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Sökning: WFRF:(Khotyaintsev Yu V.)

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1.
  • Carbone, F., et al. (författare)
  • Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere : Solar Orbiter observations
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The recently released spacecraft potential measured by the RPW instrument on board Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere. Aims. The measurement of the solar wind's electron density, taken in June 2020, has been analysed to obtain a thorough characterization of the turbulence and intermittency properties of the fluctuations. Magnetic field data have been used to describe the presence of ion-scale waves. Methods. To study and quantify the properties of turbulence, we extracted selected intervals. We used empirical mode decomposition to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, which additionally reduced issues typical of non-stationary, short time series. The presence of waves was quantitatively determined by introducing a parameter describing the time-dependent, frequency-filtered wave power. Results. A well-defined inertial range with power-law scalng was found almost everywhere in the sample studied. However, the Kolmogorov scaling and the typical intermittency effects are only present in fraction of the samples. Other intervals have shallower spectra and more irregular intermittency, which are not described by models of turbulence. These are observed predominantly during intervals of enhanced ion frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to give general context and help determine the cause of these anomalous fluctuations.
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2.
  • Graham, Daniel B., et al. (författare)
  • Kinetic electrostatic waves and their association with current structures in the solar wind
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. A variety of kinetic electrostatic and electromagnetic waves develop in the solar wind and the relationship between these waves and larger scale structures, such as current sheets and ongoing turbulence, remain a topic of investigation. Similarly, the instabilities producing ion-acoustic waves in the solar wind are still an open question. Aims. The goals of this paper are to investigate electrostatic Langmuir and ion-acoustic waves in the solar wind at 0.5 AU and determine whether current sheets and associated streaming instabilities can produce the observed waves. The relationship between these waves and currents observed in the solar wind is investigated statistically. Methods. Solar Orbiter's Radio and Plasma Waves instrument suite provides high-resolution snapshots of the fluctuating electric field. The Low Frequency Receiver resolves the waveforms of ion-acoustic waves and the Time Domain Sampler resolves the waveforms of both ion-acoustic and Langmuir waves. Using these waveform data, we determine when these waves are observed in relation to current structures in the solar wind, estimated from the background magnetic field. Results. Langmuir and ion-acoustic waves are frequently observed in the solar wind. Ion-acoustic waves are observed about 1% of the time at 0.5 AU. The waves are more likely to be observed in regions of enhanced currents. However, the waves typically do not occur at current structures themselves. The observed currents in the solar wind are too small to drive instability by the relative drift between single ion and electron populations. When multi-component ion or electron distributions are present, the observed currents may be sufficient for instabilities to occur. Ion beams are the most plausible source of ion-acoustic waves in the solar wind. The spacecraft potential is confirmed to be a reliable probe of the background electron density when comparing the peak frequencies of Langmuir waves with the plasma frequency calculated from the spacecraft potential.
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3.
  • Khotyaintsev, Yu, V, et al. (författare)
  • Density fluctuations associated with turbulence and waves First observations by Solar Orbiter
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. The aim of this work is to demonstrate that the probe-to-spacecraft potential measured by RPW on Solar Orbiter can be used to derive the plasma (electron) density measurement, which exhibits both a high temporal resolution and a high level of accuracy. To investigate the physical nature of the solar wind turbulence and waves, we analyze the density and magnetic field fluctuations around the proton cyclotron frequency observed by Solar Orbiter during the first perihelion encounter (similar to 0.5AU away from the Sun). Methods. We used the plasma density based on measurements of the probe-to-spacecraft potential in combination with magnetic field measurements by MAG to study the fields and density fluctuations in the solar wind. In particular, we used the polarization of the wave magnetic field, the phase between the compressible magnetic field and density fluctuations, and the compressibility ratio (the ratio of the normalized density fluctuations to the normalized compressible fluctuations of B) to characterize the observed waves and turbulence. Results. We find that the density fluctuations are 180 degrees out of phase (anticorrelated) with the compressible component of magnetic fluctuations for intervals of turbulence, whereas they are in phase for the circular-polarized waves. We analyze, in detail, two specific events with a simultaneous presence of left- and right-handed waves at di fferent frequencies. We compare the observed wave properties to a prediction of the three-fluid (electrons, protons, and alphas) model. We find a limit on the observed wavenumbers, 10(-6) < k < 7 > 10(-6) m(-1), which corresponds to a wavelength of 7 x 10(6) > lambda > 10(6) m. We conclude that it is most likely that both the leftand right-handed waves correspond to the low-wavenumber part (close to the cut-o ff at Omega(cHe++)) of the proton-band electromagnetic ion cyclotron (left-handed wave in the plasma frame confined to the frequency range Omega(cHe++) < omega < Omega(cp)) waves propagating in the outwards and inwards directions, respectively. The fact that both wave polarizations are observed at the same time and the identified wave mode has a low group velocity suggests that the double-banded events occur in the source regions of the waves.
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4.
  • Steinvall, Konrad, et al. (författare)
  • Solar wind current sheets and deHoffmann-Teller analysis First results from Solar Orbiter's DC electric field measurements
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Solar Orbiter was launched on 10 February 2020 with the purpose of investigating solar and heliospheric physics using a payload of instruments designed for both remote and in situ studies. Similar to the recently launched Parker Solar Probe, and unlike earlier missions, Solar Orbiter carries instruments designed to measure low-frequency DC electric fields. Aims. In this paper, we assess the quality of the low-frequency DC electric field measured by the Radio and Plasma Waves instrument (RPW) on Solar Orbiter. In particular, we investigate the possibility of using Solar Orbiter's DC electric and magnetic field data to estimate the solar wind speed. Methods. We used a deHoffmann-Teller (HT) analysis, based on measurements of the electric and magnetic fields, to find the velocity of solar wind current sheets, which minimises a single component of the electric field. By comparing the HT velocity to the proton velocity measured by the Proton and Alpha particle Sensor (PAS), we have developed a simple model for the effective antenna length, L-eff of the E-field probes. We then used the HT method to estimate the speed of the solar wind. Results. Using the HT method, we find that the observed variations in E-y are often in excellent agreement with the variations in the magnetic field. The magnitude of E-y, however, is uncertain due to the fact that the L-eff depends on the plasma environment. Here, we derive an empirical model relating L-eff to the Debye length, which we can use to improve the estimate of E-y and, consequently, the estimated solar wind speed. Conclusions. The low-frequency electric field provided by RPW is of high quality. Using the deHoffmann-Teller analysis, Solar Orbiter's magnetic and electric field measurements can be used to estimate the solar wind speed when plasma data are unavailable.
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5.
