ST1.11 | Turbulence in space plasmas: from injection to dissipation
EDI
Turbulence in space plasmas: from injection to dissipation
Co-organized by NP6
Convener: Olga Alexandrova | Co-conveners: Petr Hellinger, Luca Sorriso-Valvo, Julia Stawarz, Daniel Verscharen
Orals
| Mon, 24 Apr, 16:15–18:00 (CEST)
 
Room L1
Posters on site
| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)
 
Hall X4
Posters virtual
| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)
 
vHall ST/PS
Orals |
Mon, 16:15
Wed, 08:30
Wed, 08:30
Space and astrophysical plasmas are typically in a turbulent state, exhibiting strong fluctuations of various quantities over a broad range of scales. These fluctuations are non-linearly coupled and this coupling may lead to a transfer of energy (and other quantities such as cross helicity, magnetic helicity) from large to small scales and to dissipation. Turbulent processes are relevant for the heating of the solar wind and the corona, acceleration of energetic particles. Many aspects of the turbulence are not well understood, in particular, the injection and onset of the cascade, the cascade itself, the dissipation mechanisms, as well as the role of specific phenomena such as the magnetic reconnections, shock waves, expansion, and plasma instabilities and their relationship with the turbulent cascade and dissipation.
This session will address these questions through discussion of observational, theoretical, numerical, and laboratory work to understand these processes. This session is relevant to many currently operating missions (e.g., Wind, Cluster, MMS, STEREO, THEMIS, Van Allen Probes, DSCOVR) and in particular for the Solar Orbiter and the Parker Solar Probe.

Orals: Mon, 24 Apr | Room L1

Chairpersons: Olga Alexandrova, Daniel Verscharen, Julia Stawarz
16:15–16:20
16:20–16:30
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EGU23-8601
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ECS
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solicited
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On-site presentation
Ida Svenningsson, Emiliya Yordanova, Yuri V. Khotyaintsev, Mats André, and Giulia Cozzani

​​The Earth’s magnetosheath is a turbulent plasma region where the interplay between coherent structures and various plasma waves affect the particle dynamics and energy transfer. The properties of the magnetosheath are controlled by the upstream conditions. Magnetosheath plasma downstream of a quasi-parallel bow shock (the angle between the shock normal and the interplanetary magnetic field being less than 45°) tends to have stronger fluctuations while a quasi-perpendicular shock leads to a more stationary magnetosheath. These two geometries create different environments for processes such as wave generation. One example is whistler waves that can be excited by non-Maxwellian electron velocity distributions formed in local magnetic structures. Whistler waves have been observed throughout the magnetosheath. As previous statistical studies have considered the region as a whole, it is yet unexplored which magnetosheath geometry creates more favorable conditions for whistler wave generation.

In this work, we address this issue and investigate how the occurrence and properties of whistler waves depend on the magnetosheath configuration. We detect whistler waves using data from the Magnetospheric Multiscale (MMS) mission. We compare whistler wave occurrence to the shock normal angle estimated from upstream conditions, as well as local conditions which are typically different between the quasi-parallel and quasi-perpendicular geometries. The results give an indication of the conditions needed for the whistler waves to efficiently dissipate energy in the turbulent magnetosheath.

How to cite: Svenningsson, I., Yordanova, E., Khotyaintsev, Y. V., André, M., and Cozzani, G.: Whistler wave occurrence in the magnetosheath: comparing the quasi-parallel and quasi-perpendicular geometries, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8601, https://doi.org/10.5194/egusphere-egu23-8601, 2023.

16:30–16:40
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EGU23-8810
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solicited
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On-site presentation
Domenico Trotta, Francesco Pecora, Adriana Settino, Denise Perrone, David Burgess, David Lario, Heli Hietala, Timothy Horbury, Rami Vainio, Luis Preisser, William Matthaeus, Oreste Pezzi, Sergio Servidio, and Francesco Valentini

The interaction between shock and turbulence is an important pathway to energy conversion and particle acceleration in a large variety of astrophysical systems. Novel insights of such an interaction will be presented.

Using a combination of in-situ observations (using the Wind spacecraft and Magnetospheric Multiscale mission, MMS) and self-consistent kinetic simulations, the transmission of turbulent structures across the Earth’s bow shock will be discussed first. Then, the role of turbulence strength for efficient particle diffusion in phase space will be discussed using novel kinetic simulations and will be put in the context of observations of very-long lasting field aligned beams in interplanetary space. Finally, novel three-dimensional simulations of the shock turbulence interplay will be presented, with a focus on the shock front behaviour and irregular proton heating in presence of pre-existing fluctuations. In this scenario, the importance of novel multi-spacecraft missions will be discussed.

How to cite: Trotta, D., Pecora, F., Settino, A., Perrone, D., Burgess, D., Lario, D., Hietala, H., Horbury, T., Vainio, R., Preisser, L., Matthaeus, W., Pezzi, O., Servidio, S., and Valentini, F.: Transmission of turbulent structures and energetic particles dynamics in the interaction between collisionless shocks and plasma turbulence., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8810, https://doi.org/10.5194/egusphere-egu23-8810, 2023.

