Large‐amplitude waves near the electron plasma frequency are found by the Magnetospheric Multiscale (MMS) mission near Earth's magnetopause. The waves are identified as Langmuir and upper hybrid (UH) ...waves, with wave vectors either close to parallel or close to perpendicular to the background magnetic field. The waves are found all along the magnetopause equatorial plane, including both flanks and close to the subsolar point. The waves reach very large amplitudes, up to 1 V m−1, and are thus among the most intense electric fields observed at Earth's magnetopause. In the magnetosphere and on the magnetospheric side of the magnetopause the waves are predominantly UH waves although Langmuir waves are also found. When the plasma is very weakly magnetized only Langmuir waves are likely to be found. Both Langmuir and UH waves are shown to have electromagnetic components, which are consistent with predictions from kinetic wave theory. These results show that the magnetopause and magnetosphere are often unstable to intense wave activity near the electron plasma frequency. These waves provide a possible source of radio emission at the magnetopause.
Key Points
Large‐amplitude upper hybrid and Langmuir waves frequently occur at Earth's magnetopause, reaching a maximum amplitude of 1 V m−1
The waves are quasi‐electrostatic but electromagnetic properties are observed
The upper hybrid and Langmuir wave properties are consistent with predictions from linear kinetic theory
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Spatial and high-time-resolution properties of the velocities, magnetic field, and 3-D electric field within plasma turbulence are examined observationally using data from the Magnetospheric ...Multiscale mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a first look at the properties of turbulence in the KHI. For the first time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra exhibit power law behavior with changes in slope near the ion gyrofrequency and lower hybrid frequency. The work provides the first observational evidence for turbulent intermittency and anisotropy consistent with quasi two-dimensional turbulence in association with the KHI. The behavior of kinetic-scale intermittency is found to have differences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics in the KHI.
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A statistical survey of plasma densities and electron distributions (0.5–100 keV) is performed using data obtained from the Time History of Events and Macroscale Interactions During Substorms ...spacecraft in near‐equatorial orbits from 1 July 2007 to 1 May 2009 in order to investigate optimum conditions for whistler mode chorus excitation. The plasma density calculated from the spacecraft potential, together with in situ magnetic field, is used to construct global maps of cyclotron and Landau resonant energies under quiet, moderate, and active geomagnetic conditions. Statistical results show that chorus intensity increases at higher AE index, with the strongest waves confined to regions where the ratio between the plasma frequency and gyrofrequency, fpe/fce, is less than 5. On the nightside, large electron anisotropies and intense chorus emissions indicate remarkable consistency with the confinement to 8 RE. Furthermore, as injected plasma sheet electrons drift from midnight through dawn toward the noon sector, their anisotropy increases and peaks on the dayside at 7 < L < 9, which is well correlated with intense chorus emissions observed in the prenoon sector. These statistical results are generally consistent with the generation of both lower‐band and upper‐band chorus through cyclotron resonant interactions with suprathermal electrons (1–100 keV). Two typical events on the nightside and dayside are studied in greater detail and additional interesting features are identified. Pancake distributions of electrons with energy below ∼2 keV, which could be responsible for the excitation of upper‐band chorus, are observed at lower L shells (<7) on the nightside and at larger L shells (>6) on the dayside. In addition, very isotropic distributions at a few keV, which may be produced by Landau resonance and contribute to the formation of the typical gap in the chorus spectrum near 0.5 fce, are commonly observed on the dayside.
Kinetic‐size magnetic holes (KSMHs) in the turbulent magnetosheath are statistically investigated using high time resolution data from the Magnetospheric Multiscale mission. The KSMHs with short ...duration (i.e., <0.5 s) have their cross section smaller than the ion gyroradius. Superposed epoch analysis of all events reveals that an increase in the electron density and total temperature significantly increases (resp. decrease) the electron perpendicular (resp. parallel) temperature and an electron vortex inside KSMHs. Electron fluxes at ~90° pitch angles with selective energies increase in the KSMHs are trapped inside KSMHs and form the electron vortex due to their collective motion. All these features are consistent with the electron vortex magnetic holes obtained in 2‐D and 3‐D particle‐in‐cell simulations, indicating that the observed KSMHs seem to be best explained as electron vortex magnetic holes. It is furthermore shown that KSMHs are likely to heat and accelerate the electrons.
Key Points
Kinetic‐size magnetic holes are statistical investigated by MMS
Observed kinetic‐size magnetic holes seem to be best explained as electron vortex magnetic holes
Kinetic‐size magnetic holes are likely to heat and accelerate the electrons
Plain Language Summary
A nonlinear energy cascade in magnetized turbulent plasmas leads to the formation of different coherent structures which are thought to play an important role in dissipating energy and transporting particles. This study statistically investigate one new type of coherent structure, named electron vortex magnetic hole, used by Magnetospheric Multiscale data. It reveals the common features of this structure, including an increase in the electron density and total temperature, significantly increase (resp. decrease) the electron perpendicular (resp. parallel) temperature and an electron vortex inside these holes. The increase of electron temperature inside the holes indicates that these holes are likely to heat and accelerate the electrons. This gives new clue for energy dissipation in turbulent plasmas.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Using MMS high‐resolution measurements, we present the first observation of fast electron jet (Ve ~2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale ...comparable to the DF thickness (~ 0.9 di), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring‐current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron‐jet‐driven current (E ⋅ je ≈ 2 E ⋅ ji), rather than the ion current suggested in previous studies.