  • Soucek, J., et al. (författare)
  • Solar Orbiter Radio and Plasma Waves - Time Domain Sampler : In-flight performance and first results
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The Radio and Plasma Waves (RPW) instrument on board Solar Orbiter has been operating nearly continuously since the launch in February 2020. The Time Domain Sampler (TDS) receiver of the RPW instrument is dedicated to waveform measurements of plasma waves and dust impact signatures in an intermediate frequency range from 0.2 to 200 kHz. Aims. This article presents the first data from the RPW-TDS receiver and discusses the in-flight performance of the instrument and, in particular, the on-board wave and dust detection algorithm. We present the TDS data products and its scientific operation. We demonstrate the content of the dataset on several examples. In particular, we study the distribution of solar Langmuir waves in the first year of observations and one Type III burst event. Methods. The on-board detection algorithm is described in detail in this article and classifies the observed waveform snapshots, identifying plasma waves and dust impacts based on the ratio of their maximum amplitude to their median and on the spectral bandwidth. The algorithm allows TDS to downlink the most scientifically relevant waveforms and to perform an on-board statistical characterization of the processed data. Results. The detection algorithm of TDS is shown to perform very well in its detection of plasma waves and dust impacts with a high accuracy. The initial analysis of statistical data returned by TDS shows that sporadic Langmuir waves that are not associated with Type III events are routinely observed in the inner heliosphere, with a clear increase in occurrence rate closer to the Sun. We also present an example of RPW observations during an encounter of the source region of a Type III burst, which exploits the on-board calculated histograms data.
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6.
  • Vecchio, A., et al. (författare)
  • Solar Orbiter/RPW antenna calibration in the radio domain and its application to type III burst observations
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656, s. A33-
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. In order to allow for a comparison with the measurements from other antenna systems, the voltage power spectral density measured by the Radio and Plasma waves receiver (RPW) on board Solar Orbiter needs to be converted into physical quantities that depend on the intrinsic properties of the radiation itself (e.g., the brightness of the source). Aims. The main goal of this study is to perform a calibration of the RPW dipole antenna system that allows for the conversion of the voltage power spectral density measured at the receiver's input into the incoming flux density. Methods. We used space observations from the Thermal Noise Receiver (TNR) and the High Frequency Receiver (HFR) to perform the calibration of the RPW dipole antenna system. Observations of type III bursts by the Wind spacecraft are used to obtain a reference radio flux density for cross-calibrating the RPW dipole antennas. The analysis of a large sample of HFR observations (over about ten months), carried out jointly with an analysis of TNR-HFR data and prior to the antennas' deployment, allowed us to estimate the reference system noise of the TNR-HFR receivers. Results. We obtained the effective length, l(eff), of the RPW dipoles and the reference system noise of TNR-HFR in space, where the antennas and pre-amplifiers are embedded in the solar wind plasma. The obtained l(eff) values are in agreement with the simulation and measurements performed on the ground. By investigating the radio flux intensities of 35 type III bursts simultaneously observed by Wind and Solar Orbiter, we found that while the scaling of the decay time as a function of the frequency is the same for the Waves and RPW instruments, their median values are higher for the former. This provides the first observational evidence that Type III radio waves still undergo density scattering, even when they propagate from the source, in a medium with a plasma frequency that is well below their own emission frequency.
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7.
  • Burch, J. L., et al. (författare)
  • Electron-scale measurements of magnetic reconnection in space
  • 2016
  • Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 352:6290, s. 1189-
  • Forskningsöversikt (refereegranskat)abstract
    • Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.
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8.
  • Dimmock, A. P., et al. (författare)
  • Analysis of multiscale structures at the quasi-perpendicular Venus bow shock Results from Solar Orbiter's first Venus flyby
  • 2022
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 660
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Solar Orbiter is a European Space Agency mission with a suite of in situ and remote sensing instruments to investigate the physical processes across the inner heliosphere. During the mission, the spacecraft is expected to perform multiple Venus gravity assist maneuvers while providing measurements of the Venusian plasma environment. The first of these occurred on 27 December 2020, in which the spacecraft measured the regions such as the distant and near Venus magnetotail, magnetosheath, and bow shock. Aims. This study aims to investigate the outbound Venus bow shock crossing measured by Solar Orbiter during the first flyby. We study the complex features of the bow shock traversal in which multiple large amplitude magnetic field and density structures were observed as well as higher frequency waves. Our aim is to understand the physical mechanisms responsible for these high amplitude structures, characterize the higher frequency waves, determine the source of the waves, and put these results into context with terrestrial bow shock observations. Methods. High cadence magnetic field, electric field, and electron density measurements were employed to characterize the properties of the large amplitude structures and identify the relevant physical process. Minimum variance analysis, theoretical shock descriptions, coherency analysis, and singular value decomposition were used to study the properties of the higher frequency waves to compare and identify the wave mode. Results. The non-planar features of the bow shock are consistent with shock rippling and/or large amplitude whistler waves. Higher frequency waves are identified as whistler-mode waves, but their properties across the shock imply they may be generated by electron beams and temperature anisotropies. Conclusions. The Venus bow shock at a moderately high Mach number (similar to 5) in the quasi-perpendicular regime exhibits complex features similar to the Earth's bow shock at comparable Mach numbers. The study highlights the need to be able to distinguish between large amplitude waves and spatial structures such as shock rippling. The simultaneous high frequency observations also demonstrate the complex nature of energy dissipation at the shock and the important question of understanding cross-scale coupling in these complex regions. These observations will be important to interpreting future planetary missions and additional gravity assist maneuvers.
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9.
  • Lotekar, A., et al. (författare)
  • Multisatellite MMS Analysis of Electron Holes in the Earth's Magnetotail : Origin, Properties, Velocity Gap, and Transverse Instability
  • 2020
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a statistical analysis of more than 2,400 electrostatic solitary waves interpreted as electron holes (EH) measured aboard at least three Magnetospheric Multiscale (MMS) spacecraft in the Earth's magnetotail. The velocities of EHs are estimated using the multispacecraft interferometry. The EH velocities in the plasma rest frame are in the range from just a few km/s, which is much smaller than ion thermal velocity V-Ti, up to 20,000 km/s, which is comparable to electron thermal velocity V-Te. We argue that fast EHs with velocities larger than about 0.1V(Te) are produced by bump-on-tail instabilities, while slow EHs with velocities below about 0.05V(Te) can be produced by warm bistream and, probably, Buneman-type instabilities. We show that typically fast and slow EHs do not coexist, indicating that the instabilities producing EHs of different types operate independently. We have identified a gap in the distribution of EH velocities between V-Ti and 2V(Ti), which is considered to be the evidence for self-acceleration (Zhou & Hutchinson, 2018) or ion Landau damping of EHs. Parallel spatial scales and amplitudes of EHs are typically between lambda(D) and 10 lambda(D) and between 10(-3) T-e and 0.1 T-e, respectively. We show that electrostatic potential amplitudes of EHs are below the threshold of the transverse instability and highly likely restricted by the nonlinear saturation criterion of electron streaming instabilities seeding electron hole formation: e Phi(0)less than or similar to me pi(2)d(parallel to)(2), where pi = min(gamma, 1.5 omega(ce)), where gamma is the increment of instabilities seeding EH formation, while pi(ce) is electron cyclotron frequency. The implications of the presented results are discussed.
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10.
  • Wilder, F. D., et al. (författare)
  • Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
  • 2016
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:12, s. 5909-5917
  • Tidskriftsartikel (refereegranskat)abstract
    • We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data.