16:40–16:50
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EGU23-8938
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On-site presentation
Paul Cassak and M. Hasan Barbhuiya

Energy conversion between bulk kinetic and thermal energy in weakly collisional and collisionless plasma processes such as magnetic reconnection and plasma turbulence has recently been the subject of intense scrutiny. This channel of energy conversion is described by the pressure-strain interaction. In a closed system, this quantity accounts for all the net change of the thermal energy. It is common to decompose it into pressure dilatation and «Pi-D», which isolates energy conversion via compressible and incompressible physics, respectively. Here, we propose an alternative decomposition of pressure-strain interaction that instead isolates flow convergence/divergence and bulk flow shear. We furnish a simple example to illustrate how Pi-D can be counterintuitive and the new decomposition is intuitive. Moreover, for applications to magnetized plasmas, we derive the pressure-strain interaction in a magnetic field-aligned coordinate system. This results in its decomposition into eight terms, each with a different physical mechanism that changes the thermal energy. Results from particle-in-cell simulations of two-dimensional magnetic reconnection plotting the decompositions in both Cartesian and magnetic field-aligned coordinates are shown. We identify the mechanisms contributing to heating and cooling during reconnection. The results of this study are readily applicable for interpreting numerical and observational data of pressure-strain interaction in both Cartesian and field-aligned coordinates in fundamental plasma processes such as reconnection, turbulence and collisionless shocks.

How to cite: Cassak, P. and Barbhuiya, M. H.: Theoretical Developments on Energy Conversion via the Pressure-Strain Interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8938, https://doi.org/10.5194/egusphere-egu23-8938, 2023.

16:50–17:00
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EGU23-12689
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ECS
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On-site presentation
A. L. Elisabeth Werner, Emiliya Yordanova, Andrew P. Dimmock, and Ida Svenningsson

Kinetic processes control the cross-scale energy transfer between large-scale dynamics and dissipation in the solar wind. Large-scale magnetic flux ropes, also known as magnetic clouds (MCs), inside interplanetary coronal mass ejections (ICMEs) have been shown to effectively drive magnetospheric disturbances, but little is known about the turbulence properties and wave-particle interactions inside the MCs.

Here, we study the properties of the turbulence inside MCs between 0.3-1 AU observed by Solar Orbiter. We find that the spectral index in the inertial range fits Kolmogorov’s power law, but in the high-frequency regime we find a spectral bump at the beginning of a steeper power law regime. This is likely due to the presence of a significant number of whistler waves inside the MCs.

We have developed an automated search algorithm to find and record the properties of whistler waves inside MCs observed by Solar Orbiter. We find that MCs contain a significant number of whistler wave events with high magnetic field wave power (>0.5 nT2), which we do not find in the ICME sheath regions. We study these waves and attempt to determine their generation mechanism. In order to explore possible relations between the turbulence and the presence of whistler waves, we also determine the mean energy transfer rate, the magnetic field intermittency and the turbulent properties of the MCs and compare with the sheaths.  

How to cite: Werner, A. L. E., Yordanova, E., Dimmock, A. P., and Svenningsson, I.: Turbulence and whistlers in magnetic clouds observed by Solar Orbiter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12689, https://doi.org/10.5194/egusphere-egu23-12689, 2023.

17:00–17:10
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EGU23-13102
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ECS
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On-site presentation
Alina Bendt, Sandra Chapman, and Bogdan Hnat

The solar wind provides a natural laboratory for plasma turbulence at high Reynolds number. We use Solar Orbiter (SO) observations from the Magnetometer (MAG) and the Solar Wind Analyser Suite (SWA) to study extended intervals of homogeneous turbulence. Intervals which exhibit a clear scaling range of magnetohydrodynamic (MHD) turbulence, and transitions to both the ‘1/f’ range at low frequencies, and the kinetic range at frequencies where MHD is no longer valid, are selected. We ensure that all intervals are of steady solar wind flow and do not contain isolated structures such as shocks, pressure pulses and discontinuities.

Solar wind turbulence is anisotropic due to the presence of a background magnetic field. We first rotate the magnetic field into orthogonal coordinate systems with one coordinate parallel to the average direction of the magnetic field B0, a second coordinate perpendicular to both B0 and average solar wind flow direction U, and the third in the plane of both B0 and U. We then perform a Haar wavelet decomposition to obtain the timeseries of magnetic field fluctuations on multiple temporal scales. The Haar wavelet decomposition is by linearly spaced intervals in logarithmic frequency space and hence provides a precise determination of the power spectral exponents, discriminating between 5/3, 3/2 and other relevant values. It also directly estimates the Local Intermittency Measure, which characterizes localized coherent turbulent structures, and the structure functions, which quantify higher order scaling exponents.

We apply these methods to SO intervals in order to test for systematic dependencies on the properties of the turbulence with different plasma conditions and at different distances from the sun.

How to cite: Bendt, A., Chapman, S., and Hnat, B.: Wavelet determination of scaling exponents and intermittency seen by Solar Orbiter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13102, https://doi.org/10.5194/egusphere-egu23-13102, 2023.

17:10–17:20
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EGU23-13543
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ECS
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On-site presentation
Raquel Mäusle and Wolf-Christian Müller

Turbulence is of fundamental importance for many physical systems on Earth and throughout the universe. A turbulent flow can be described as the superposition of turbulent fluctuations of various length scales, which interact with each other non-linearly, leading to a transfer of energy across scales. We aim at a better understanding of the temporal and spatial properties of this energy transfer process in plasma turbulence, by studying the spatio-temporal correlation between turbulent structures in magnetohydrodynamic (MHD) turbulence.

