. 2021

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Electron cyclotron harmonic (ECH) waves play a significant role in driving the diffuse aurora, which constitutes more than 75% of the particle energy input into the ionosphere. ECH waves in magnetospheric plasmas have long been thought to be excited predominantly by the loss cone anisotropy (velocity-space gradients) that arises naturally in a planetary dipole field.Recent THEMIS observations, however, indicate that an electron beam can also excite such waves in Earth's magnetotail. The ambient and beam plasma conditions under which electron beam excitation can take place are unknown. Knowledge of such conditions would allow us to further explore the relative contribution of this excitation mechanism to ECH wave scattering of magnetospheric electrons at Earth and the outer planets. Using the hot plasma dispersion relation, we address the nature of beam-driven ECH waves and conduct a comprehensive parametric survey of this instability. We find that growth is provided by beam electron cyclotron resonances of both first and higher orders. We also find that these waves are unstable under a wide range of plasma conditions. The growth rate increases with beam density, beam velocity, and hot electron temperature; it decreases with increasing beam temperature and beam temperature anisotropy (𝑇 ⊥ 𝑇 ∥ ⁄ ), hot electron density, and cold electron density and temperature. Such conditions abound in Earth's magnetotail, where magnetospheric electrons heated by earthward convection and magnetic reconnection coexist with colder ionospheric electrons.

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“…We postulate that the latitudinal width of the source area is 1°, resulting in the poleward boundary of GMLAT = 64.6° (L = 5.44). The altitude of 4,000 km and the initial pitch angle of α = 100° are based on the idea that ionospheric O + ions are uplifted by soft electron precipitation and/or Poynting flux enhancement at substorm onset and then they are further accelerated by electromagnetic disturbances in the perpendicular direction to flow out from the upper ionosphere (e.g., Chaston et al, 2004Chaston et al, , 2005Hull et al, 2020;Shen & Knudsen, 2020;Strangeway et al, 2000Strangeway et al, , 2005. The test O + ions are set to have an initial energy E k between 10 eV and 1 keV, where E k is the kth step of the 21 logarithmically equally spaced energy steps (i.e., E 1 = 10 1 eV, E 21 = 10 3 eV, and ΔE = E k+1 /E k = 10 0.1 ).…”

Section: Simulation Setupmentioning

confidence: 99%

Flux Enhancements of Field‐Aligned Low‐Energy O⁺ Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus

et al. 2022

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Flux enhancements of field‐aligned low‐energy O+ ion (FALEO) are simultaneously observed by Arase, Van Allen Probes A and B in the nightside inner magnetosphere during 05–07 UT on September 22, 2018. FALEOs appear after a magnetic dipolarization signature with approximately 6–20 min delay. It has the energy‐dispersion signature from a few keV to ∼100 eV only in the direction parallel to the magnetic field at Arase, while it decreases its energy from a few keV down to 10 eV in both the parallel and antiparallel directions at Probes A and B. We perform a numerical simulation to trace trajectories of test O+ ions in a model magnetosphere, which are launched from above the ionosphere 3–15 min after a substorm. Flying virtual satellites that have the same orbits as the real satellites, we create virtual energy‐time spectrograms of O+ ions to compare with the observed ones. Results show a very good correspondence between them, indicating that FALEOs originate from ionospheric O+ ions that are extracted from the upper ionosphere at substorm onset and flow along the magnetic field toward the geomagnetic equator. It is also revealed that 3–9 hr after their launch, test O+ ions less than 400 eV have a spatial distribution in the inner magnetosphere which is similar to those of the warm plasma cloak and the oxygen torus. We therefore conclude that FALEO is a source of those cold ion populations.

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Correlations Between Dispersive Alfvén Wave Activity, Electron Energization, and Ion Outflow in the Inner Magnetosphere

Cited by 18 publications

References 34 publications

Configuration of the Earth’s Magnetotail Current Sheet

Configuration of the Earth’s Magnetotail Current Sheet

Beam-driven ECH waves: A parametric study

Flux Enhancements of Field‐Aligned Low‐Energy O⁺ Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus

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Correlations Between Dispersive Alfvén Wave Activity, Electron Energization, and Ion Outflow in the Inner Magnetosphere

Cited by 18 publications

References 34 publications

Configuration of the Earth’s Magnetotail Current Sheet

Configuration of the Earth’s Magnetotail Current Sheet

Beam-driven ECH waves: A parametric study

Flux Enhancements of Field‐Aligned Low‐Energy O+ Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus

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Product

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Flux Enhancements of Field‐Aligned Low‐Energy O⁺ Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus