Orals: Mon, 4 May, 14:00–17:55 | Room -2.15
The heating of corona and solar wind remains a fundamental but unresolved problem in space and astrophysical plasma physics. Ion cyclotron waves (ICWs) have long been proposed as a potential mechanism, energizing solar wind ions through cyclotron resonance. The wave-particle energy transfer is typically evaluated using quasilinear diffusion theory, which assumes gyrotropic ion distributions and may underestimate the actual efficiency. Therefore, high-resolution measurements of three-dimensional ion velocity distribution functions are essential to capture agyrotropic signatures arising from kinetic or nonlinear effects. Here, we report Solar Orbiter observations showing that falling-tone ICWs can efficiently energize agyrotropic protons via nonlinear cyclotron resonance. These phase-bunched ions generate resonant currents that mediate substantial energy transfer, with efficiencies up to two orders of magnitude higher than previous quasilinear estimates. These findings highlight the critical role of nonlinear wave–particle interactions in solar wind heating and acceleration, which may operate more broadly across diverse plasma environments.
How to cite: Li, J., Khotyaintsev, Y. V., Graham, D. B., and Louarn, P.: Direct Observations of Solar Wind Proton Energization via Nonlinear Cyclotron Resonance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4983, https://doi.org/10.5194/egusphere-egu26-4983, 2026.
We study Cluster Guest Investigator data when 2 satellites were at 7 km distance, that corresponds to few electron Larmor radius. We find a typical spectral shape within the kinetic range and signatures of intermittency up to electron scales. Local analysis of magnetic fluctuations at electron scales indicates presence of vortex-like coherent structures. We show that these electron scale events are embedded in coherent structures at ion and fluid scales. The results at 1 au are compared with spectral properties and coherent structures at kinetic scales observed by Parker Solar Probe at 11.4 solar radii distance from the Sun during Encounter 19.
How to cite: Alexandrova, O., Fournier, A., Hellinger, P., Maksimovic, M., Mangeney, A., and Bale, S.: Solar wind turbulence from fluid to kinetic scales: observations at 0.053 and 1 au. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3992, https://doi.org/10.5194/egusphere-egu26-3992, 2026.
Solar Orbiter observations of homogeneous turbulence at various solar wind conditions are used to estimate the power that is carried by coherent structures above a threshold across the turbulent cascade [1]. Turbulence is a potential mechanism heating the solar wind. Both wave-wave interactions and coherent structures are mechanisms that may mediate the turbulent cascade. Coherent structures have been found to be sites of dissipation.
Following the method first proposed by Bendt & Chapman (2025) [2] a threshold is determined above which fluctuations may be coherent structures. We find that the percentage of power carried by coherent structures (LIM-P) is significant, increasing with increasing frequency and maximising at ~50% just below the scale break where the inertial range transitions to the kinetic range. At distances <0.4 AU the increase of this percentage follows a roughly linear trend. Beyond 0.4 AU, there are two subranges in the inertial range. In the kinetic range, the LIM-P decreases approximately linearly with increasing frequency. We generally find more power in coherent structures in parallel than perpendicular fluctuations. Within 0.4 AU this degree of anisotropy does not vary across inertial and kinetic ranges. Beyond 0.4 AU, there is successively more power in coherent structures perpendicular than parallel fluctuations.
If coherent structures do indeed dissipate to heat the solar wind, our results, that there is significant power in coherent structures support the idea that coherent structures are important for dissipating energy of the turbulent cascade and thus solar wind heating. The trend of the LIM-P across frequencies suggests that wave-wave interactions at larger scales are systematically supplanted by coherent structures on smaller scales.
[1] Bendt & Chapman (submitted to ApJLett) Fraction of energy carried by coherent structures in the turbulent cascade in the solar wind.
[2] Bendt & Chapman (2025) Ubiquitous threshold for coherent structures in solar wind turbulence. Phys. Rev. Research doi:10.1103/PhysRevResearch.7.023176
How to cite: Bendt, A. and Chapman, S.: Evolution of power in coherent structures across scales and heliocentric distance in solar wind turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7619, https://doi.org/10.5194/egusphere-egu26-7619, 2026.