To this end we perform three-dimensional direct numerical simulations with a pseudo-spectral method. We employ the quasi-Lagrangian reference frame, in which tracer particles are followed in the flow each carrying with it a set of probes at fixed distances across which the fluctuations are computed. This avoids the large-scale sweeping effect, which in the case of fixed-grid (Eulerian) measurements would obscure the small-scale temporal dynamics. This approach is based on previous studies in Navier-Stokes turbulence [Physics of Fluids 23.8 (2011): 085107] and has been extended to account for the magnetic field.

We investigate systems with different mean magnetic field strength. The spatio-temporal correlation functions yield insight into the nature of the cross-scale transfer of energy in terms of the direction, strength, and time scale of the transfer process. In particular, the scaling of the correlation times perpendicular and parallel to the local magnetic field, the influence of the mean magnetic field and the implications for the current understanding of the cross-scale transfer process are discussed.

How to cite: Mäusle, R. and Müller, W.-C.: Quasi-Lagrangian studies of spatio-temporal correlation in incompressible MHD turbulence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13543, https://doi.org/10.5194/egusphere-egu23-13543, 2023.

17:20–17:30
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EGU23-6971
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ECS
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On-site presentation
James Plank and Imogen Gingell

Turbulent plasmas such as the solar wind and the magnetosheath exhibit an energy cascade which is present across a broad range of scales, from the stirring scale at which energy is injected, down to the smallest scales where energy is dissipated through processes such as reconnection and wave-particle interactions. Recent observations of Earth’s bow shock reveal the presence of a disordered or turbulent transition region which exhibits some features of turbulent dissipation, such as reconnecting current sheets. Understanding the variations in the origin and character of these disordered fluctuations addresses open questions such as how disordered or turbulent fluctuations in the bow shock and magnetosheath are related, and how quickly magnetosheath turbulence arises from bow shock processes. Here, we present two case studies of bow shock crossings observed by Magnetospheric Multiscale (MMS), one quasi-perpendicular and one quasi-parallel. Using high-cadence, combined search-coil and fluxgate magnetometer data, we measure changes in correlation lengths of the magnetic field through three regions: the upstream (solar wind), shock transition region, and downstream (magnetosheath). The influence of the discontinuous shock ramp is reduced using high-pass filters with variable cut-off frequencies. We find that correlation lengths are higher on the solar wind side of the shock, reducing to around 20 ion inertial lengths in the magnetosheath for both the quasi-parallel and the quasi-perpendicular shocks. We also discuss implications of the observed evolution of the correlation length to bow shock and magnetosheath processes.

How to cite: Plank, J. and Gingell, I.: Measures of correlation length at Earth’s quasi-parallel and quasi-perpendicular bow shock, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6971, https://doi.org/10.5194/egusphere-egu23-6971, 2023.

17:30–17:40
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EGU23-13782
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ECS
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On-site presentation
Harry Lewis, Julia Stawarz, Luca Franci, Lorenzo Matteini, Kristopher Klein, and Chadi Salem

Turbulence is a complex phenomenon whereby fluctuation energy is transferred between different scale sizes as a result of nonlinear interactions. Electromagnetic turbulence is ubiquitous within space plasmas, wherein it is associated with numerous nonlinear interactions. The dynamics of the magnetic field, which are widely studied in turbulence theory, are intimately linked to the electric field, which controls the exchange of energy between the magnetic field and the particles. Magnetospheric Multiscale (MMS) provides the unique opportunity to decompose electric field dynamics into contributions from different linear and nonlinear processes. The evolution of the electric field is described by generalised Ohm’s law, which breaks down the dynamics into components arising from different physical effects. Using high-resolution multipoint measurements, we compute the MHD, Hall and Electron Pressure terms of generalised Ohm’s law for 60 turbulent magnetosheath intervals. These terms, which have varying contributions to the dynamics as a function of scale, arise as a result of different physical effects related to a range of underlying turbulent phenomena. We examine how two characteristics of the turbulent electric field spectra depend on plasma conditions: the transition scale between MHD and Hall dominance (the ‘Hall scale’, kHall) and the relative amplitude of Hall and Electron Pressure contributions. Motivated by dimensional analysis arguments which appeal to characteristics of the plasma and the turbulence that can be quantified in a number of ways by MMS, we demonstrate the necessary refinements required to reproduce measured values. The scalar isotropic kinetic Alfven wave prediction for the ratio of Electron Pressure to Hall terms as a function of plasma beta is not consistent with measurements. We observe that the MHD and Hall terms are dominated by either nonlinear or linear dynamics, depending on the interval, while the Electron Pressure term is dominated by linear components only. Our work shows how contributions to turbulent dynamics change in different plasma conditions, which may provide insight into other turbulent plasma environments.  

How to cite: Lewis, H., Stawarz, J., Franci, L., Matteini, L., Klein, K., and Salem, C.: Generalised Ohm’s Law in the Magnetosheath: How do plasma conditions impact turbulent electric fields?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13782, https://doi.org/10.5194/egusphere-egu23-13782, 2023.

