Extremely intense whistler mode waves near the bow shock: Geotail observations

Zhang, Y.; Matsumoto, Hiroshi; Kojima, Hirotsugu; Omura, Yoshiharu

doi:10.1029/1998ja900049

Cited by 32 publications

(23 citation statements)

References 35 publications

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“…Figure 6(b) shows that the wave power required at the high-frequency band is around I(f )f /B 2 0 ∼ 10 −4 −10 −2 for θ Bn 80 • . This may be compared with in-situ detection of high-frequency whistlers observed within quasiperpendicular bow shocks (Zhang et al 1999;Hull et al 2012;Oka et al 2017). These observations found intense and relatively narrowband whistlers at frequencies f 100 Hz that were nearly parallel propagating along the ambient magnetic field.…”

Section: Resultsmentioning

confidence: 99%

“…These observations found intense and relatively narrowband whistlers at frequencies f 100 Hz that were nearly parallel propagating along the ambient magnetic field. Characteristic wave amplitudes and frequencies were δB/B 0 ∼ 0.01−0.1 and ω/Ω ce ∼ 0.1−0.4 in normalized units (Zhang et al 1999). Assuming narrowband waves with the frequency bandwidth ∆f satisfying ∆f /f 1, one may approximate I(f ) ∼ δB 2 /∆f .…”

Section: Resultsmentioning

confidence: 99%

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Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region

Katou

Amano

2019

ApJ

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We propose a novel electron acceleration mechanism, which we call stochastic shock drift acceleration (SSDA), that extends the standard shock drift acceleration (SDA) for low-energy electrons at a quasiperpendicular shock to include the effect of stochastic pitch-angle scattering. We demonstrate that the steady-state energy spectrum of electrons accelerated within the shock transition region becomes a power-law in the limit of strong scattering. The spectral index is independent of the pitch-angle scattering coefficient. On the other hand, the maximum energy attainable through the mechanism scales linearly with the pitch-angle scattering coefficient. These results have been confirmed by Monte-Carlo simulations that include finite pitch-angle anisotropy. We find that the theory can reasonably well explain in-situ observations of quasi-perpendicular Earth's bow shock. Theoretical scaling law suggests that the maximum energy increases in proportion to the square of the shock speed, indicating that the thermal electrons may be accelerated up to mildly relativistic energies by the SSDA at quasiperpendicular supernova remnant shocks. Therefore, the mechanism provides a plausible solution to the long-standing electron injection problem.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region

Katou

Amano

2019

ApJ

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“…They are also important sites for the acceleration of plasma particles to high energies and the generation of electromagnetic and electrostatic waves, which can act to energize and thermalize the plasma. Whistler waves are well-known to be an important part of the shock macroscopic structure, and thus have garnered a considerable amount of attention in theoretical (e.g., Krasnoselskikh et al, 2002;Tidman & Krall, 1971) and observational studies within or upstream of Earth's bow shock (e.g., Bale et al, 2005;Dimmock et al, 2013;Fairfield, 1974;Hull et al, 2012;Krasnosel'skikh et al, 1991;Krasnoselskikh et al, 2013;Lembege et al, 2004;Oka et al, 2017;Rodriguez & Gurnett, 1975;Walker et al, 1999;Wilson, 2016;Zhang et al, 1999, and references therein), interplanetary shocks (e.g., Lengyel-Frey et al, 1996;Wilson et al, 2013Wilson et al, , 2017, and also at planetary bow shocks, such as at Mercury (e.g., Fairfield & Behannon, 1976), Uranus (e.g., Smith et al, 1991), and Venus (e.g., Orlowski & Russell, 1991). Despite much attention, the generation mechanisms, their role in shock internal structure, and consequences to plasma transport are not fully understood.…”

