ORCID Profile
0000-0003-1654-841X
Current Organisations
KTH Royal Institute of Technology
,
Ventspils University of Applied Sciences
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Publisher: American Geophysical Union (AGU)
Date: 20-01-2015
DOI: 10.1002/2014GL062538
Publisher: EDP Sciences
Date: 12-2021
DOI: 10.1051/0004-6361/202140943
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 S ler 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.
Publisher: American Physical Society (APS)
Date: 13-07-2017
Publisher: Copernicus GmbH
Date: 11-04-2023
DOI: 10.5194/EGUSPHERE-EGU22-4045
Abstract: & & We investigate a series of Earthward bursty bulk flows (BBFs) observed by the Magnetospheric Multiscale (MMS) spacecraft in the Earth& #8217 s magnetotail (X ~ -24 Re, Y ~ 7 Re, Z ~ 4 Re). At the leading edges of the BBFs, we observe complex magnetic field structures. In particular, we focus on one which presents a chain of small scale (~0.5 Re) dipolarizations, and another with a large scale (~3.5 Re) dipolarization. Although the two structures have different scales, both of these structures are associated with flux increases of supra-thermal ions (Ki & 100 keV). We investigate the ion acceleration mechanism and its dependence on the mass and charge state. We show that the ions with gyroradii smaller than the scale of the structure are accelerated by the ion bulk flow. We show that whereas in the small-scale structure, ions with gyroradii comparable with the scale of the structure undergo resonance acceleration, the acceleration in the larger-scale structure is more likely due to a spatially limited electric field. In both cases, we discuss the adiabaticity of the acceleration mechanism.& &
Publisher: AIP Publishing
Date: 2022
DOI: 10.1063/5.0073097
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 in idual 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.
Publisher: American Astronomical Society
Date: 31-07-2023
Publisher: American Geophysical Union (AGU)
Date: 06-07-2016
DOI: 10.1002/2016GL069205
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-7452
Abstract: & & The process of transforming the bulk kinetic energy of solar wind into the random motion of the plasma particles is still an open question. One of the proposed mechanisms for energy dissipation in such shocks is wave-particle interactions. Specifically reflected ions at the foot of the shock could interact with the solar wind plasma in an unstable way causing an increase in the temperature of the upstream plasma. Phase standing Whistler precursor waves upstream of the shock front could play a major role in enhancing energy dissipation. We analyze multiple shock crossing events encountered by the Magnetospheric Multiscale (MMS) multi-spacecraft Mission, with Alfvenic Mach numbers around 4 and a & #952 & sub& Bn& /sub& & around 80 degrees. We use these events to study the effect of such waves on energy dissipation at quasi perpendicular shocks.& Using spectral analysis and by calculating the poynting flux of the waves, we investigate the upstream shock energy transport by whistler waves, then we discuss the consequences of these results on the wave particle interaction as a mechanism for stabilizing such high Mach number shocks.& &
Publisher: American Geophysical Union (AGU)
Date: 2017
DOI: 10.1002/2016JA023572
Publisher: American Geophysical Union (AGU)
Date: 03-2016
DOI: 10.1002/2015JA021239
Publisher: American Geophysical Union (AGU)
Date: 10-2017
DOI: 10.1002/2017JA024287
Publisher: American Geophysical Union (AGU)
Date: 09-03-2021
DOI: 10.1029/2020GL090286
Abstract: We report Magnetospheric Multiscale observations of large litude, 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 d the kinetic Alfvén waves propagating away from the reconnection site.
Publisher: Wiley
Date: 29-10-2020
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-14874
Abstract: & & & span& The BIAS subsystem is a part of the Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission. It allows sending bias current to each of the three RPW antennas. & /span& By setting the appropriate bias current the antenna potential can be shifted closer to the local plasma potential. & span& This allows us to measure the floating potential of the spacecraft, as well as the electric field in the DC/LF frequency range with higher accuracy and lower noise level. Here we present the very initial results on RPW/BIAS in-flight performance based on the operations during the instrument commissioning.& /span& & &
Publisher: Wiley
Date: 02-09-2020
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-5887
Abstract: Magnetotail magnetic reconnection results in fast plasma flows referred to as jets. Reconnection jets are populated with complex non-Maxwellian ion distributions providing a source of free energy for the micro-instabilities, which contribute to the ion heating in the reconnection region. We present a statistical analysis of the ion temperature anisotropy in magnetic reconnection jets using data from the Magnetospheric Multiscale spacecraft. Compared with the quiet plasma in which the jet propagates, we often find anisotropic and non-Maxwellian ion distributions in the plasma jets. We observe magnetic field fluctuations associated with unstable ion distributions, but the wave litude is not large enough to scatter ions during the observed lifetime of the jet. Our estimate of the phase-space diffusion due to chaotic and quasi-adiabatic ion motion in the current sheet shows that the diffusion is sufficiently fast to be the main process leading to isotropization.