17:40–17:50
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EGU23-13050
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ECS
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On-site presentation
Juska Soljento, Simon Good, Adnane Osmane, and Emilia Kilpua

Cross helicity quantifies the balance between counterpropagating Alfvénic fluctuations, which interact nonlinearly to generate turbulence in the solar wind. We have investigated how cross helicity is modified by large-scale velocity shears in the solar wind plasma. Using the linear Kelvin–Helmholtz (KH) instability threshold, we identified velocity shears at a 30-min timescale. The shears were associated with 74 interplanetary coronal mass ejection (ICME) sheaths observed by the Wind spacecraft at 1 au between 1997 and 2018. Typically weaker shears upstream of the sheaths and downstream in the ICME ejecta were also analyzed. Below the KH threshold, cross helicity was approximately invariant or weakly rising with shear amplitude. Above the KH threshold, fluctuations tended toward a balanced state with increasing shear amplitude. These findings are consistent with velocity shears being local sources of sunward fluctuations that act to reduce net imbalances in the antisunward direction, and suggest that the KH instability plays a role this process.

How to cite: Soljento, J., Good, S., Osmane, A., and Kilpua, E.: Cross helicity modified by large-scale velocity shears in the solar wind, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13050, https://doi.org/10.5194/egusphere-egu23-13050, 2023.

17:50–18:00
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EGU23-8757
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On-site presentation
Paul Loto'aniu

The magnetometer onboard the NOAA DSCOVR spacecraft samples the interplanetary magnetic field at 50 samples/second, presenting unique opportunities to study turbulence and plasma waves in the solar wind up to the instruments 25 Hz Nyquist. In this study, we present example observations by DSCOVR of turbulence and Alfven waves during periods of solar flares, coronal mass ejections, and solar energetic particle (SEP)events. We present the turbulence structures, including spectral indices at different frequencies, and discuss how it relates to coherence waves observed during cascade and dissipation. We also present wave properties, including frequency range, wave power and polarization. In addition, by comparing DSCOVR to ACE and Wind results, we discuss the dependency of solar wind parameters on spacecraft separation and the implications for studying the evolution of cascading turbulence. Finally, we explain how users can access this distinctive DSCOVR full high-resolution magnetic field dataset through the NOAA-NCEI DSCOVR portal.

How to cite: Loto'aniu, P.: DSCOVR Turbulence and Plasma Wave Observations at L1, and Correlation of Solar Wind Parameters With Spacecraft Separation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8757, https://doi.org/10.5194/egusphere-egu23-8757, 2023.

Posters on site: Wed, 26 Apr, 08:30–10:15 | Hall X4

Chairpersons: Daniel Verscharen, Julia Stawarz, Olga Alexandrova
X4.295
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EGU23-3207
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ECS
Byeongseon Park, Alexander Pitňa, Jana Šafránková, Zdeněk Němeček, Oksana Krupařová, and Vratislav Krupař

The interaction between interplanetary (IP) shocks and solar wind has been studied for the understanding of energy dissipation mechanisms and the properties of turbulence (e.g., cross helicity, residual energy, proton temperature anisotropy, magnetic compressibility, etc.) within collisionless plasmas. Compared to the study of the interaction with fast shocks, less attention has been directed to the interaction with other types of IP shocks including slow mode shocks (i.e., fast forward, fast reverse, slow forward and slow reverse). We analyze IP shocks observed by the Wind spacecraft from 1995 to 2021. Spectral indices in the ion inertial and kinetic ranges for the upstream and downstream magnetic field fluctuations are estimated by continuous wavelet transform. The changes of the plasma turbulence properties and the distributions of characteristic proton length scales are presented. We preliminarily found that spectral indices in both inertial and kinetic ranges and the distributions of characteristic proton length scales are statistically conserved across the investigated shocks. Mechanisms associated with the energy dissipation can be seen unaffected by shock. Other turbulence properties—cross helicity, residual energy and proton temperature anisotropy—evolve without a significant modification as well.

How to cite: Park, B., Pitňa, A., Šafránková, J., Němeček, Z., Krupařová, O., and Krupař, V.: The change of properties of solar wind turbulence across different types of interplanetary shocks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3207, https://doi.org/10.5194/egusphere-egu23-3207, 2023.

X4.296
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EGU23-3214
Jana Safrankova, Zdeněk Němeček, František Němec, Daniel Verscharen, Lubomír Přech, Timothy S. Horbury, and Stuart D. Bale

The contribution presents the first comprehensive statistical study of the evolution of both compressive and non-compressive magnetic field fluctuations in the inner heliosphere. Based on Parker Solar Probe and Solar Orbiter data in various distances from the Sun, we address the general trends and compare them with Wind observations near 1 AU. We analyze solar wind power spectra of magnetic field fluctuations in the inertial and kinetic ranges of frequencies. We found a systematic steepening of the spectrum in the inertial range with the spectral index of around –3/2 at closest approach to the Sun toward –5/3 at larger distances (above 0.4 AU), the spectrum of the magnetic field component perpendicular to the background field being steeper at all distances. In the kinetic range, spectral indices increase from –4.5 at closest PSP approach to –3 at ≈0.4 AU and this value remains constant toward 1 AU. We show that the radial profiles of spectral slopes, fluctuation amplitudes, spectral breaks and their mutual relation rapidly change near 0.4 AU.

How to cite: Safrankova, J., Němeček, Z., Němec, F., Verscharen, D., Přech, L., Horbury, T. S., and Bale, S. D.: Evolution of magnetic field fluctuations and their spectral properties within the heliosphere: Statistical approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3214, https://doi.org/10.5194/egusphere-egu23-3214, 2023.