Magnetohydrodynamic (MHD) turbulence is a fundamental process in astrophysical plasmas and plays a central role in energy dissipation and particle acceleration. In this work, we use high-resolution three-dimensional MHD simulations to investigate the relationship between turbulent cascade processes and the underlying structure of the magnetic and velocity fields. We determine whether regions of enhanced energy transfer and/or dissipation correlate with regions of enhanced strain- or rotation-dominated velocity and magnetic fields.
First, we apply the filtering approach [1] to coarse-grain simulation snapshots on a given scale, obtaining spatial fields of energy transfer and dissipation. We then characterise each field as strain- or rotation-dominated using the coarse-grained tensor invariants [2,3,4], with velocity and magnetic fields treated separately. Regions of intense dissipation and energy transfer are then characterised as either strain- or rotation-dominated. This analysis is repeated across scales from the inertial range to dissipation scales to explore the relative importance of strain- and rotation-dominated features in the turbulent cascade.
The results provide insight into the phenomenology of MHD turbulence, which will be discussed in the context of recent in situ observations.
[1] M. Germano, Turbulence: the filtering approach. Journal of Fluid Mechanics. (1992) doi:10.1017/S0022112092001733
[2] V. Quattrociocchi, G. Consolini, M. F. Marcucci, and M. Materassi, On geometrical invariants of the magnetic field gradient tensor in turbulent space plasmas: Scale variability in the inertial range, Astrophys. J. (2019) doi: 10.3847/1538-4357/ab1e47
[3] B, Hnat, S. C. Chapman, C. M. Liptrott, N. W. Watkins, Solar wind magnetohydrodynamic turbulence energy transfer rate ordered by magnetic field topology Phys. Rev. Res. (2025) doi:10.1103/9wb2-r437
[4] B, Hnat, S. C. Chapman, C. M. Liptrott, N. W. Watkins, Magnetic Topology of Actively Evolving and Passively Convecting Structures in the Turbulent Solar Wind Phys. Rev. Lett. (2021) doi:10.1103/PhysRevLett.126.125101
How to cite: Liptrott, C., Chapman, S., Hnat, B., and Watkins, N.: Correlation Between Field Rotation–Strain Balance and Turbulent Cascade Processes in 3D MHD Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11490, https://doi.org/10.5194/egusphere-egu26-11490, 2026.
A natural laboratory for studying turbulence in space plasmas is the Solar Wind. The existence of intermittency in the inertial range, where the plasma dynamics can be explained within the framework of the magnetohydrodynamic model, is one of the primary characteristics of the observed turbulence. The emergence of anomalous scaling characteristics and multifractality for both magnetic and velocity field variations is the evidence of intermittency. Here, we examine the multifractal nature of the Elsasser variables demonstrating the various intermittent degrees of z± variations using data from Solar Orbiter. Additionally, by examining the joint-multi fractal spectrum, we investigate the relationship between the singularity spectra of z± fluctuations. In relation to the asymmetry of the observed singularity spectra, the significance of stochastic energy redistribution throughout the inertial cascade is also discussed.
This research is supported by the Space It Up! project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0—CUP n. I53D24000060005.
How to cite: Consolini, G., Belardinelli, D., Benella, S., and D'Amicis, R.: Intermittency and Multifractality of Elsasser Variables in Turbulent Solar Wind, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13035, https://doi.org/10.5194/egusphere-egu26-13035, 2026.
The velocity distribution functions (VDFs) of space plasma typically present non-Maxwellian shapes due to the very low level of collisisionality. The small scale gradients of the VDFs could be the key feature to explain heating and dissipation, inibiting the revesibility of the energy exchange between fields and particles once a significant level of complexity is achieved.
In this work, we investigate the solar wind protons VDFs fine features and their relation to different measures of the real space turbulent cascade. We explore different solar wind regimes and heliocentrice distances by using both Parker Solar Probe and Solar Orbiter data.
These results, suggestive of the presence of a dual velocity-real space cascade, contribute to a better understanding of turbulence in space plasmas.