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11.
  • Alqeeq, S. W., et al. (författare)
  • Two Classes of Equatorial Magnetotail Dipolarization Fronts Observed by Magnetospheric Multiscale Mission : A Statistical Overview
  • 2023
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We carried out a statistical study of equatorial dipolarization fronts (DFs) detected by the Magnetospheric Multiscale mission during the full 2017 Earth's magnetotail season. We found that two DF classes are distinguished: class I (74.4%) corresponds to the standard DF properties and energy dissipation and a new class II (25.6%). This new class includes the six DF discussed in Alqeeq et al. (2022, ) and corresponds to a bump of the magnetic field associated with a minimum in the ion and electron pressures and a reversal of the energy conversion process. The possible origin of this second class is discussed. Both DF classes show that the energy conversion process in the spacecraft frame is driven by the diamagnetic current dominated by the ion pressure gradient. In the fluid frame, it is driven by the electron pressure gradient. In addition, we have shown that the energy conversion processes are not homogeneous at the electron scale mostly due to the variations of the electric fields for both DF classes.
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12.
  • André, Mats, et al. (författare)
  • Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause
  • 2016
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6705-6712
  • Tidskriftsartikel (refereegranskat)abstract
    • Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.
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13.
  • Argall, M. R., et al. (författare)
  • Electron Dynamics Within the Electron Diffusion Region of Asymmetric Reconnection
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:1, s. 146-162
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the agyrotropic nature of electron distribution functions and their substructure to illuminate electron dynamics in a previously reported electron diffusion region (EDR) event. In particular, agyrotropy is examined as a function of energy to reveal detailed finite Larmor radius effects for the first time. It is shown that the previously reported approximate to 66eV agyrotropic "crescent" population that has been accelerated as a result of reconnection is evanescent in nature because it mixes with a denser, gyrotopic background. Meanwhile, accelerated agyrotropic populations at 250 and 500eV are more prominent because the background plasma at those energies is more tenuous. Agyrotropy at 250 and 500eV is also more persistent than at 66eV because of finite Larmor radius effects; agyrotropy is observed 2.5 ion inertial lengths from the EDR at 500eV, but only in close proximity to the EDR at 66eV. We also observe linearly polarized electrostatic waves leading up to and within the EDR. They have wave normal angles near 90 degrees, and their occurrence and intensity correlate with agyrotropy. Within the EDR, they modulate the flux of 500eV electrons travelling along the current layer. The net electric field intensifies the reconnection current, resulting in a flow of energy from the fields into the plasma. Plain Language Summary The process of reconnection involves an explosive transfer of magnetic energy into particle energy. When energetic particles contact modern technology such as satellites, cell phones, or other electronic devices, they can cause random errors and failures. Exactly how particles are energized via reconnection, however, is still unknown. Fortunately, the Magnetospheric Multiscale mission is finally able to detect and analyze reconnection processes. One recent finding is that energized particles take on a crescent-shaped configuration in the vicinity of reconnection and that this crescent shape is related to the energy conversion process. In our paper, we explain why the crescent shape has not been observed until now and inspect particle motions to determine what impact it has on energy conversion. When reconnection heats the plasma, the crescent shape forms from the cool, tenuous particles. As plasmas from different regions mix, dense, nonheated plasma obscures the crescent shape in our observations. The highest-energy particle population created by reconnection, though, also contains features of the crescent shape that are more persistent but appear less dramatically in the data.
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14.
  • Breuillard, H., et al. (författare)
  • Multispacecraft analysis of dipolarization fronts and associated whistler wave emissions using MMS data
  • 2016
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:14, s. 7279-7286
  • Tidskriftsartikel (refereegranskat)abstract
    • Dipolarization fronts (DFs), embedded in bursty bulk flows, play a crucial role in Earth's plasma sheet dynamics because the energy input from the solar wind is partly dissipated in their vicinity. This dissipation is in the form of strong low-frequency waves that can heat and accelerate energetic electrons up to the high-latitude plasma sheet. However, the dynamics of DF propagation and associated low-frequency waves in the magnetotail are still under debate due to instrumental limitations and spacecraft separation distances. In May 2015 the Magnetospheric Multiscale (MMS) mission was in a string-of-pearls configuration with an average intersatellite distance of 160km, which allows us to study in detail the microphysics of DFs. Thus, in this letter we employ MMS data to investigate the properties of dipolarization fronts propagating earthward and associated whistler mode wave emissions. We show that the spatial dynamics of DFs are below the ion gyroradius scale in this region (approximate to 500km), which can modify the dynamics of ions in the vicinity of the DF (e.g., making their motion nonadiabatic). We also show that whistler wave dynamics have a temporal scale of the order of the ion gyroperiod (a few seconds), indicating that the perpendicular temperature anisotropy can vary on such time scales.
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15.
  • Breuillard, H., et al. (författare)
  • New Insights into the Nature of Turbulence in the Earth's Magnetosheath Using Magnetospheric MultiScale Mission Data
  • 2018
  • Ingår i: Astrophysical Journal. - : IOP PUBLISHING LTD. - 0004-637X .- 1538-4357. ; 859:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The Earth's magnetosheath, which is characterized by highly turbulent fluctuations, is usually divided into two regions of different properties as a function of the angle between the interplanetary magnetic field and the shock normal. In this study, we make use of high-time resolution instruments on board the Magnetospheric MultiScale spacecraft to determine and compare the properties of subsolar magnetosheath turbulence in both regions, i. e., downstream of the quasi-parallel and quasi-perpendicular bow shocks. In particular, we take advantage of the unprecedented temporal resolution of the Fast Plasma Investigation instrument to show the density fluctuations down to sub-ion scales for the first time. We show that the nature of turbulence is highly compressible down to electron scales, particularly in the quasi-parallel magnetosheath. In this region, the magnetic turbulence also shows an inertial (Kolmogorov-like) range, indicating that the fluctuations are not formed locally, in contrast with the quasi-perpendicular magnetosheath. We also show that the electromagnetic turbulence is dominated by electric fluctuations at sub-ion scales (f > 1Hz) and that magnetic and electric spectra steepen at the largest-electron scale. The latter indicates a change in the nature of turbulence at electron scales. Finally, we show that the electric fluctuations around the electron gyrofrequency are mostly parallel in the quasi-perpendicular magnetosheath, where intense whistlers are observed. This result suggests that energy dissipation, plasma heating, and acceleration might be driven by intense electrostatic parallel structures/waves, which can be linked to whistler waves.
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16.