Publisher: Springer Science and Business Media LLC
Date: 26-05-2022
DOI: 10.1038/S41467-022-30561-8
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.
Publisher: American Geophysical Union (AGU)
Date: 07-2009
DOI: 10.1029/2008JA013197
Publisher: American Geophysical Union (AGU)
Date: 05-2022
DOI: 10.1029/2021JA029969
Abstract: Whistler waves are thought to play an essential role in the dynamics of collisionless shocks. We use the magnetospheric multiscale spacecraft to study whistler waves around the lower hybrid frequency, upstream of 11 quasi‐perpendicular supercritical shocks. We apply the 4‐spacecraft timing method to unambiguously determine the wave vector k of whistler waves. We find that the waves are oblique to the background magnetic field with a wave‐normal angle between 20° and 42°, and a wavelength of around 100 km, which is close to the ion inertial length. We also find that k is predominantly in the same plane as the magnetic field and the normal to the shock. By combining this precise knowledge of k with high‐resolution measurements of the 3D ion velocity distribution, we show that a reflected ion beam is in resonance with the waves, opening up the possibility for wave‐particle interaction between the reflected ions and the observed whistlers. The linear stability analysis of a system mimicking the observed distribution suggests that such a system can produce the observed waves.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-15746
Abstract: & & We report Solar Orbiter observations of electromagnetic waves near the proton cyclotron frequency during the first perihelion. The waves have polarization close to circular and have wave vectors closely aligned with the background magnetic field. Such waves are potentially important for heating of the solar wind as their frequency and polarization allows effective energy exchange with solar wind protons. The Radio and Plasma Waves (RPW) instrument provides a high-cadence measurement of plasma density and electric field which we use together with the magnetic field measured by MAG to characterize these waves. In particular we compute the compressibility and the phase between the density fluctuations and the parallel component of the magnetic field, and show that these have a distinct behavior for the waves compared to the Alfv& #233 nic turbulence. We compare the observations to multi-fluid plasma dispersion and identify the waves modes corresponding to the observed waves. We discuss the importance of the waves for solar wind heating.& &
Publisher: American Geophysical Union (AGU)
Date: 24-09-2015
DOI: 10.1002/2015GL065390
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-11510
Abstract: & & At Earth& #8217 s bow shock electrons can be reflected and accelerated along magnetic fields lines, which can then form electron beams and excite Langmuir and beam-mode waves. These electron beams form when the shock normal angle is close to 90 degrees. However, recent observations have shown that quasi-perpendicular shocks can be non-stationary and exhibit ripples, which can modify the local shock-normal angle and cross-shock potential. We use Magnetospheric Multiscale (MMS) data to investigate the effects of shock ripples on the accelerated electrons observed in the electron foreshock. We compare the results with test-particle simulations to determine the effect of shock ripples on electron acceleration. We discuss the implications of these results for the generation of plasma frequency waves and radio emission in the electron foreshock region.& span& & & /span& & &
Publisher: American Geophysical Union (AGU)
Date: 09-2017
DOI: 10.1002/2017JA024553
Publisher: Wiley
Date: 28-02-2021
Publisher: American Geophysical Union (AGU)
Date: 04-2016
DOI: 10.1002/2015JA021527
Publisher: American Geophysical Union (AGU)
Date: 28-08-2018
DOI: 10.1029/2018GL078660
Publisher: American Geophysical Union (AGU)
Date: 11-06-2016
DOI: 10.1002/2016GL069192
Publisher: American Physical Society (APS)
Date: 13-09-2023
Publisher: Wiley
Date: 02-09-2020
Publisher: American Geophysical Union (AGU)
Date: 11-08-2021
DOI: 10.1029/2021GL093164
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‐ litude nonlinear upper‐hybrid (UH) waves on both sides of the neutral line, and the wave litudes 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.
