ORCID Profile
0000-0002-5861-1643
Current Organisation
University of Southampton
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Publisher: Wiley
Date: 29-10-2020
Publisher: Wiley
Date: 02-09-2020
Publisher: American Geophysical Union (AGU)
Date: 04-2020
DOI: 10.1029/2019JA027440
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-4134
Abstract: & & Broadband waves near and below the lower-hybrid frequency have been observed at the magnetopause for a long time. In recent years NASA's multi-spacecraft mission & em& Magnetospheric Multiscale& /em& (MMS) has enabled the waves to be analysed in much greater detail.& br& Previous case studies have shown that these waves can cause plasma diffusion across the magnetopause, leading to the broadening of current layers. It has also been argued that the waves might contribute to parallel electron heating and anomalous resistivity.& & & & In this study we analyze the aforementioned waves at the magnetopause using multi-spacecraft analysis methods and data from the MMS mission. We investigate the properties of these waves on a statistical level, using several months of data. In particular, we present the relation between the waves and ambient plasma properties such as density gradients and the corresponding gradient length-scale, and to magnetic reconnection.& &
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5068
Abstract: & & High frequency electrostatic oscillations are one of the most fundamental players in energy conversion in collisionless plasmas. Whether at collisionless shocks, turbulence energy cascades or reconnection, small scale Debye length processes& are at the heart of irreversible energy exchange between particles and fields. MMS is one of the most advanced still active spacecraft, with high resolution field and particle instruments. The electric field instrument (EDP) on board of MMS is formed of 3 axial double probes positioned in a perpendicular configuration allowing for the measurement of the 3D electric field. In this study we probe the limitations of the EDP instrument in measuring Debye-scale electrostatic oscillations. In particular we show that at such small wavelengths the electric field is attenuated due to the finite probe-to-probe separation. Furthermore, we propose a method to correct for the electric field attenuation based on the single spacecraft interferometry technique which will allow us to properly determine the observed wave modes.& &
Publisher: American Geophysical Union (AGU)
Date: 11-01-2019
DOI: 10.1029/2018GL080757
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: 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: 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: 03-2022
DOI: 10.1029/2021JA030143
Abstract: When analyzing plasma waves, a key parameter to determine is the phase velocity. It enables us to, for ex le, compute wavelengths, wave potentials, and determine the energy of resonant particles. The phase velocity of a wave, observed by a single spacecraft equipped with electric field probes, can be determined using interferometry techniques. While several methods have been developed to do this, they have not been documented in detail. In this study, we use an analytical model to analyze and compare three interferometry methods applied on the probe geometry of the Magnetospheric Multiscale spacecraft. One method relies on measured probe potentials, whereas the other two use different E‐field measurements: one by reconstructing the E‐field between two probes and the spacecraft, the other by constructing four pairwise parallel E‐field components in the spacecraft spin‐plane. We find that the potential method is sensitive both to how planar the wave is, and to spacecraft potential changes due to the wave. The E‐field methods are less affected by the spacecraft potential, and while the reconstructed E‐field method is applicable in some cases, the second E‐field method is almost always preferable. We conclude that the potential based interferometry method is useful when spacecraft potential effects are negligible and the signals of the different probes are very well correlated. The method using two pairs of parallel E‐fields is practically always preferable to the reconstructed E‐field method and produces the correct velocity in the spin‐plane, but it requires knowledge of the propagation direction to provide the full velocity.
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: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-9712
Abstract: & & The recently released spacecraft potential measured by the RPW instrument onboard Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere. Selected intervals have been extracted to study and quantify the properties of turbulence. Empirical Mode Decomposition was used to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, additionally reducing issues typical of nonstationary time series. Results show the presence of a well defined inertial range with Kolmogorov scaling. However, the turbulence shows intermittency only in part of the s les, while other intervals have homogeneous scale-dependent fluctuations. These are observed predominantly during intervals of 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 provide general context and help determine the cause for the absence of intermittency.& &
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.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Konrad Steinvall.