  • Breuillard, H., et al. (författare)
  • The Properties of Lion Roars and Electron Dynamics in Mirror Mode Waves Observed by the Magnetospheric MultiScale Mission
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:1, s. 93-103
  • Tidskriftsartikel (refereegranskat)abstract
    • Mirror mode waves are ubiquitous in the Earth's magnetosheath, in particular behind the quasi-perpendicular shock. Embedded in these nonlinear structures, intense lion roars are often observed. Lion roars are characterized by whistler wave packets at a frequency similar to 100Hz, which are thought to be generated in the magnetic field minima. In this study, we make use of the high time resolution instruments on board the Magnetospheric MultiScale mission to investigate these waves and the associated electron dynamics in the quasi-perpendicular magnetosheath on 22 January 2016. We show that despite a core electron parallel anisotropy, lion roars can be generated locally in the range 0.05-0.2f(ce) by the perpendicular anisotropy of electrons in a particular energy range. We also show that intense lion roars can be observed up to higher frequencies due to the sharp nonlinear peaks of the signal, which appear as sharp spikes in the dynamic spectra. As a result, a high sampling rate is needed to estimate correctly their amplitude, and the latter might have been underestimated in previous studies using lower time resolution instruments. We also present for the first-time 3-D high time resolution electron velocity distribution functions in mirror modes. We demonstrate that the dynamics of electrons trapped in the mirror mode structures are consistent with the Kivelson and Southwood (1996) model. However, these electrons can also interact with the embedded lion roars: first signatures of electron quasi-linear pitch angle diffusion and possible signatures of nonlinear interaction with high-amplitude wave packets are presented. These processes can lead to electron untrapping from mirror modes.
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17.
  • Chen, L. -J, et al. (författare)
  • Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock
  • 2018
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 120:22
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating. 
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18.
  • Chen, L-J, et al. (författare)
  • Lower-Hybrid Drift Waves Driving Electron Nongyrotropic Heating and Vortical Flows in a Magnetic Reconnection Layer
  • 2020
  • Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 125:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We report measurements of lower-hybrid drift waves driving electron heating and vortical flows in an electron-scale reconnection layer under a guide field. Electrons accelerated by the electrostatic potential of the waves exhibit perpendicular and nongyrotropic heating. The vortical flows generate magnetic field perturbations comparable to the guide field magnitude. The measurements reveal a new regime of electron-wave interaction and how this interaction modifies the electron dynamics in the reconnection layer.
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19.
  • Cozzani, Giulia, et al. (författare)
  • Structure of a Perturbed Magnetic Reconnection Electron Diffusion Region in the Earth's Magnetotail
  • 2021
  • Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 127:21
  • Tidskriftsartikel (refereegranskat)abstract
    • We report in situ observations of an electron diffusion region (EDR) and adjacent separatrix region in the Earth's magnetotail. We observe significant magnetic field oscillations near the lower hybrid frequency which propagate perpendicularly to the reconnection plane. We also find that the strong electron-scale gradients close to the EDR exhibit significant oscillations at a similar frequency. Such oscillations are not expected for a crossing of a steady 2D EDR, and can be explained by a complex motion of the reconnection plane induced by current sheet kinking propagating in the out-of-reconnection-plane direction. Thus, all three spatial dimensions have to be taken into account to explain the observed perturbed EDR crossing. These results shed light on the interplay between magnetic reconnection and current sheet drift instabilities in electron-scale current sheets and highlight the need for adopting a 3D description of the EDR, going beyond the two-dimensional and steady-state conception of reconnection.
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20.
  • Dimmock, Andrew P., et al. (författare)
  • Mirror Mode Storms Observed by Solar Orbiter
  • 2022
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Mirror modes (MMs) are ubiquitous in space plasma and grow from pressure anisotropy. Together with other instabilities, they play a fundamental role in constraining the free energy contained in the plasma. This study focuses on MMs observed in the solar wind by Solar Orbiter (SolO) for heliocentric distances between 0.5 and 1 AU. Typically, MMs have timescales from several to tens of seconds and are considered quasi-MHD structures. In the solar wind, they also generally appear as isolated structures. However, in certain conditions, prolonged and bursty trains of higher frequency MMs are measured, which have been labeled previously as MM storms. At present, only a handful of existing studies have focused on MM storms, meaning that many open questions remain. In this study, SolO has been used to investigate several key aspects of MM storms: their dependence on heliocentric distance, association with local plasma properties, temporal/spatial scale, amplitude, and connections with larger-scale solar wind transients. The main results are that MM storms often approach local ion scales and can no longer be treated as quasi-magnetohydrodynamic, thus breaking the commonly used long-wavelength assumption. They are typically observed close to current sheets and downstream of interplanetary shocks. The events were observed during slow solar wind speeds and there was a tendency for higher occurrence closer to the Sun. The occurrence is low, so they do not play a fundamental role in regulating ambient solar wind but may play a larger role inside transients.
  •  
21.
  • Divin, A., et al. (författare)
  • Evolution of the lower hybrid drift instability at reconnection jet front
  • 2015
  • Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:4, s. 2675-2690
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate current-driven modes developing at jet fronts during collisionless reconnection. Initial evolution of the reconnection is simulated using conventional 2-D setup starting from the Harris equilibrium. Three-dimensional PIC calculations are implemented at later stages, when fronts are fully formed. Intense currents and enhanced wave activity are generated at the fronts because of the interaction of the fast flow plasma and denser ambient current sheet plasma. The study reveals that the lower hybrid drift instability develops quickly in the 3-D simulation. The instability produces strong localized perpendicular electric fields, which are several times larger than the convective electric field at the front, in agreement with Time History of Events and Macroscale Interactions during Substorms observations. The instability generates waves, which escape the front edge and propagate into the undisturbed plasma ahead of the front. The parallel electron pressure is substantially larger in the 3-D simulation compared to that of the 2-D. In a time similar to Omega(-1)(ci), the instability forms a layer, which contains a mixture of the jet plasma and current sheet plasma. The results confirm that the lower hybrid drift instability is important for the front evolution and electron energization.
  •  
22.
  • Eriksson, S., et al. (författare)
  • Magnetospheric Multiscale observations of magnetic reconnection associated with Kelvin-Helmholtz waves
  • 2016
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:11, s. 5606-5615
  • Tidskriftsartikel (refereegranskat)abstract
    • The four Magnetospheric Multiscale (MMS) spacecraft recorded the first direct evidence of reconnection exhausts associated with Kelvin-Helmholtz (KH) waves at the duskside magnetopause on 8 September 2015 which allows for local mass and energy transport across the flank magnetopause. Pressure anisotropy-weighted Walen analyses confirmed in-plane exhausts across 22 of 42 KH-related trailing magnetopause current sheets (CSs). Twenty-one jets were observed by all spacecraft, with small variations in ion velocity, along the same sunward or antisunward direction with nearly equal probability. One exhaust was only observed by the MMS-1,2 pair, while MMS-3,4 traversed a narrow CS (1.5 ion inertial length) in the vicinity of an electron diffusion region. The exhausts were locally 2-D planar in nature as MMS-1,2 observed almost identical signatures separated along the guide-field. Asymmetric magnetic and electric Hall fields are reported in agreement with a strong guide-field and a weak plasma density asymmetry across the magnetopause CS.
  •  
23.