X4.297
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EGU23-6538
David Pisa, Jan Soucek, Ondrej Santolik, Tomas Formanek, Milan Maksimovic, Thomas Chust, Yuri Khotyaintsev, Matthieu Kretzschmar, Christopher Owen, Philippe Louarn, and Andrei Fedorov

Ion-acoustic waves are often observed in the solar wind along the Solar Orbiter’s orbit. These electrostatic waves are generated via ion-ion or current-driven instabilities below the local proton plasma frequency. Due to the Doppler shift, they are typically observed in the frequency range between the local electron and proton plasma frequency in the spacecraft frame. Ion-acoustic waves often accompany large-scale solar wind structures and play a role in the energy dissipation in the propagating solar wind. Time Domain Sampler (TDS) receiver, a part of the Radio and Plasma Waves (RPW) instrument, is sampling wave emissions at frequencies below 200 kHz almost continuously from the beginning of the mission. Almost three years of observations allow us to perform a detailed study of ion-acoustic waves in the solar wind under variable plasma conditions. The emission tends to be observed when proton density and temperature are highly perturbed. A detailed analysis of the proton velocity distribution and wave generation using solar wind data from a Proton and Alpha particle Sensor (PAS) of the Solar Wind Analyzer (SWA) is shown.

How to cite: Pisa, D., Soucek, J., Santolik, O., Formanek, T., Maksimovic, M., Chust, T., Khotyaintsev, Y., Kretzschmar, M., Owen, C., Louarn, P., and Fedorov, A.: A detailed analysis of ion-acoustic waves observed in the solar wind by the Solar Orbiter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6538, https://doi.org/10.5194/egusphere-egu23-6538, 2023.

X4.298
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EGU23-15770
Jean-Mathieu Teissier and Wolf-Christian Müller

Magnetic helicity dynamics are important in the context of the generation of large scale magnetic structures from small scale fluctuations. Up to the present day, these dynamics have remained largely unexplored in compressible plasmas. We present new results from direct numerical simulations of isothermal magnetohydrodynamic turbulence, with Mach numbers ranging from 0.1 to 10 by employing higher-order numerics. A mechanical driving injects kinetic energy at the largest scales, while a small scale electromotive driving injects helical magnetic fluctuations. A large-scale sink of magnetic energy leads to the formation of a turbulent statistically stationary state, which is analyzed, extending the results on nonlinear cross-scale transfer presented in doi:10.1017/jfm.2021.32 and doi:10.1017/jfm.2021.496.

How to cite: Teissier, J.-M. and Müller, W.-C.: Magnetic helicity dynamics in compressible isothermal MHD turbulence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15770, https://doi.org/10.5194/egusphere-egu23-15770, 2023.

X4.299
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EGU23-16937
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ECS
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Ilyas Abushzada, Egor Yushkov, and Dmitry Sokoloff

The mechanism of stellar large-scale magnetic field formation, including the eleven-year solar cycle, is currently generally understood. In particular, its linear mode, in which the reverse effect of the magnetic field on the velocity field can be neglected. However, the non-linear reverse influence, which stabilize the growing average magnetic field, is not completely clear. The most possible reason of the nonlinear stabilization of this process is assumed the hydrodynamic helicity, but the balance of hydrodynamic and magnetic helicity and its transport along the spectrum remains to be studied. The present report is devoted to this problem. An exponential growth of magnetic energy at sufficiently high magnetic Reynolds numbers can be observed in a random short-correlated plasma flow at small-scales relative the velocity correlation length. Magnetic helicity is generated in this case together with the small-scale energy of magnetic field. And despite the fact that this phenomenon is traditionally studied by using the Kazantsev’s approach, we are trying to recreate this process of small-scale generation by a mhd shell approach, which is more convenient for the subsequent study of the balance and energy/helicity transport from small scales to large ones. To do this, in the complex shell model we add a small magnetic field to the well-established Kolmogorov spectrum and, by observing the exponential growth of magnetic energy on small scales, we compare the generation process with the magnetic small-scale Kazantsev dynamo. We select the correlation time for the velocity field and the working spectral regions to show that, in general, both approaches describe the same process with the same generation rates and scales. Thus, we show that the shell approach can be used for the future study of small-scale energy/helicity transport along the spectrum and for the problems of large-scale stellar dynamo processes stabilization. This work was supported by the BASIS Foundation grant no. 21-1-3-63-1.

How to cite: Abushzada, I., Yushkov, E., and Sokoloff, D.: Analysis of magnetic helicity generation in MHD-shell model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16937, https://doi.org/10.5194/egusphere-egu23-16937, 2023.

X4.300
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EGU23-7895
Philippe Louarn and the SWA Team + RPW and MAG

The solar wind proton distributions measured by PAS (Proton Alfa Sensor -Solar Orbiter)  are often constituted by a core and a beam. If the core is generally gaussian, the beam is asymmetric and non-gaussian with a more populated high-energy side (‘heavy tail’) in the magnetic field direction. It appears that the ‘Inverse Gaussian Distribution’ (IG), a type of hyperbolic statistical distributions, provides good fits of these skewed distributions. Then, excellent models of the whole proton distribution are obtained by superposing a gaussian (or almost gaussian distribution) for the core and an IG for the beam.  This modelling (Gaussian + Inverse Gaussian) applies to different situations: relatively slow and fast winds, single and double-bump populations, low or high level of turbulence. An interpretation is given, inspired by the ‘Normal-Inverse Gaussian’ (NIG) process, common in finance applications. Our ‘toy’ model assumes that the acceleration/heating is modelled as a drifting gaussian process in velocity space controlled (or subordinated) by an independent time-control process that follows an IG distribution. It is proposed that this control process is linked to the time of residence of the particles within accelerating structures of finite size, the relative motion between the particles and the structures being a drifting random walk (problem of the 'first passage time' of a random walk). Some applications of the model are discussed, as the estimate of the relative importance of heating and acceleration or the possible role of ambipolar fields.