How to cite: Larosa, A., Pezzi, O., Trotta, D., Ran, H., and Sorriso-Valvo, L.: Phase space cascade in the inner Heliosphere , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19459, https://doi.org/10.5194/egusphere-egu26-19459, 2026.
Turbulence plays an important role in the processes responsible for solar wind heating and acceleration by transferring energy to small scales where it is ultimately dissipated. Understanding turbulence dynamics at kinetic scales is therefore essential for determining how heating occurs in a weakly-collisional plasma. While much progress has been made at magnetohydrodynamic and ion scales, sub-electron scale turbulence remains poorly understood due to limited measurements beyond magnetic field fluctuations. However, Parker Solar Probe (PSP), equipped with its high-resolution instruments and unique near-Sun orbit, provides an excellent opportunity to study turbulence at such scales. In addition to the magnetic field (B), we obtain for the first time, the density (n) spectra (using spacecraft potential measurements) extending to scales smaller than the electron gyro-radius (ρe). At scales larger than ρe, n and B spectra exhibit similar slopes (-2.62, -2.56), indicative of Kinetic Alfvén turbulence. Below ρe, both spectra steepen, with B steepening more than n (-3.84 vs -3.28). This difference between the slopes of the two fields is consistent with turbulence becoming electrostatic in nature and the presence of an electron entropy cascade. While the n spectra has a slope close to the -10/3 prediction, the B spectra is much shallower than the expected -16/3 slope of entropy cascade. We speculate that this apparent shallowing may be due to the finite frequency resolution of the instrument and the presence of weakly damped electromagnetic fluctuations near ρe.
How to cite: Mondal, S., Chen, C., and Manzini, D.: The Nature of Turbulence at Sub-Electron Scales in the Solar Wind, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3865, https://doi.org/10.5194/egusphere-egu26-3865, 2026.
Magnetic switchbacks are large-amplitude magnetic field deflections of Alfvénic nature that are characterized by a high degree of correlation between the velocity and the magnetic fields. They are routinely detected in the inner heliosphere and are characterized by timescales that vary from hundreds of seconds up to a few hours. By means of high cadence Solar Orbiter measurements for the magnetic field vector from the fluxgate magnetometer MAG and for the reprocessed ion data sampled from the Proton and Alpha particle sensor (PAS) of the Solar Wind Analyser (SWA) suite, we have investigated their turbulent properties in terms of Alfvénicity, structure functions, and intermittency, but also how their presence affect ion kinetic features. In particular, the analysis of a case-study switchback has shown that proton and alpha particle densities increase within it, suggesting ongoing wave activity. Very interestingly, we observe a clear correlation between the magnetic deflection and alpha particle temperature, while no correlation has been found with proton temperature. This is an indication of a possible role played by switchbacks in preferentially heating heavy ions. The shapes of the proton and alphas velocity distribution functions around switchbacks will also be presented and discussed.
How to cite: Perri, S., Perrone, D., Settino, A., Chiappetta, F., D'Amicis, R., De Marco, R., Pecora, F., and Bruno, R.: Turbulence and kinetic signatures around switchbacks in the inner heliosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9415, https://doi.org/10.5194/egusphere-egu26-9415, 2026.
Coronal mass ejections (CMEs) are one of the main drivers of strong space weather disturbances. The interaction between CMEs and the Earth’s magnetic field can cause a wide range of phenomena and the magnetic configuration and orientation are key factors in determining the geo-effectiveness of this type of events. Modeling these events accurately is an ongoing challenge, and data-driven simulations are a valuable operational and research tool, widely used by the community.
Using the 3D data-driven MagnetoHydroDynamical (MHD) heliospheric solar wind and CME evolution model EUHFORIA (European Heliospheric FORecasting Information Asset), our aim is to model CME events that can impact the Earth. Forthcoming missions, developed by ASI (Italian Space Agency), aims to improve space weather forecasting capabilities, particularly for CMEs, solar energetic particles (SEPs), and other interplanetary disturbances.