  • Gao, C. -H, et al. (författare)
  • Effect of the Electric Field on the Agyrotropic Electron Distributions
  • 2021
  • Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 48:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate agyrotropic electron distributions from two magnetopause events observed by magnetospheric multiscale (MMS) spacecraft. Agyrotropic electron distributions can be generated by the finite electron gyration at an electron-scale boundary, and the electric field normal to this boundary usually contributes to the electron acceleration to make the agyrotropic distributions more apparent. The effect of the electric field becomes important only when it is sufficiently strong and local, meaning its electrostatic potential is comparable to or larger than the electron temperature, and its width is smaller than the electron thermal gyroradius, so that this electric field can directly accelerate part of the electrons out of the original core to form agyrotropic electron distributions. Also, we reproduce the measured electron "finger" structures from test particle simulations, which can be effectively suppressed by increasing the sampling rate of the electron measurement. Plain Language Summary Agyrotropic electron distributions reveal valuable information of electron dynamics at electron scales, and the generation of these distributions have been extensively studied. In this study, we provide a new possibility to generate agyrotropic electron distributions with a strong localized electric field, which can accelerate part of electrons out of the original electron core to form agyrotropic distributions. As such large-amplitude small-scale electric field fluctuations are frequently observed in turbulent plasma environments, we suggest that more agyrotropic electron distributions can be observed with high temporal resolution measurements.
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24.
  • Graham, D. B., et al. (författare)
  • Direct observations of anomalous resistivity and diffusion in collisionless plasma
  • 2022
  • Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Coulomb collisions provide plasma resistivity and diffusion but in many low-density astrophysical plasmas such collisions between particles are extremely rare. Scattering of particles by electromagnetic waves can lower the plasma conductivity. Such anomalous resistivity due to wave-particle interactions could be crucial to many processes, including magnetic reconnection. It has been suggested that waves provide both diffusion and resistivity, which can support the reconnection electric field, but this requires direct observation to confirm. Here, we directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves using measurements from the four Magnetospheric Multiscale (MMS) spacecraft. We show that anomalous resistivity is approximately balanced by anomalous viscosity, and thus the waves do not contribute to the reconnection electric field. However, the waves do produce an anomalous electron drift and diffusion across the current layer associated with magnetic reconnection. This leads to relaxation of density gradients at timescales of order the ion cyclotron period, and hence modifies the reconnection process. It is suggested that waves can provide both diffusion and resistivity that can potentially support the reconnection electric field in low-density astrophysical plasmas. Here, the authors show, using direct spacecraft measurements, that the waves contribute to anomalous diffusion but do not contribute to the reconnection electric field.
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25.
  • Graham, Daniel B., et al. (författare)
  • Electron currents and heating in the ion diffusion region of asymmetric reconnection
  • 2016
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 43:10, s. 4691-4700
  • Tidskriftsartikel (refereegranskat)abstract
    • In this letter the structure of the ion diffusion region of magnetic reconnection at Earth's magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.
  •  
26.
  • Graham, Daniel B., et al. (författare)
  • Enhanced Escape of Spacecraft Photoelectrons Caused by Langmuir and Upper Hybrid Waves
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:9, s. 7534-7553
  • Tidskriftsartikel (refereegranskat)abstract
    • The spacecraft potential is often used to infer rapid changes in the thermal plasma density. The variations in spacecraft potential associated with large-amplitude Langmuir and upper hybrid waves are investigated with the Magnetospheric Multiscale (MMS) mission. When large-amplitude Langmuir and upper hybrid waves are observed, the spacecraft potential increases. The changes in spacecraft potential are shown to be due to enhanced photoelectron escape from the spacecraft when the wave electric fields reach large amplitude. The fluctuations in spacecraft potential follow the envelope function of the Langmuir and upper hybrid waves. Comparison with the high-resolution electron moments shows that the changes in spacecraft potential associated with the waves are not due to density perturbations. Indeed, using the spacecraft potential as a density probe leads to unphysically large density fluctuations. In addition, the changes in spacecraft potential are shown to increase as density decreases: larger spacecraft potential changes are observed in the magnetosphere, than in the magnetosheath and solar wind. These results show that external electric fields can lead to unphysical results when the spacecraft potential is used as a density probe. The results suggest that fluctuations in the spacecraft potential alone cannot be used to determine whether nonlinear processes associated with Langmuir and upper hybrid waves, such as the ponderomotive force and three-wave decay, are occurring.
  •  
27.
  • Graham, Daniel B., et al. (författare)
  • Instability of Agyrotropic Electron Beams near the Electron Diffusion Region
  • 2017
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 119:2
  • Tidskriftsartikel (refereegranskat)abstract
    • During a magnetopause crossing the Magnetospheric Multiscale spacecraft encountered an electron diffusion region (EDR) of asymmetric reconnection. The EDR is characterized by agyrotropic beam and crescent electron distributions perpendicular to the magnetic field. Intense upper-hybrid (UH) waves are found at the boundary between the EDR and magnetosheath inflow region. The UH waves are generated by the agyrotropic electron beams. The UH waves are sufficiently large to contribute to electron diffusion and scattering, and are a potential source of radio emission near the EDR. These results provide observational evidence of wave-particle interactions at an EDR, and suggest that waves play an important role in determining the electron dynamics.
  •  
28.
  • Graham, Daniel B., et al. (författare)
  • Large-Amplitude High-Frequency Waves at Earth's Magnetopause
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:4, s. 2630-2657
  • Tidskriftsartikel (refereegranskat)abstract
    • 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 1Vm(-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.
  •  
29.
  • Graham, Daniel B., et al. (författare)
  • Lower hybrid waves in the ion diffusion and magnetospheric inflow regions
  • 2017
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:1, s. 517-533
  • Tidskriftsartikel (refereegranskat)abstract
    • The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion-ion cross-field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross-field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.
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30.
  • Johlander, Andreas, 1990-, et al. (författare)
  • Ion Acceleration Efficiency at the Earth's Bow Shock : Observations and Simulation Results
  • 2021
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 914:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Collisionless shocks are some of the most efficient particle accelerators in heliospheric and astrophysical plasmas. Here we study and quantify ion acceleration at Earth's bow shock with observations from NASA's Magnetospheric Multiscale (MMS) satellites and in a global hybrid-Vlasov simulation. From the MMS observations, we find that quasiparallel shocks are more efficient at accelerating ions. There, up to 15% of the available energy goes into accelerating ions above 10 times their initial energy. Above a shock-normal angle of similar to 50 degrees, essentially no energetic ions are observed downstream of the shock. We find that ion acceleration efficiency is significantly lower when the shock has a low Mach number (M ( A ) < 6) while there is little Mach number dependence for higher values. We also find that ion acceleration is lower on the flanks of the bow shock than at the subsolar point regardless of the Mach number. The observations show that a higher connection time of an upstream field line leads to somewhat higher acceleration efficiency. To complement the observations, we perform a global hybrid-Vlasov simulation with realistic solar-wind parameters with the shape and size of the bow shock. We find that the ion acceleration efficiency in the simulation shows good quantitative agreement with the MMS observations. With the combined approach of direct spacecraft observations, we quantify ion acceleration in a wide range of shock angles and Mach numbers.
  •  
31.