How to cite: Louarn, P. and the SWA Team + RPW and MAG: The ‘Inverse-Gaussian’ SW proton populations: Do they tell something about heating/acceleration by turbulence ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7895, https://doi.org/10.5194/egusphere-egu23-7895, 2023.

X4.301
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EGU23-9803
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ECS
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Jesse Coburn, Daniel Verscharen, Christopher Owen, Timothy Horbury, Milan Maksimovic, Christopher Chen, Fan Guo, and Xiangrong Fu

Non-Maxwellian features of the coronal electron population are important for some models of solar wind acceleration processes. Remnants of these features are detectable in spacecraft observations, in particular in the form of field-aligned beams (strahl) and anti-sunward deficits in the electron distribution function. These features are shaped by expansion, collisions, and kinetic effects. Therefore, determining how these processes alter the distribution is important for our understanding of how the solar wind accelerates and evolves. The strahl and deficit contribute to the overall electron heat flux. If the heat flux crosses the threshold for instabilities, the plasma will generate waves which in turn reduce the heat flux via pitch-angle scattering of electrons out of the strahl and/or into the deficit. The work presented here examines an interval observed by Solar Orbiter during which short bandwidth whistler waves are observed by the Radio and Plasma Waves instrument. We apply a method to measure the pitch-angle gradient to high cadence pitch angle distribution (PAD) functions measured by the Electrostatic Analyser System to quantify the rate of change of heat flux from quasilinear theory. The primary part of the measurement technique is based on low-pass filtering of the PAD function with a Hermite-Laguerre transform providing a measurement of the pitch-angle gradient. We compare our quantification of the rate of change of the heat flux with other timescales and processes relevant in the solar wind. We show the potential of our technique to further our understanding of the role of wave-particle interactions in the evolution of the solar wind electrons.

How to cite: Coburn, J., Verscharen, D., Owen, C., Horbury, T., Maksimovic, M., Chen, C., Guo, F., and Fu, X.: Measurement of the rate of change of the electron heat flux due to the whistler instability with Solar Orbiter observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9803, https://doi.org/10.5194/egusphere-egu23-9803, 2023.

X4.302
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EGU23-6669
Vincent David and Sébastien Galtier

A wave turbulence theory is developed for inertial electron magnetohydrodynamics (IEMHD) in the presence of a relatively strong and uniform external magnetic field B0 = B0e. This regime is relevant for scales smaller than the electron inertial length de. We derive the kinetic equations that describe the three-wave interactions between inertial whistler or kinetic Alfvén waves. We show that for both invariants, energy and momentum, the transfer is anisotropic (axisymmetric) with a direct cascade mainly in the direction perpendicular (⊥) to B0. The exact stationary solutions (Kolmogorov–Zakharov spectra) are obtained for which we prove the locality. We also found the Kolmogorov constant CK ≃ 8.474. In the simplest case, the study reveals an energy spectrum in k−5/2k−1/2 (with k the wavenumber) and a momentum spectrum enslaved to the energy dynamics in k−3/2k−1/2. These solutions correspond to a magnetic energy spectrum ∼k−9/2, which is steeper than the EMHD prediction made for scales larger than de.

How to cite: David, V. and Galtier, S.: Wave turbulence in inertial electron magnetohydrodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6669, https://doi.org/10.5194/egusphere-egu23-6669, 2023.

X4.303
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EGU23-8164
Owen Roberts, Rumi Nakamura, Yasuhito Narita, and Zoltan Voros

We use density deduced from spacecraft potential to study the power spectral density (PSD) of fluctuations in the solar wind. Typically plasma measurements do not have high enough time resolutions to resolve ion kinetic scales. However, calibrated spacecraft potential allows much higher time resolutions to resolve the spectral break between ion inertial and kinetic ranges. Fast Survey mode data from Magnetospheric MultiScale data are used when the spacecraft were in the pristine solar wind. We find that the density spectra' morphology differs from the magnetic field fluctuations, with a flattening often occurring between inertial and kinetic ranges. We find that the spectral break of the trace magnetic field fluctuations occurs near the expected frequency for cyclotron resonance or magnetic reconnection. Meanwhile, the spectral break at the start of the ion kinetic range for density fluctuations is often at a higher frequency when compared to the magnetic field. We discuss possible interpretations for these observations. Two plausible scenarios are presented; 1. the compressive fluctuations consist of a slow wave cascade at large scales before kinetic Alfven waves become dominant at smaller scales 2. charge separation begins to occur at these scales, and the Hall electric field starts to play a role. 

How to cite: Roberts, O., Nakamura, R., Narita, Y., and Voros, Z.: The location of the spectral break in compressible fluctuations in the solar wind., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8164, https://doi.org/10.5194/egusphere-egu23-8164, 2023.