Publisher: American Geophysical Union (AGU)
Date: 20-06-2016
DOI: 10.1002/2016GL069191
Publisher: American Astronomical Society
Date: 30-05-2018
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-11451
Abstract: & & & span& We analyze in detail a reconnection site observed by the Magnetospheric Multiscale (MMS) mission in the magnetotail.& /span& & span& The interval around the X-line is identified based on the ion jet reversal, Hall electric fields and other reconnection signatures. At the reconnection site strong electric fields with litudes above 100mV/m are observed. In addition, the region shows strong turbulent variations on ion scales, including magnetic island-like structures. We discuss the cause of strong electric fields, their relation to ion scale structures and associated particle acceleration in this region. & /span& & span& Of particular interest is the relation of the reconnection site to the generation of kinetic Alfven waves.& /span& & &
Publisher: American Geophysical Union (AGU)
Date: 04-2020
DOI: 10.1029/2019JA027440
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-15860
Abstract: & & Thin current sheets are routinely observed in the solar wind. Here we report observations of thin current sheets and the associated plasma waves using the Solar Orbiter spacecraft. The Radio and Plasma Waves (RPW) instrument provides high-resolution measurements of the electric field, number density perturbations, and magnetic field fluctuations, which we use to identify and characterise the observed waves, while the magnetic field provided by the MAG instrument is used to characterise the current sheets. We discuss the role of current sheets in the generation of the observed waves and the effects of the waves on the current sheets.& span& & & /span& & &
Publisher: American Geophysical Union (AGU)
Date: 18-05-2016
DOI: 10.1002/2016GL068613
Publisher: American Geophysical Union (AGU)
Date: 05-07-2016
DOI: 10.1002/2016GL069665
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-14805
Abstract: & & Energy dissipation at collisionless shocks is still an open question. Wave particle interactions are believed to be at the heart of it, but the exact details are still to be figured out. One type of waves that is known to be an efficient dissipator of solar wind kinetic energy are electrostatic waves in the shock r , such as ion acoustic waves with frequency around the ion plasma frequency or Bernstein waves with frequency around the electron cyclotron frequency and its harmonics. The electric field of such waves is typically larger than 100 mV/m, large enough to disturb particle dynamics. In this study we use the magnetospheric multiscale (MMS) spacecraft, to investigate the source and evolution of electrostatic waves in the shock r of quasi-perpendicular super-critical shocks, and study their effect on solar wind thermalization.& &
Publisher: American Geophysical Union (AGU)
Date: 16-07-2016
DOI: 10.1002/2016GL069188
Publisher: American Geophysical Union (AGU)
Date: 15-01-2016
DOI: 10.1002/2015GL067187
Publisher: American Geophysical Union (AGU)
Date: 06-06-2016
DOI: 10.1002/2016GL069064
Publisher: American Geophysical Union (AGU)
Date: 10-2021
DOI: 10.1029/2021JA029260
Abstract: Plasmas in Earth's outer magnetosphere, magnetosheath, and solar wind are essentially collisionless. This means particle distributions are not typically in thermodynamic equilibrium and deviate significantly from Maxwellian distributions. The deviations of these distributions can be further enhanced by plasma processes, such as shocks, turbulence, and magnetic reconnection. Such distributions can be unstable to a wide variety of kinetic plasma instabilities, which in turn modify the electron distributions. In this paper, the deviation of the observed electron distributions from a bi‐Maxwellian distribution function is calculated and quantified using data from the Magnetospheric Multiscale spacecraft. A statistical study from tens of millions of electron distributions shows that the primary source of the observed non‐Maxwellianity is electron distributions consisting of distinct hot and cold components in Earth's low‐density magnetosphere. This results in large non‐Maxwellianities at low densities. However, after performing a statistical study we find regions where large non‐Maxwellianities are observed for a given density. Highly non‐Maxwellian distributions are routinely found at Earth's bowshock, in Earth's outer magnetosphere and in the electron diffusion regions of magnetic reconnection. Enhanced non‐Maxwellianities are observed in the turbulent magnetosheath, but are intermittent and are typically not correlated with local processes. The causes of enhanced non‐Maxwellianities are investigated.
Publisher: American Geophysical Union (AGU)
Date: 12-2020
DOI: 10.1029/2020JA028592
Abstract: We report the detection of large‐ litude, quasi‐harmonic density fluctuations with associated magnetic field oscillations in the region surrounding the diamagnetic cavity of comet 67P. Typical frequencies are ∼ 0.1 Hz, corresponding to ∼ 10 times the water and times the proton gyro‐frequencies, respectively. Magnetic field oscillations are not always clearly observed in association with these density fluctuations, but when they are, they consistently have wave vectors perpendicular to the background magnetic field, with the principal axis of polarization close to field‐aligned and with a ∼ 90° phase shift with respect to the density fluctuations. The fluctuations are observed in association with asymmetric plasma density and magnetic field enhancements previously found in the region surrounding the diamagnetic cavity, occurring predominantly on their descending slopes. This is a new type of waves not previously observed at comets. They are likely ion Bernstein waves, and we propose that they are excited by unstable ring, ring‐beam, or spherical shell distributions of cometary ions just outside the cavity boundary. These waves may play an important role in redistributing energy between different particle populations and reshape the plasma environment of the comet.
