​​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.

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.

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.

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.

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.

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.

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.

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’, k_Hall) 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.

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.

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.