X4.304
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EGU23-11491
Chadi Salem, John Bonnell, Christopher Chaston, Kristopher Klein, Luca Franci, and Vadim Roytershteyn

Recent observational and theoretical work on solar wind turbulence and dissipation suggests that kinetic-scale fluctuations are both heating and isotropizing the solar wind during transit to 1 AU.  The nature of these fluctuations and associated heating processes are poorly understood. Whatever the dissipative process that links the fields and particles - Landau damping, cyclotron damping, stochastic heating, or energization through coherent structures - heating and acceleration of ions and electrons occurs because of electric field fluctuations. The dissipation due to the fluctuations depends intimately upon the temporal and spatial variations of those fluctuations in the plasma frame.  In order to derive that distribution in the plasma frame, one must also use magnetic field and density fluctuations, in addition to electric field fluctuations, as measured in the spacecraft frame (s/c) to help constrain the type of fluctuation and dissipation mechanisms that are at play.

We present here an analysis of electromagnetic fluctuations in the solar wind from MHD scales down to electron scales based on data from the Artemis spacecraft at 1 AU. We focus on a few time intervals of pristine solar wind, covering a reasonable range of solar wind properties (temperature ratios and anisotropies; plasma beta; and solar wind speed). We analyze magnetic, electric field, and density fluctuations from the 0.01 Hz (well in the inertial range) up to 1 kHz. We compute parameters such as the electric to magnetic field ratio, the magnetic compressibility, magnetic helicity, compressibility and other relevant quantities in order to diagnose the nature of the fluctuations at those scales between the ion and electron cyclotron frequencies, extracting information on the dominant modes composing the fluctuations. We also use the linear Vlasov-Maxwell solver PLUME to determine the various relevant modes of the plasma with parameters from the observed solar wind intervals. These results are supplemented by analysis of fully nonlinear kinetic simulations of decaying turbulence at small scales. We discuss the results and highlight  the relevant modes as well as the major differences between our results in the solar wind and results in the magnetosheath.

How to cite: Salem, C., Bonnell, J., Chaston, C., Klein, K., Franci, L., and Roytershteyn, V.: On the Nature of Ion-to-Electron Scale Field Fluctuations in the Solar Wind: Insight from Artemis Observations, Simulations and Linear Theory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11491, https://doi.org/10.5194/egusphere-egu23-11491, 2023.

X4.305
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EGU23-15845
Massimo Materassi and Giuseppe Consolini

One of the most relevant feature of turbulent fluids, included Space Plasmas, is the irregularity of the fields defining their local state (for example $\vec{B}$, $\vec{j}$ and $\vec{v}$ in the Solar Wind). In particular, time series of local quantities collected by \emph{in situ} measurements, e.g. by satellites, as well as remote sensing data, e.g. those from trans-medium communications, show scale-dependent statistical behaviour suggesting the local state fields to be better represented as \emph{fractal} or \emph{multi-fractal measures} rather than smooth functions of time and position.
In this presentation, the relationship between those measured fractal properties and the stochastic generalizations of fluid models describing the plasma is traced, suggesting a possible future development of Space Plasma turbulence theory.

How to cite: Materassi, M. and Consolini, G.: Stochasticity and fractalityin irregular space plasmas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15845, https://doi.org/10.5194/egusphere-egu23-15845, 2023.

X4.306
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EGU23-11100
Statistical observations of electron-scale structures in magnetosheath turbulence
(withdrawn)
Alexandros Chasapis, Bob Ergun, Narges Ahmadi, Steven Schwartz, Rohit Chhiber, Riddhi Bandyopadhyay, William Matthaeus, Alessandro Retino, Olivier LeContel, Barbara Giles, Daniel Gershman, Robert Strangeway, Christopher Russell, Roy Torbert, Thomas Moore, and James Burch
X4.307
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EGU23-15757
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ECS
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Xingyu Zhu, Jiansen He, Die Duan, and Rong Lin

The solar wind plasma environment in the outer heliosphere is different from the inner heliosphere where has been widely studied. An important factor influencing the turbulence evolution in the outer heliosphere is the pickup ions, primarily originated from neutral atoms from the interstellar medium. Pickup ions are not readily assimilated by the background solar wind plasma and thus provide extra free energies which can drive ion-scale instabilities. The unstable growing waves will end up taking part in the turbulent energy transport. However, how these pickup-ion-associated energies involve in turbulent cascade and influence turbulence evolution have yet to be studied. In this work, we study the solar wind turbulence evolution from 1 au to 33 au based on Voyager 2 magnetic field measurements. We study 305 time intervals listed in Pine et al. (2020). In all these time intervals, no ion-scale bumps are present in the turbulent spectra. We find that: (1) The perpendicular and trace power spectra (and ) still follow a Kolmogorov-like spectrum until 33 au while the parallel power spectrum transits from -2 to -5/3 at heliocentric distance R~10 au; (2) At periods 10 s <τ< 500 s, quasi-parallel propagation dominates in 1 au<R<7 au, with quasi-perpendicular propagation gradually emerging at R>5au. For R > 7 au, oblique propagation becomes a primary component. (3) At larger periods of τ>100 s, increases with propagation angle in 1 au<R<5 au, and in contrast decreases with propagation angle at R>5 au due to the enhanced power level at propagation angles smaller than . We suggest that such enhancement may derive from the injection of the wave energy from the pickup ion source into the background tubulent cascade , and the injected wave energy is transferred across scales withou leaving bumps in or .