In particular SEPs events are of huge importance for Space Weather risks. It is well established that particle acceleration at shocks is linked to the turbulence characterizing the environment in which particles are propagating. Consequently, understanding the role of turbulence is of fundamental importance for the propagation, acceleration and characterization of SEP events. To account for these processes, we aim to integrate the effects of both large-scale structures and turbulence in the simulations, either by using 3D EUHFORIA outputs or thorough 2.5 MHD simulation performed with MPI-ArmVAC, thereby enhancing the diagnostic capabilities of virtual spacecraft.
As a case study, we analyse the event of 3 November 2021, observed by both ACE and Solar Orbiter (SolO), which were nearly co-located in latitude and longitude, with a radial separation of ~22 million km. Comparing EUHFORIA simulations with in situ data from both spacecraft provides valuable insight into the new mission’s potential performance once operational.
This study was carried out within the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under Contract Grant Nos. 2024-5-E.0-CUP and I53D24000060005.
How to cite: Prete, G., Stefaan, P., Gatetano, Z., and Sergio, S.: From Large-Scale Structures to Turbulence: Advancing Virtual Spacecraft Diagnostics for Space Weather Forecasting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5000, https://doi.org/10.5194/egusphere-egu26-5000, 2026.
Relativistically hot plasmas are well known astrophysical sources of synchrotron emission, and the degree of linear polarization is affected by the level of turbulence in the source. Here we show, by means of a series of 3D numerical simulations, how the properties of decaying turbulence in hot plasmas depend on the magnetization of both the initial guide field and fluctuations, and how the turbulent Kolmogorov-type cascade proceeds in time. Dissipation occurs in thin, intermittent current sheets, variance anysotropy and non-Gaussian deviations appear at small scales. The computed synthetic polarization maps and degree depend on the plasma dynamics and on the angle of the line-of-sight direction with respect to the guide field. We describe how observations of these quantities may be used to infer the turbulence properties in the source.
How to cite: Del Zanna, L., Landi, S., and Bucciantini, N.: Relativistic MHD turbulence in hot plasmas and synchrotron polarization properties, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2463, https://doi.org/10.5194/egusphere-egu26-2463, 2026.
We statistically study the power spectral density (PSD) of the magnetic field turbulence in the upstream solar wind of the Martian bow shock by investigating the data from Tianwen-1 and MAVEN during November 13 and December 31 in 2021. Their spectral indices and break frequencies are automatically identified. According to the profiles of the PSDs, we find that they could be divided into three types A, B and C. Only less than a quarter of the events exhibit characteristics similar to the 1 AU PSDs (Type A). We observe the energy injection in more than one-third of the events (Type B), and find the disappearance of the dissipation range in over one third of the PSDs (Type C), which is likely due to the dissipation occurring at higher frequencies rather than proton cyclotron resonant frequencies.
We present an in-depth study of energy injection processes associated with Type-B spectra. Singular Value Decomposition analysis reveals that the gain regions are predominantly composed of compressive wave modes. Notably, a subset of these modes is identified as relatively pure, broadband ion cyclotron waves, a feature not recognized in prior statistical surveys of proton cyclotron waves. Statistical analysis of Type-B events observed by two spacecraft reveals spatial differences: events detected by MAVEN at the quasi-parallel bow shock nose are strongly influenced by the foreshock and correlate with reflected pickup ions. In contrast, concurrent events observed by Tianwen-1 on the flank show no clear connection to the foreshock or the ambient electric field direction, suggesting a potential link to upstream processes in the southern hemisphere.
The statistical study demonstrates the complicated turbulent environment of the solar wind upstream of the Martian bow shock.
How to cite: Zou, Z., Wang, Y., Wu, Z., Su, Z., and Huang, Z.: Solar Wind Turbulence Spectra and Energy Injection Upstream of Mars, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3454, https://doi.org/10.5194/egusphere-egu26-3454, 2026.
Spatiotemporal correlation of magnetic field fluctuations is investigated using the
Magnetospheric Multiscale mission in the terrestrial magnetosheath. The first observation of
the turbulence propagator emerges through analysis of more than a thousand intervals.