Publisher: Wiley
Date: 04-2018
DOI: 10.1002/2017JA025034
Publisher: American Geophysical Union (AGU)
Date: 23-11-2018
DOI: 10.1029/2018GL080826
Publisher: American Geophysical Union (AGU)
Date: 09-2019
DOI: 10.1029/2019GL084137
Publisher: American Geophysical Union (AGU)
Date: 11-2019
DOI: 10.1029/2019JA027155
Abstract: Waves around the lower hybrid frequency are frequently observed at Earth's magnetopause and readily reach very large litudes. Determining the properties of lower hybrid waves is crucial because they are thought to contribute to electron and ion heating, cross‐field particle diffusion, anomalous resistivity, and energy transfer between electrons and ions. All these processes could play an important role in magnetic reconnection at the magnetopause and the evolution of the boundary layer. In this paper, the properties of lower hybrid waves at Earth's magnetopause are investigated using the Magnetospheric Multiscale mission. For the first time, the properties of the waves are investigated using fields and direct particle measurements. The highest‐resolution electron moments resolve the velocity and density fluctuations of lower hybrid waves, confirming that electrons remain approximately frozen in at lower hybrid wave frequencies. Using fields and particle moments, the dispersion relation is constructed and the wave‐normal angle is estimated to be close to 90° to the background magnetic field. The waves are shown to have a finite parallel wave vector, suggesting that they can interact with parallel propagating electrons. The observed wave properties are shown to agree with theoretical predictions, the previously used single‐spacecraft method, and four‐spacecraft timing analyses. These results show that single‐spacecraft methods can accurately determine lower hybrid wave properties.
Publisher: American Geophysical Union (AGU)
Date: 11-2018
DOI: 10.1029/2018JA025676
Publisher: American Geophysical Union (AGU)
Date: 09-2018
DOI: 10.1029/2018JA025874
Publisher: American Physical Society (APS)
Date: 28-05-2014
Publisher: American Geophysical Union (AGU)
Date: 11-01-2019
DOI: 10.1029/2018GL080757
Publisher: American Geophysical Union (AGU)
Date: 13-07-2016
DOI: 10.1002/2016GL069877
Publisher: American Geophysical Union (AGU)
Date: 11-2017
DOI: 10.1002/2017JA024535
Abstract: In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi‐parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid‐scale and kinetic‐scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent‐like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-4295
Abstract: & & The Magnetospheric Multiscale spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large- litude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The litude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. Our analysis shows that the EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.& &
Publisher: American Geophysical Union (AGU)
Date: 10-2016
DOI: 10.1002/2016JA023146
Abstract: Localized kinetic‐scale regions of strong current are believed to play an important role in plasma thermalization and particle acceleration in turbulent plasmas. We present a detailed study of a strong localized current, 4900 nA m −2 , located at a fast plasma jet observed in the magnetosheath downstream of a quasi‐parallel shock. The thickness of the current region is ∼3 ion inertial lengths and forms at a boundary separating magnetosheath‐like and solar wind‐like plasmas. On ion scales the current region has the shape of a sheet with a significant average normal magnetic field component but shows strong variations on smaller scales. The dynamic pressure within the magnetosheath jet is over 3 times the solar wind dynamic pressure. We suggest that the current sheet is forming due to high velocity shears associated with the jet. Inside the current sheet we observe local electron acceleration, producing electron beams, along the magnetic field. However, there is no clear sign of ongoing reconnection. At higher energies, above the beam energy, we observe a loss cone consistent with part of the hot magnetosheath‐like electrons escaping into the colder solar wind‐like plasma. This suggests that the acceleration process within the current sheet is similar to the one that occurs at shocks, where electron beams and loss cones are also observed. Therefore, electron beams observed in the magnetosheath do not have to originate from the bow shock but can also be generated locally inside the magnetosheath.
Publisher: EDP Sciences
Date: 12-2021
DOI: 10.1051/0004-6361/202140936
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 (∼0.5 AU 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° 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 different 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 × 10 6 λ 10 6 m. We conclude that it is most likely that both the left- and right-handed waves correspond to the low-wavenumber part (close to the cut-off at Ω c He + + ) of the proton-band electromagnetic ion cyclotron (left-handed wave in the plasma frame confined to the frequency range Ω c He + + ω Ω 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.
Publisher: American Geophysical Union (AGU)
Date: 08-2022
DOI: 10.1029/2022JA030430
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‐ litude 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 ≳100 keV. We observe that helium ions dominate the ion flux at energies ≳150 keV. We investigate the ion acceleration mechanism and its dependence on the mass and charge state of H + and He 2+ 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.
No related grants have been discovered for Andris Vaivads.