How to cite: Zhu, X., He, J., Duan, D., and Lin, R.: Evolution of Turbulence Anisotropy in the Outer Heliosphere and Transport of Pickup-ion-associated Energy in Turbulence Channel : Voyager 2 Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15757, https://doi.org/10.5194/egusphere-egu23-15757, 2023.

Posters virtual: Wed, 26 Apr, 08:30–10:15 | vHall ST/PS

Chairpersons: Julia Stawarz, Olga Alexandrova, Daniel Verscharen
vSP.8
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EGU23-8814
Wiesław M. Macek and Dariusz Wójcik

We apply Fokker-Planck equation to investigate processes responsible for turbulence in space plasma. In our previous studies, we have shown that turbulence in the inertial range of hydromagnetic scales exhibits Markov properties [1,2]. We have also extended this statistical approach on much smaller scales, where kinetic theory should be applied. Namely, we have already obtained the results of the statistical analysis of magnetic field fluctuations in the Earth’s magnetosheath based on the Magnetospheric Multiscale (MMS) mission [3]. Here we compare the characteristics of turbulence behind the bow shock, inside the magnetosheath, and near the magnetopause. We check whether the second order approximation of the Fokker-Planck equation leads to kappa distribution of the probability density function provided that the first Kramers-Moyal coefficient is linear and the second term is quadratic, describing drift and diffusion correspondingly, which is a generalization of Ornstein-Uhlenbeck process. In some cases the power-law distributions are recovered. For moderate scales we have the kappa distributions described by various peaked shapes with heavy tails. In particular, for large values of the kappa parameter this is reduced to the normal Maxellian distribution. The obtained results on kinetic scales could be important for a better understanding of the physical mechanism governing turbulent systems in laboratory and space.

Keywords: Kinetic scales, Markov processes, MMS probe, Plasmas, Solar wind, Turbulence.

Acknowledgments. This work has been supported by the National Science Centre, Poland (NCN), through grant No. 2021/41/B/ST10/00823.

References

1. Strumik, M., & Macek, W. M. 2008a, Testing for Markovian character and modeling of intermittency in solar wind turbulence, Physical Review E, 78, 026414, doi=10.1103/PhysRevE.78.026414.
2. Strumik, M., & Macek, W. M. 2008b, Statistical analysis of transfer of fluctuations in solar wind turbulence, Nonlinear Processes in Geophysics, 15, 607-613, doi=10.5194/npg-15-607-2008.
3. Macek, W. M., Wójcik, D. & Burch, J. L. 2023, Magnetospheric Multiscale observations of Markov turbulence on kinetic scales, arXiv=2211.05098, Astrophysical Journal, https://doi.org/10.3847/1538-4357/aca0a0.

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How to cite: Macek, W. M. and Wójcik, D.: Comparative MMS analysis of Markov turbulence in the magnetosheath on kinetic scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8814, https://doi.org/10.5194/egusphere-egu23-8814, 2023.

vSP.9
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EGU23-7919
Subash Adhikari, Paul A. Cassak, Tulasi N. Parashar, William H. Matthaeus, and Michael A. Shay

Pressure is an important parameter in plasma turbulence. Historically, pressure fluctuations have been studied extensively via density in the nearly incompressible (NI) magnetohydrodynamic (MHD) framework1-3. However, the statistics of mechanical and total pressure in kinetic plasmas have not been explored much. In this study, we examine the statistics of mechanical and total pressure using a 2.5D particle-in-cell (PIC) simulation of plasma turbulence4. As turbulence is fully developed in the system, it is found that the magnetic and thermal pressure display a negative correlation keeping the total pressure about constant, consistent with MHD behavior. This negative correlation is observed locally in regions near the current sheets and justified by the nature of the joint probability distribution of the two5. Further, pressure spectra are calculated for magnetic, thermal and total pressure. The thermal and magnetic pressure spectra exhibit a slope of -5/3 in the inertial range, while the total pressure spectrum exhibits a slope of -7/3 in agreement with hydrodynamic scaling, influenced by the cross-spectral contribution of the individual pressures. Finally, the implications of the local structures of pressure to intermittency are discussed using probability distribution functions and scale dependent kurtosis.

1. Montgomery, D., Brown M. R., and Matthaeus W. H. "Density fluctuation spectra in magnetohydrodynamic turbulence"JGR: Space Physics A1 (1987): 282-284.

2. Matthaeus, W. H., Brown M. R., "Nearly incompressible magnetohydrodynamics at low Mach number"The Physics of Fluids 12 (1988): 3634-3644.

3. Matthaeus, W. H., et al. "Nearly incompressible magnetohydrodynamics, pseudosound, and solar wind fluctuations" JGR: Space Physics A4 (1991): 5421-5435.

4. Adhikari, S., et al. "Energy transfer in reconnection and turbulence" Physical Review E 6 (2021): 065206.

5. Adhikari S., et al. “Statistics of Total Pressure in Kinetic Plasma Turbulence" ESS Open Archive (2023).

How to cite: Adhikari, S., Cassak, P. A., Parashar, T. N., Matthaeus, W. H., and Shay, M. A.: Mechanical and Total Pressure Statistics in Vlasov-Maxwell Plasmas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7919, https://doi.org/10.5194/egusphere-egu23-7919, 2023.