Revised single‐spacecraft method for determining wave vector <b>k</b> and resolving space‐time ambiguity

Bellan, Paul M.

doi:10.1002/2016ja022827

Cited by 33 publications

(76 citation statements)

References 12 publications

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“…The electric field fluctuations giving rise to strong E × B drifts (052707.2-052707.9 UT) have the maximum variance direction 94°from the wave vector k (mainly electromagnetic) and satisfy k ⊥ * ffiffiffiffiffiffiffiffiffiffi r e ×r i p = 0.77 (where r e and r i are the electron and ion thermal gyroradii, respectively), consistent with the longwavelength lower hybrid wave that typically has k ⊥ * ffiffiffiffiffiffiffiffiffiffi r e ×r i p~1 (Daughton, 2003). The wave vectors are determined based on the methods established in Norgren et al (2012) and Bellan (2016). The wave vectors are determined based on the methods established in Norgren et al (2012) and Bellan (2016).…”

Section: Resultsmentioning

confidence: 99%

Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields

Chen

Wang

Hesse

et al. 2019

Geophysical Research Letters

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Kinetic structures of electron diffusion regions (EDRs) under finite guide fields in magnetotail reconnection are reported. The EDRs with guide fields 0.14–0.5 (in unit of the reconnecting component) are detected by the Magnetospheric Multiscale spacecraft. The key new features include the following: (1) cold inflowing electrons accelerated along the guide field and demagnetized at the magnetic field minimum while remaining a coherent population with a low perpendicular temperature, (2) wave fluctuations generating strong perpendicular electron flows followed by alternating parallel flows inside the reconnecting current sheet under an intermediate guide field, and (3) gyrophase bunched electrons with high parallel speeds leaving the X‐line region. The normalized reconnection rates for the three EDRs range from 0.05 to 0.3. The measurements reveal that finite guide fields introduce new mechanisms to break the electron frozen‐in condition.

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Section: Resultsmentioning

confidence: 99%

Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields

Chen

Wang

Hesse

et al. 2019

Geophysical Research Letters

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“…Fortunately, the monochromatic nature of the observed wave enabled the application of several independent methods of wavevector determination. Here we utilized four methods to provide a robust estimate of k : (1) parallel component of the wavevector derived from the correlation between velocity and magnetic field fluctuations16, (2) k -vector estimation from current and magnetic field fluctuations measured in the spacecraft frame2324, (3) comparison of spacecraft-measured gradients with their corresponding spacecraft-averaged quantities, that is, the plane-wave approximation4, and (4) phase differencing of the magnetic field fluctuations between each spacecraft25.…”

Section: Resultsmentioning

confidence: 99%

“…In the second method, we combined fluctuations of current and magnetic field in the spacecraft frame to estimate k as a function of frequency using spectral techniques recently developed by Bellan2324. Here the k -vector was derived directly from fluctuations in Δ J and Δ B measured in the spacecraft frame (see Fig.…”

Section: Resultsmentioning

confidence: 99%

“…We adopted the k -vector derived using the Bellan2324 method k =[7.1 × 10 −3 , −2.0 × 10 −2 , −2.2 × 10 −2 ] km −1 because it simultaneously leveraged data from all four spacecraft and all components of the magnetic field. Allowing for ∼30% (3- σ level) uncertainty in each individual component, we found ρ i =1.02±0.07 with wavevector angle 104±4° from the magnetic field.…”

Section: Resultsmentioning

confidence: 99%

“…( a ) Power spectral density of MMS-averaged magnetic field magnitude from 22:26:28.18–22:26:35.83 UT, ( b ) the imaginary part of the Fourier amplitudes of fluctuations in MMS-averaged J × B and ( c ) corresponding components of k ( ω ) derived using the Bellan2324 technique. At the spectral peak of ∼0.9 Hz, k =[7.1 × 10 −3 , −2.0 × 10 −2 , −2.2 × 10 −2 ] km −1 .…”

Section: Figurementioning

confidence: 99%

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Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave

et al. 2017

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Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

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Generation of turbulence in Kelvin-Helmholtz vortices at the Earth's magnetopause: Magnetospheric Multiscale observations

Hasegawa

Nakamura²,

Gershman

et al. 2019

Preprint

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The Kelvin-Helmholtz instability (KHI) at Earth's magnetopause and associated turbulence are suggested to play a role in the transport of mass and momentum from the solar wind into Earth's magnetosphere. We investigate electromagnetic turbulence observed in Kelvin-Helmholtz vortices encountered at the dusk flank magnetopause by the Magnetospheric Multiscale (MMS) spacecraft under northward interplanetary magnetic field (IMF) conditions in order to reveal its generation process, mode properties, and role. A comparison with another MMS event at the dayside magnetopause with reconnection but no KHI signatures under a similar IMF condition indicates that while high-latitude magnetopause reconnection excites a modest level of turbulence in the dayside low-latitude boundary layer, the KHI further amplifies the turbulence, leading to magnetic energy spectra with a power law index −5/3 at magnetohydrodynamic scales even in its early nonlinear phase. The mode of the electromagnetic turbulence is analyzed with a single-spacecraft method based on Ampère's law, developed by Bellan (2016, https://doi. org/10.1002/2016JA022827), for estimating wave vectors as a function of spacecraft frame frequency. The results suggest that the turbulence does not consist of propagating normal-mode waves but is due to interlaced magnetic flux tubes advected by plasma flows in the vortices. The turbulence at sub-ion scales in the early nonlinear phase of the KHI may not be the cause of the plasma transport across the magnetopause but rather a consequence of three-dimensional vortex-induced reconnection, the process that can cause an efficient transport by producing tangled reconnected field lines. Plain Language SummaryTurbulence is ubiquitous in nature and plays an important role in material mixing and energy transport. Turbulence in space plasmas is characterized by fluctuations of flow velocity and/or electromagnetic fields over a broad frequency range and/or length scales and is believed to be the key to efficient plasma transport and heating. However, its generation mechanism is not fully understood because turbulence in space is often fully developed or already relaxed when observed. By analyzing high-resolution plasma and electromagnetic field data taken by the Magnetospheric Multiscale spacecraft, we study the generation process of electromagnetic turbulence at the outer boundary of Earth's magnetosphere, called the magnetopause, where either a flow shear-driven Kelvin-Helmholtz instability or magnetic reconnection or both could drive turbulence. It is shown that while dayside reconnection generates a modest level of turbulence at the magnetopause near noon, the flow shear instability further amplifies the turbulence at the flank magnetopause. Our analysis also suggests that the turbulence may not be the primary cause of plasma transport from solar wind into the magnetosphere but rather a consequence of the flow shear-induced reconnection that is likely the primary cause of plasma transport at the dayside flank under northward solar wi...

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Revised single‐spacecraft method for determining wave vector k and resolving space‐time ambiguity

Cited by 33 publications

References 12 publications

Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields

Electron Diffusion Regions in Magnetotail Reconnection Under Varying Guide Fields

Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave

Generation of turbulence in Kelvin-Helmholtz vortices at the Earth's magnetopause: Magnetospheric Multiscale observations

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