Section: Introductionmentioning

confidence: 99%

MMS Observations of Intense Whistler Waves Within Earth's Supercritical Bow Shock: Source Mechanism and Impact on Shock Structure and Plasma Transport

et al. 2020

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The properties of whistler waves near lower‐hybrid frequencies within Earth's quasi‐perpendicular bow shock are examined using data from the Magnetospheric Multiscale (MMS) mission. These waves appear as right‐hand polarized wave packets propagating upstream obliquely to the magnetic field and shock normal with phase speeds from a few hundred up to 1,600 km/s. The wavelengths are near the ion inertial length scale (λ∼ 0.3–1.3 λi). Detailed analysis finds characteristics consistent with the modified two‐stream instability mechanism driven by the reflected ion and electron drift. Correlations between wave and electron anisotropy variations reveal that the whistlers are affecting electron dynamics and thus their perpendicular and parallel temperatures. The electron signatures are explainable via the interaction of magnetized electrons in the whistler induced nonmonotonic magnetic fields. These waves have intense magnetic fields (δB/B∘∼ 0.1–1) and carry sizable currents that are a significant fraction of the thermal current (|J/Jvte|∼ 0.1–0.5). The whistler‐induced currents and the electron anisotropies are sufficiently large to respectively excite high‐frequency (HF) electrostatic (>100 Hz) and HF whistler waves (f∼ 0.1–0.5 fce). Energy dissipation J·E from whistlers at 30 Hz and below range from a few thousandths to few hundredths of μW/m3. Comparisons reveal that plasma energy is converted to wave energy in the foot, whereas wave energy gets dissipated into the plasma in the ramp, where irreversible heating occurs. These observed features are indicative of an intricate coupling between small‐scale interaction processes and larger‐scale structure transpiring within the layer. Such a characterization is only made possible now with the MMS high‐time‐resolution measurements.

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“…These waves are found to cause strong pitch angle scattering across the magnetopause, and the precipitation of the electrons can contribute significantly to the dayside aurora. In particular, the whistler wave, in a band extended above the lower hybrid frequency but below the electron cyclotron frequency, carried downstream from the bow shock could also contribute to the magnetopause boundary layer processes [Smith and Tsurutani, 1976;Scudder et al, 1986;Mellott and Greenstadt, 1988;Zhang et al, 1999;Hull et al, 2012]. At the other end of the spectrum at lower frequencies, kinetic Alfvén waves (KAW) [Johnson and Cheng, 2001;Chaston et al, 2007Chaston et al, , 2008 and the electromagnetic ion cyclotron (EMIC) waves [Anderson and Fuselier, 1993;Gary et al, 1993] could also have important contribution to the particle diffusion processes.…”

Section: 1002/2014ja020141mentioning

confidence: 99%

Magnetospheric boundary perturbations on MHD and kinetic scales

Chen

Fok

2015

JGR Space Physics

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To study the magnetopause on both MHD and kinetic scales, we have analyzed two Time History of Events and Macroscale Interactions during Substorms/Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon' s Interaction with the Sun magnetopause crossings under steady slow-solar wind and minimum magnetic shear conditions. These events approximate a ground state of the magnetospheric boundary with minimum influences from large-solar wind disturbances and magnetic reconnection. Our observations reveal evidence for the Kelvin-Helmholtz instability, the quasi-periodicity of magnetopause surface waves accompanied by highly asymmetrical plasma signatures between the inbound (from magnetosheath to low-latitude boundary layer (LLBL)) and the outbound (from LLBL to magnetosheath) magnetopause crossings. Stronger plasma and magnetic gradients were observed during the outbound crossings but more gradual and volatile variations at higher frequencies during the inbounds. The scale lengths of the magnetic and plasma gradients were comparable or less than the proton gyroradius. Enhancements of lower hybrid waves occurred at the locations of strong gradients or variations. We interpreted the collocations of the lower hybrid waves and plasma gradients and their variations in terms of (1) lower hybrid instabilities that directly convert solar wind flow energy into lower hybrid waves and other wave modes in the LLBL, or (2) Kelvin-Helmholtz instability and magnetic reconnection which produce the conditions for the lower hybrid instabilities to grow. The rate of ion diffusion across the magnetopause caused by the lower hybrid instability is marginally sufficient to populate the LLBL. The diffusion coefficient of O + is~30 times larger than that of H + . The lower hybrid waves could contribute to the energy dissipation at plasma gradients in magnetopause surface wave structures and limit Kelvin-Helmholtz instability growth further downstream.

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Extremely intense whistler mode waves near the bow shock: Geotail observations

Cited by 32 publications

References 35 publications

Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region

Theory of Stochastic Shock Drift Acceleration for Electrons in the Shock Transition Region

MMS Observations of Intense Whistler Waves Within Earth's Supercritical Bow Shock: Source Mechanism and Impact on Shock Structure and Plasma Transport

Magnetospheric boundary perturbations on MHD and kinetic scales

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