  • Johlander, Andreas, et al. (författare)
  • Rippled Quasiperpendicular Shock Observed by the Magnetospheric Multiscale Spacecraft
  • 2016
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 117:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Collisionless shock nonstationarity arising from microscale physics influences shock structure and particle acceleration mechanisms. Nonstationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely spaced (subgyroscale), high-time-resolution measurements from one rapid crossing of Earth's quasiperpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing nonstationarity processes. Using MMS's high-cadence kinetic plasma measurements, we show that the shock exhibits nonstationarity in the form of ripples.
  •  
32.
  • Khotyaintsev, Yu, V, et al. (författare)
  • Electron Heating by Debye-Scale Turbulence in Guide-Field Reconnection
  • 2020
  • Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 124:4
  • Tidskriftsartikel (refereegranskat)abstract
    • We report electrostatic Debye-scale turbulence developing within the diffusion region of asymmetric magnetopause reconnection with amoderate guide field using observations by the Magnetospheric Multiscale mission. We show that Buneman waves and beam modes cause efficient and fast thermalization of the reconnection electron jet by irreversible phase mixing, during which the jet kinetic energy is transferred into thermal energy. Our results show that the reconnection diffusion region in the presence of a moderate guide field is highly turbulent, and that electrostatic turbulence plays an important role in electron heating.
  •  
33.
  • Khotyaintsev, Yuri V., et al. (författare)
  • Energy conversion at dipolarization fronts
  • 2017
  • Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 44:3, s. 1234-1242
  • Tidskriftsartikel (refereegranskat)abstract
    • We use multispacecraft observations by Cluster in the Earth's magnetotail and 3-D particle-in-cell simulations to investigate conversion of electromagnetic energy at the front of a fast plasma jet. We find that the major energy conversion is happening in the Earth (laboratory) frame, where the electromagnetic energy is being transferred from the electromagnetic field to particles. This process operates in a region with size of the order several ion inertial lengths across the jet front, and the primary contribution to E . j is coming from the motional electric field and the ion current. In the frame of the front we find fluctuating energy conversion with localized loads and generators at sub-ion scales which are primarily related to the lower hybrid drift instability excited at the front; however, these provide relatively small net energy conversion.
  •  
34.
  • Le Contel, O., et al. (författare)
  • Lower Hybrid Drift Waves and Electromagnetic Electron Space-Phase Holes Associated With Dipolarization Fronts and Field-Aligned Currents Observed by the Magnetospheric Multiscale Mission During a Substorm
  • 2017
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:12, s. 12236-12257
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyze two ion scale dipolarization fronts associated with field-aligned currents detected by the Magnetospheric Multiscale mission during a large substorm on 10 August 2016. The first event corresponds to a fast dawnward flow with an antiparallel current and could be generated by the wake of a previous fast earthward flow. It is associated with intense lower hybrid drift waves detected at the front and propagating dawnward with a perpendicular phase speed close to the electric drift and the ion thermal velocity. The second event corresponds to a flow reversal: from southwward/dawnward to northward/duskward associated with a parallel current consistent with a brief expansion of the plasma sheet before the front crossing and with a smaller lower hybrid drift wave activity. Electromagnetic electron phase-space holes are detected near these low-frequency drift waves during both events. The drift waves could accelerate electrons parallel to the magnetic field and produce the parallel electron drift needed to generate the electron holes. Yet we cannot rule out the possibility that the drift waves are produced by the antiparallel current associated with the fast flows, leaving the source for the electron holes unexplained.
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35.
  • Li, Wenya, et al. (författare)
  • Upper-Hybrid Waves Driven by Meandering Electrons Around Magnetic Reconnection X Line
  • 2021
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:16
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetic reconnection is a fundamental process in collisionless space plasma environment, and plasma waves relevant to the kinetic interactions can have a significant impact on the multiscale behavior of reconnection. Here, we present Magnetospheric Multiscale (MMS) observations during an encounter of an X line of symmetric magnetic reconnection in the magnetotail. The X line is characterized by reversals of ion and electron jets and electromagnetic fields, agyrotropic electron velocity distribution functions (VDFs), and an electron-scale current sheet. MMS observe large-amplitude nonlinear upper-hybrid (UH) waves on both sides of the neutral line, and the wave amplitudes have highly localized distribution along the normal direction. The inbound meandering electrons drive the UH waves, releasing the free energy stored from the reconnection electric field along the meandering trajectories. The interaction between the meandering electrons and the UH waves may modify the balance of the reconnection electric field around the X line. Plain Language Summary The electron-scale kinetic physics in the electron diffusion region (EDR) controls how magnetic field lines break and reconnect. Electron crescent, an indicator of EDR, can drive high-frequency electrostatic waves around EDR. For the first time, the upper-hybrid (UH) waves are observed on both sides of the X line and we show the direct association between the UH waves and the reconnection electric field. The strong wave-electron interaction can change the electron-scale dynamics and may modify the reconnection electric field. This study demonstrates that the UH waves may play an important role in controlling the reconnection rate.
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36.
  • Matsui, H., et al. (författare)
  • A Multi-Instrument Study of a Dipolarization Event in the Inner Magnetosphere
  • 2021
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:5
  • Tidskriftsartikel (refereegranskat)abstract
    • A dipolarization of the background magnetic field was observed during a conjunction of the Magnetospheric Multiscale (MMS) spacecraft and Van Allen Probe B on September 22, 2018. The spacecraft were located in the inner magnetosphere at L similar to 6-7 just before midnight magnetic local time (MLT). The radial separation between MMS and Probe B was similar to 1R(E). Gradual dipolarization or an increase of the northward component B-Z of the background field occurred on a timescale of minutes. Exploration of energization and Radiation in Geospace located 0.5 MLT eastward at a similar L shell also measured a gradual increase. The spatial scale was of the order of 1 R-E. On top of that, MMS and Probe B measured B-Z increases, and a decrease in one case, on a timescale of seconds, accompanied by large electric fields with amplitudes > several tens of mV/m. Spatial scale lengths were of the order of the ion inertial length and the ion gyroradius. The inertial term in the momentum equation and the Hall term in the generalized Ohm's law were sometimes non-negligible. These small-scale variations are discussed in terms of the ballooning/interchange instability and kinetic Alfven waves among others. It is inferred that physics of multiple scales was involved in the dynamics of this dipolarization event.
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37.
  • Matsui, H., et al. (författare)
  • Characteristics of storm time electric fields in the inner magnetosphere derived from Cluster data
  • 2010
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 115, s. A11215-
  • Tidskriftsartikel (refereegranskat)abstract
    • Storm-time electric fields in the inner magnetosphere measured by Cluster are reported in this study. First, we show two events around the time when Dst index is at a minimum. The electric field possibly related to subauroral ion drifts and/or undershielding is measured inside the inner edge of the electron plasma sheet in the eveningside. For the second event observed in the nightside, the electric field is partly related to dipolarization and is considered as inductive. An electric field without coincident magnetic signatures is also observed. Spatial coherence of the electric field is not large when we check multispacecraft data. It is inferred that the electric field in the magnetotail penetrates inside the region 1 current, while it is not clear about the electric field within the region 2 current from our data. Then superposed epoch analyses using 71 storms are performed. Electric fields at R = 3.5-6R(E) and less than 25 degrees of magnetic latitudes are enhanced around the minimum Dst at all magnetic local times. Electric fields during the recovery phase decay on a time scale shorter than that of Dst index, which could be interpreted in terms of the relation between electric field and ring current during that storm phase. AC electric fields are generally larger than DC electric fields, indicating that the former component might play some role in accelerating ring current particles. These results will be useful to update our empirical electric field model.