Results show clear features of spatial and spectral anisotropy, leading to a distinct behavior of
relaxation times in the directions parallel and perpendicular to the mean field.
The full space-time investigation of the Taylor hypothesis presents a scale-dependent
anisotropy of the magnetosheath when compared to characteristic flow propagation time and
with Eulerian estimates.
The turbulence propagator reveals that the amplitudes of the perpendicular modes decorrelate
according to sweeping or Alfvénic mechanisms. The decorrelation time of parallel modes
instead does not depend on the parallel wavenumber which could be due to resonant
interactions.
This study provides unprecedented observations into the space-time structure of turbulent
space plasmas, also giving critical constraints for theoretical and numerical models.
How to cite: Pecora, F., Matthaeus, W. H., Greco, A., Dmitruk, P., Yang, Y., Carbone, V., and Servidio, S.: Turbulence in the terrestrial magnetosheath: space-time correlation using MMS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3808, https://doi.org/10.5194/egusphere-egu26-3808, 2026.
Turbulent small‑scale dynamo action, magnetic reconnection, and kinetic instabilities in fully three‑dimensional magnetosheath turbulence must be investigated together to understand how energy is exchanged, redistributed, and dissipated in a collisionless plasma. Clarifying how these processes coexist and how they may sequence in time is essential for understanding turbulent energy transfer at sub‑ion scales. Using high‑resolution tetrahedral MMS observations in the magnetosheath, we compute a suite of diagnostics that characterize the dynamical role of velocity‑gradient structures, including field‑aligned stretching of the magnetic field, compressive motions, pressure–strain interactions, field–particle energy conversions, and pressure‑anisotropy instability measures. All quantities are derived directly from MMS time series. The measurements errors in the considered quantities are evaluated through Monte‑Carlo–based uncertainty analysis. As a working hypothesis, we examine whether regions with strong field‑aligned stretching or compression tend to coincide with magnetic‑field amplification associated with pressure‑anisotropy instabilities, conditions that may be favorable for turbulent dynamo‑like behavior. Conversely, we test whether intervals containing potentially reconnecting thin current sheets exhibit enhanced current density, elevated field particle and pressure-strain interactions and anisotropy relaxation. To explore the temporal relationships between these processes, we apply cross‑correlation analysis to the above diagnostic measures. This approach allows us to assess whether dynamo‑like amplification statistically precedes current‑sheet formation and dissipation, or whether these processes tend to overlap. Early results suggest that both ordered sequences and simultaneous occurrences are possible, reflecting the intermittent and multi‑scale nature of collisionless turbulence. The combined diagnostic and uncertainty‑quantification framework offers a possibility to evaluate the occurrence rates of magnetic‑field amplification, reconnection, and dissipation processes in collisionless space plasmas.
How to cite: Vörös, Z., Roberts, O. W., Yordanova, E., Settino, A., Upadhyay, A., Roy, S., Nakamura, R., Schmid, D., Volwerk, M., and Narita, Y.: Sub‑ion‑scale energy‑conversion pathways in magnetosheath turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7595, https://doi.org/10.5194/egusphere-egu26-7595, 2026.
Turbulence in the terrestrial magnetosheath drives rapid energy exchanges between electromagnetic fields and flows through strong intermittent compressions, shear layers, and velocity gradient structures. These concurrent and competing processes can generate temperature anisotropies and drive plasma instabilities. Yet the dynamical pathways linking velocity-gradient processes to anisotropy evolution in compressible collisionless plasmas remain poorly understood. We combine high cadence multi-point MMS measurements to quantify the pressure–strain interaction Π: ∇u (decomposed into compressible and incompressible parts), the non-ideal work J·E′, and the electron heat flux q (and ∇·q, where the signal-to-noise ratio is sufficiently large) for selected turbulent magnetosheath intervals. Physically motivated thresholds (percentile-based and background relative) identify episodes of enhanced Π: ∇u, J·E′, and heat flux activity. Then, the electron temperature anisotropy Te⊥/Te, versus parallel electron plasma βe(“Brazil”) plots are obtained from the time series under investigation, with added theoretical thresholds corresponding to whistler and firehose instabilities. In this parameter space, the trajectories of the plasma, associated with the various enhanced energy conversion and transport terms, are visualized. Case studies and ensemble statistics reveal that a dominance of different channels occurs in overlapping but non-identical regions: Π: ∇u peaks are associated with rapid anisotropy excursions and compressive structures, J·E′, with localized current and electromagnetic activity, and heat flux events with directed heat-transport toward whistler and firehose thresholds. This approach offers a practical pathway to quantify how turbulence and localized structures push plasma toward or beyond linear instability thresholds, with implications for modeling dissipation and wave generation in collisionless plasmas.