Key Points
For the first time, fast electron jet is observed at dipolarization front
This jet is responsible for current and energy conversion at dipolarization front
Quantitatively, the partition of energy conversion is E ⋅ je ≈ 2 E ⋅ ji
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A new type of electron-scale coherent structure, referred to as electron vortex magnetic holes, was identified recently in the Earth's magnetosheath turbulent plasma. These electron-scale magnetic ...holes are characterized by magnetic field strength depression, electron density enhancement, temperature and temperature anisotropy increase (a significant increase in perpendicular temperature and a decrease in parallel temperature), and an electron vortex formed by the trapped electrons. The strong increase of electron temperature indicates that these magnetic holes have a strong connection with the energization of electrons. Here, using high time resolution in situ measurements from the MMS mission, it is further shown that electron-scale whistler waves coexist with electron-scale magnetic holes. These whistler waves were found not propagating from remote regions, but generated locally due to electron temperature anisotropy (Te /Te ) inside the magnetic holes. This study provides new insights into the electron-scale plasma dynamics in turbulent plasmas.
The Search-Coil Magnetometer for MMS Le Contel, O.; Leroy, P.; Roux, A. ...
Space Science Reviews,
03/2016, Volume:
199, Issue:
1-4
Journal Article, Book Review
Peer reviewed
Open access
The tri-axial search-coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. (
2014
), this issue). It ...provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth’s magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conversion from magnetic to thermal and kinetic energies allowing local or global reconfigurations of the Earth’s magnetic field. The analog waveforms provided by the SCM are digitized and processed inside the digital signal processor (DSP), within the Central Electronics Box (CEB), together with the electric field data provided by the spin-plane double probe (SDP) and the axial double probe (ADP). On-board calibration signal provided by DSP allows the verification of the SCM transfer function once per orbit. Magnetic waveforms and on-board spectra computed by DSP are available at different time resolution depending on the selected mode. The SCM design is described in details as well as the different steps of the ground and in-flight calibrations.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Chorus waves, which have received intense attention recently due to their significant role in radiation belt electron dynamics, frequently exhibit rising and falling tones. Lower‐band chorus waves, ...observed using THEMIS wave burst data, are analyzed to obtain the typical properties of either class of chorus emissions. Our results show that rising tones are more likely to be quasi field‐aligned, whereas falling tones are typically very oblique, close to the resonance cone. Furthermore, rising tones occur significantly more often than falling tones, and magnetic amplitudes of rising tones are generally much larger than those of falling tones. We also show the preferential regions of rising and falling tones dependent on MLT and magnetic latitude. Our new findings suggest that two separate mechanisms may be responsible for the generation and nonlinear evolution of rising and falling tone chorus.
Key Points
Rising tones are quasi field‐aligned, while falling tones are very oblique
Wave amplitude of rising tones are larger than that of falling tones
The preferential region of rising and falling tones is dependent on MLT and MLAT
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Identifying the Driver of Pulsating Aurora Nishimura, Y; Bortnik, J; Li, W ...
Science (American Association for the Advancement of Science),
10/2010, Volume:
330, Issue:
6000
Journal Article
Peer reviewed
Pulsating aurora, a spectacular emission that appears as blinking of the upper atmosphere in the polar regions, is known to be excited by modulated, downward-streaming electrons. Despite its ...distinctive feature, identifying the driver of the electron precipitation has been a long-standing problem. Using coordinated satellite and ground-based all-sky imager observations from the THEMIS mission, we provide direct evidence that a naturally occurring electromagnetic wave, lower-band chorus, can drive pulsating aurora. Because the waves at a given equatorial location in space correlate with a single pulsating auroral patch in the upper atmosphere, our findings can also be used to constrain magnetic field models with much higher accuracy than has previously been possible.
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We describe methods for polynomial reconstruction of the magnetic field close to a cluster of spacecraft and apply that to reconstruction of the magnetic field observed during a magnetic reconnection ...event on 10 August 2017 by the Magnetospheric Multiscale spacecraft. Four different models are described, which vary in complexity between a 12‐parameter linear model, which has only linear variation with respect to the spatial coordinates, and a 27‐parameter quadratic model, which has the full quadratic expansion except that the second derivative with respect to the Minimum Directional Derivative minimum gradient coordinate
m has been neglected. In contrast to previous reconstruction techniques, these reconstructions can be found using only the magnetic field and current density measured at a single time by the cluster of spacecraft. The equations satisfying
∇·B=0 are satisfied exactly, while the equations specifying the model fields at the spacecraft locations are satisfied for most models in a best least squares sense. For this magnetotail event, the models have very small errors in magnetic field components (
<0.1 nT) at a distance from the nearest spacecraft on the order of the spacecraft separation,
Lsc, here equal to 20.5 km. The magnetic structures found using the quadratic models are very time dependent, with a stretched field leading to plasmoid formation at one point in time.
Key Points
Polynomial reconstruction methods using both magnetic field and particle current density for input are described
For a magnetotail event, the magnetic field error is small (
<0.1 nT) up to about one spacecraft separation from the nearest spacecraft
The quadratic reconstructions are very dynamic, with stretched magnetic fields leading to formation of plasmoids
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