  •  
38.
  • Matsui, H., et al. (författare)
  • Dipolarization in the inner magnetosphere during a geomagnetic storm on 7 October 2015
  • 2016
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 43:18, s. 9397-9405
  • Tidskriftsartikel (refereegranskat)abstract
    • A dipolarization event was observed by the Magnetospheric Multiscale (MMS) spacecraft at L = 3.8 and 19.8 magnetic local time starting at similar to 23:42:36 UT on 7 October 2015. The magnetic and electric fields showed initially coherent variations between the spacecraft. The sunward convection turned tailward after the dipolarization. The observation is interpreted in terms of the pressure balance or the momentum equation. This was followed by a region traversed where the fields were irregular. The scale length was of the order of the ion gyroradius, suggesting the kinetic nature of the fluctuations. Combination of the multi-instrument, multispacecraft data reveals a more detailed picture of the dipolarization event in the inner magnetosphere. Conjunction ionosphere-plasmasphere observations from DMSP, two-dimensional GPS total electron content, the Millstone Hill midlatitude incoherent scatter radar, and AMPERE measurements imply that MMS observations are located on the poleward edge of the ionospheric trough where Region 2 field-aligned currents flow.
  •  
39.
  • Matsui, H., et al. (författare)
  • Multi-spacecraft observations of small-scale fluctuations in density and fields in plasmaspheric plumes
  • 2012
  • Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 30:3, s. 623-637
  • Tidskriftsartikel (refereegranskat)abstract
    • In this event study, small-scale fluctuations in plasmaspheric plumes with time scales of similar to 10 s to minutes in the spacecraft frame are examined. In one event, plasmaspheric plumes are observed by Cluster, while IMAGE measured density enhancement at a similar location. Fluctuations in density exist in plumes as detected by Cluster and are accompanied by fluctuations in magnetic fields and electric fields. Magnetic fluctuations are transverse and along the direction of the plumes. The E/B ratio is smaller than the Alfv,n velocity. Another similar event is briefly presented. We then consider physical properties of the fluctuations. Alfv,n mode modulated by the feedback instability is one possibility, although non-local generation is likely. It is hard to show that the fluctuations represent a fast mode. Interchange motion is possible due to the consistency between measurements and expectations. The energy source could be a pressure or density gradient in plasmaspheric plumes. When more events are accumulated so that statistical analysis becomes feasible, this type of study will be useful to understand the time evolution of plumes.
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40.
  • Matsui, H., et al. (författare)
  • Relativistic Electron Increase During Chorus Wave Activities on the 6-8 March 2016 Geomagnetic Storm
  • 2017
  • Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:11, s. 11302-11319
  • Tidskriftsartikel (refereegranskat)abstract
    • There was a geomagnetic storm on 6-8 March 2016, in which Van Allen Probes A and B separated by similar to 2.5 h measured increase of relativistic electrons with energies approximately several hundred keV to 1 MeV. Simultaneously, chorus waves were measured by both Van Allen Probes and Magnetospheric Multiscale (MMS) mission. Some of the chorus elements were rising tones, possibly due to nonlinear effects. These measurements are compared with a nonlinear theory of chorus waves incorporating the inhomogeneity ratio and the field equation. From this theory, a chorus wave profile in time and one-dimensional space is simulated. Test particle calculations are then performed in order to examine the energization rate of electrons. Some electrons are accelerated, although more electrons are decelerated. The measured time scale of the electron increase is inferred to be consistent with this nonlinear theory.
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41.
  • Matsui, H., et al. (författare)
  • Revision of empirical electric field modeling in the inner magnetosphere using Cluster data
  • 2013
  • Ingår i: Journal of Geophysical Research-Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:7, s. 4119-4134
  • Tidskriftsartikel (refereegranskat)abstract
    • Using Cluster data from the Electron Drift (EDI) and the Electric Field and Wave (EFW) instruments, we revise our empirically-based, inner-magnetospheric electric field (UNH-IMEF) model at 22.662 mV/m; K-p<1, 1K(p)<2, 2K(p)<3, 3K(p)<4, 4K(p)<5, and K(p)4(+). Patterns consist of one set of data and processing for smaller activities, and another for higher activities. As activity increases, the skewed potential contour related to the partial ring current appears on the nightside. With the revised analysis, we find that the skewed potential contours get clearer and potential contours get denser on the nightside and morningside. Since the fluctuating components are not negligible, standard deviations from the modeled values are included in the model. In this study, we perform validation of the derived model more extensively. We find experimentally that the skewed contours are located close to the last closed equipotential, consistent with previous theories. This gives physical context to our model and serves as one validation effort. As another validation effort, the derived results are compared with other models/measurements. From these comparisons, we conclude that our model has some clear advantages over the others.
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42.
  • Norgren, C., et al. (författare)
  • Electron Acceleration and Thermalization at Magnetotail Separatrices
  • 2020
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:4
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study we use the Magnetospheric Multiscale mission to investigate the electron acceleration and thermalization occurring along the magnetic reconnection separatrices in the magnetotail. We find that initially cold electron lobe populations are accelerated toward the X line forming beams with energies up to a few kiloelectron volts, corresponding to a substantial fraction of the electron thermal energy inside the exhaust. The accelerated electron populations are unstable to the formation of electrostatic waves which develop into nonlinear electrostatic solitary waves. The waves' amplitudes are large enough to interact efficiently with a large part of the electron population, including the electron beam. The wave-particle interaction gradually thermalizes the beam, transforming directed drift energy to thermal energy.
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43.
  • Norgren, Cecilia, et al. (författare)
  • Electron Reconnection in the Magnetopause Current Layer
  • 2018
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:11, s. 9222-9238
  • Tidskriftsartikel (refereegranskat)abstract
    • The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field B-G = 0.5B(in), where B-in is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out-of-plane and in-plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out-of-plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection.
  •  
44.
  • Norgren, Cecilia, et al. (författare)
  • Finite gyroradius effects in the electron outflow of asymmetric magnetic reconnection
  • 2016
  • Ingår i: Geophysical Research Letters. - : Blackwell Publishing. - 0094-8276 .- 1944-8007. ; 43:13, s. 6724-6733
  • Tidskriftsartikel (refereegranskat)abstract
    • We present observations of asymmetric magnetic reconnection showing evidence of electron demagnetization in the electron outflow. The observations were made at the magnetopause by the four Magnetospheric Multiscale (MMS) spacecraft, separated by approximate to 15km. The reconnecting current sheet has negligible guide field, and all four spacecraft likely pass close to the electron diffusion region just south of the X line. In the electron outflow near the X line, all four spacecraft observe highly structured electron distributions in a region comparable to a few electron gyroradii. The distributions consist of a core with T-vertical bar>T and a nongyrotropic crescent perpendicular to the magnetic field. The crescents are associated with finite gyroradius effects of partly demagnetized electrons. These observations clearly demonstrate the manifestation of finite gyroradius effects in an electron-scale reconnection current sheet.