How to cite: Upadhyay, A., Vörös, Z., Roy, S., Svenningsson, I., Settino, A., Roberts, O. W., Yordanova, E., and Nakamura, R.: Multi-channel energy conversions and heat flux transport associated with pressure-anisotropy driven instabilities for electrons in magnetosheath turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7817, https://doi.org/10.5194/egusphere-egu26-7817, 2026.
In the MHD inertial range (scales larger than ion-kinetic scales) turbulent fluctuations in the solar wind are often Alfvénic in character, meaning that their magnetic and flow velocity fluctuations are proportional to each other and predominantly perpendicular to the background magnetic field. However, observations of the solar wind have shown that there is a significant difference in the energy in velocity fluctuations and normalized magnetic fluctuations. This difference, called the residual energy, should be zero for linear Alfvén waves, but is consistently observed to be negative in the solar wind, with magnetic fluctuations dominating. This work investigates the energy partition in strong three-wave interactions through an experimental campaign on the LArge Plasma Device (LAPD) in an MHD-like regime. Primary (driven) modes are launched from antennas, and secondary modes generated by the strong three-wave interaction are observed. The primary modes are shown to have no residual energy, while the secondary modes have significant residual energy - negative in the “sum” mode and positive in the “difference” mode. These results constitute the first laboratory demonstration that residual energy can indeed be generated by nonlinear mode coupling.
How to cite: Abler, M., Dorfman, S., and Chen, C. H.: First Laboratory Observations of Residual Energy Generation in Strong Alfvén Wave Interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16141, https://doi.org/10.5194/egusphere-egu26-16141, 2026.
In weakly collisional plasmas, a complete understanding of the turbulent cascade at kinetic scales remains a fundamental and elusive problem. In this regime, spatial and velocity-space fluctuations are inherently coupled, giving rise to complex patterns in which electrostatic waves continuously interact with a network of nonlinear coherent structures. This complex interplay, potentially ubiquitous across turbulent plasma environments, is thought to play a central role in controlling energy transport and dissipation. In this research, we report the first direct investigation of the nonlinear interaction between electrostatic waves and density holes at Debye and sub-Debye scales, using high-resolution Vlasov–Poisson simulations to model the dynamics of a four-dimensional (2D–2V) plasma distribution. In particular, we construct an inhomogeneous equilibrium embedded in a proton background, consisting of a periodic lattice of electron density gaps, and perturb it with nonlinear plasma oscillations in the form of turbulent electron acoustic waves. The resulting dynamics reveal a distinctive regime in which wave–hole interaction redirects the originally one-directional, wave-driven cascade into the full phase space, uncovering a previously unexplored pathway for the emergence of phase-space structures and the transfer of energy across kinetic scales.
How to cite: Celebre, G., Imbrogno, M., Servidio, S., and Valentini, F.: Phase-Space Dynamics of Electron Acoustic Turbulence in 2D-2V Inhomogeneous Plasmas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13712, https://doi.org/10.5194/egusphere-egu26-13712, 2026.