  •  
45.
  • Norgren, C., et al. (författare)
  • Millisecond observations of nonlinear wave-electron interaction in electron phase space holes
  • 2022
  • Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 29:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron phase space holes (EHs) associated with electron trapping are commonly observed as bipolar electric field signatures in both space and laboratory plasma. Until recently, it has not been possible to resolve EHs in electron measurements. We report observations of EHs in the plasma sheet boundary layer, here identified as the separatrix region of magnetic reconnection in the magnetotail. The intense EHs are observed together with an electron beam moving toward the X line, showing signs of thermalization. Using the electron drift instrument onboard the satellites of the Magnetospheric Multiscale mission, we make direct millisecond measurements of the electron particle flux associated with individual electron phase space holes. The electron flux is measured at a millisecond cadence in a narrow parallel speed range within that of the trapped electrons. The flux modulations are of order unity and are direct evidence of the strong nonlinear wave-electron interaction that may effectively thermalize beams and contribute to transforming directed drift energy to thermal energy.
  •  
46.
  • Richard, Louis, et al. (författare)
  • Observations of Short-Period Ion-Scale Current Sheet Flapping
  • 2021
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Kink-like flapping motions of current sheets are commonly observed in the magnetotail. Such oscillations have periods of a few minutes down to a few seconds and they propagate toward the flanks of the plasma sheet. Here, we report a short-period (T approximate to 25 s) flapping event of a thin current sheet observed by the Magnetospheric Multiscale spacecraft in the dusk-side plasma sheet following a fast Earthward plasma flow. We characterize the flapping structure using the multi-spacecraft spatiotemporal derivative and timing methods, and we find that the wave-like structure is propagating along the average current direction with a phase velocity comparable to the ion velocity. We show that the wavelength of the oscillating current sheet scales with its thickness as expected for a drift-kink mode. The decoupling of the ion bulk motion from the electron bulk motion suggests that the current sheet is thin. We discuss the presence of the lower hybrid waves associated with gradients of density as a broadening process of the thin current sheet.
  •  
47.
  • Richard, Louis, et al. (författare)
  • Proton and Helium Ion Acceleration at Magnetotail Plasma Jets
  • 2022
  • Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate two flow bursts in a series of Earthward bursty bulk flows (BBFs) observed by the Magnetospheric Multiscale spacecraft in Earth's magnetotail at (-24, 7, 4) R-E in Geocentric Solar Magnetospheric coordinates. At the leading edges of the BBFs, we observe complex magnetic field structures. In particular, we focus on one BBF which contains large-amplitude magnetic field fluctuations on the time scale of the proton gyroperiod, and another with a large scale dipolarization. For both events, the magnetic field structures are associated with flux increases of supra-thermal ions with energies greater than or similar to 100 keV. We observe that helium ions dominate the ion flux at energies greater than or similar to 150 keV. We investigate the ion acceleration mechanism and its dependence on the mass and charge state of H+ and He2+ ions. We show that for both events, the ions with gyroradii smaller than the dawn-dusk scale of the structure are accelerated by the ion bulk flow. For ions with larger gyroradii, the acceleration is likely due to a localized spatially limited electric field for the event with a large-scale dipolarization. For the event with fluctuating magnetic field, the acceleration of ions with gyroradii comparable with the scale of the magnetic fluctuations can be explained by resonance acceleration.
  •  
48.
  • Steinvall, Konrad, et al. (författare)
  • Large Amplitude Electrostatic Proton Plasma Frequency Waves in the Magnetospheric Separatrix and Outflow Regions During Magnetic Reconnection
  • 2021
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We report Magnetospheric Multiscale observations of large amplitude, parallel, electrostatic, proton plasma frequency waves on the magnetospheric side of the reconnecting magnetopause. The waves are often found in the magnetospheric separatrix region and in the outflow near the magnetospheric ion edge. Statistical results from five months of data show that these waves are closely tied to the presence of cold (typically tens of eV) ions, found for 88% of waves near the separatrix region, and that plasma properties are consistent with ion acoustic wavegrowth. We analyze one wave event in detail, concluding that the wave is ion acoustic. We provide a simple explanation for the mechanisms leading to the development of the ion acoustic instability. These waves can be important for separatrix dynamics by heating the cold ion component and providing a mechanism to damp the kinetic Alfven waves propagating away from the reconnection site.
  •  
49.
  • Steinvall, Konrad, et al. (författare)
  • Multispacecraft Analysis of Electron Holes
  • 2019
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 46:1, s. 55-63
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron holes (EHs) are nonlinear electrostatic structures in plasmas. Most previous in situ studies of EHs have been limited to single- and two-spacecraft methods. We present statistics of EHs observed by Magnetospheric Multiscale on the magnetospheric side of the magnetopause during October 2016 when the spacecraft separation was around 6km. Each EH is observed by all four spacecraft, allowing EH properties to be determined with unprecedented accuracy. We find that the parallel length scale, l(vertical bar), scales with the Debye length. The EHs can be separated into three groups of speed and potential based on their coupling to ions. We present a method for calculating the perpendicular length scale, l. The method can be applied to a small subset of the observed EHs for which we find shapes ranging from almost spherical to more oblate. For the remaining EHs we use statistical arguments to find l/l(vertical bar)approximate to 5, implying dominance of oblate EHs. Plain Language Summary Electron holes are positively charged structures moving along the magnetic field and are frequently observed in space plasmas in relation to strong currents and electron beams. Electron holes interact with the plasma, leading to electron heating and scattering. In order to understand the effect of these electron holes, we need to accurately determine their properties, such as velocity, length scale, and potential. Most earlier studies have relied on single- or two-spacecraft methods to analyze electron holes. In this study we use the four satellites of the Magnetospheric Multiscale mission to analyze 236 electron holes with unprecedented accuracy. We find that the holes can be divided into three distinct groups with different properties. Additionally, we calculate the width of individual electron holes, finding that they are typically much wider than long, resembling pancakes.
  •  
50.
  • Tang, B-B, et al. (författare)
  • Electron Mixing and Isotropization in the Exhaust of Asymmetric Magnetic Reconnection With a Guide Field
  • 2020
  • Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:14
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate an exhaust crossing of asymmetric guide field reconnection observed by Magnetospheric Multiscale (MMS) mission at Earth's dayside magnetopause. One MMS spacecraft (MMS 4) observes multicomponent electron distributions, including two counterstreaming electron beams, while the other three MMS spacecraft, with a separation of similar to 30 km, record nearly isotropic electron distributions. As counterstreaming electrons are unstable for the electron two-stream instability, our observations suggest that the electrostatic waves generated by the fast-growing electron two-stream instability can contribute to the rapid isotropization of electron distributions in the reconnection exhaust, indicating that wave-particle interactions play an important role in electron dynamics.
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