Energy transfer across scales is essential for understanding the dissipation and heating of plasma turbulence. In the energy cascade scenario, the energy transfer rate is generally quantified by the dissipation rate in the small dissipation range, along with the third-order law in the inertial range. To investigate the local properties of the energy transfer process, here we employ three main diagnostics: the locally averaged dissipation rate εr at different scales r, the local energy transfer (LET) rate, and the scale-filtered energy flux. The direct numerical simulation of three-dimensional incompressible magnetohydrodynamic (MHD) turbulence is conducted. Preliminary results include: (i) the spatial distributions of these energy transfer diagnostics show scale dependence, which also suggests that these diagnostics dominate at different scales; and (ii) even though these diagnostics could not be pointwise correlated, they exhibit similar patterns. To further quantify their correlation, we calculated the correlation functions, which show that the energy dissipation rate, the LET, and the scale-filtered energy flux have regional correlation, that is, they occur in close proximity to each other. Further analyses shall be conducted from several aspects: (i) taking into account the anisotropic effect on the energy transfer process, and (ii) extending into kinetic systems, wherein kinetic particle-in-cell (PIC) simulations shall be used, and the energy conversion channels, such as pressure-strain interaction and electromagnetic work, will be employed.
How to cite: Cheng, Z. and Yang, Y.: Statistics of Locally Averaged Energy Transfer Rate in Plasma Turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14395, https://doi.org/10.5194/egusphere-egu26-14395, 2026.
The interplay between turbulence and magnetic reconnection in collisionless plasmas is of great interest in many different space and astrophysical environments. Turbulence generates ion-scale current sheets (CSs) which reconnect, driving a turbulent cascade at sub-ion scales and thus providing a channel for energy dissipation. We present a collection of high-resolution 2D and 3D hybrid (kinetic ions, fluid electrons) simulations of plasma turbulence with different physical parameters to investigate how the macroscopic properties of the turbulent plasma background affect the dynamics and statistics of magnetic reconnection. We focus our analysis on the impact of two key parameters: the energy injection scale (i.e., the turbulence correlation length) and the amplitude of the initial fluctuations with respect to the ambient magnetic field (i.e., the turbulence strength). These two, combined, also determine the nonlinear time associated with the turbulent cascade. We first compare the similarity and differences in the properties and dynamics of the turbulence itself (shape and size of coherent structures in real space, spectral properties of the turbulent fluctuations, energy transfer rate) and then the changes in the properties and dynamics of the CSs undergoing reconnection (CS thickness and aspect ratio, reconnection rate). We discuss how the above properties rescale with respect to the two key parameters in the context of existing theories and models for turbulence and magnetic reconnection and the physical implications of our findings.
How to cite: Franci, L., Papini, E., Del Sario, D., Dhole, D., Hellinger, P., Landi, S., Verdini, A., and Matteini, L.: Effect of Turbulence Amplitude and Correlation Length on Magnetic Reconnection Dynamics in Hybrid Simulations of Collisionless Plasmas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20512, https://doi.org/10.5194/egusphere-egu26-20512, 2026.
The Pressure--Strain interaction, - (Pα • ∇ )•uα , is a fundamental diagnostic for energy conversion in collisionless space plasmas, facilitating the exchange between bulk kinetic and internal energy for both electrons (α=e) and ions (α=i) without collisional dissipation. This interaction is traditionally decomposed into two distinct physical processes: the isotropic component pθ, associated with dilatation, and the anisotropic component Pi-D, related to deviatoric deformation.
In this study, we perform a synchronized statistical analysis of these components by integrating Particle-In-Cell (PIC) simulations with in-situ observations from the Magnetospheric Multiscale (MMS) mission. By examining probability distribution functions (PDFs) and employing coarse-graining techniques, we identify contrasting statistical signatures for pθ and Pi-D. Our results indicate that pθ exhibits nearly Gaussian PDFs with kurtosis values close to a normal distribution, suggesting relatively homogeneous fluctuations across the plasma. In contrast, Pi-D displays sharply peaked, heavy-tailed PDFs, with these tails persisting even at large scales. Notably, the extreme events within the Pi-D tails are spatially correlated with coherent structures, such as current sheets and vortices.
Furthermore, scale-dependent filtering reveals that both pθ and Pi-D are highly sensitive to the analysis scale. However, a significant divergence is observed between PIC simulations and MMS data regarding their scale-dependent behaviors, highlighting potential differences between numerical modeling and high-resolution observations. We conclude that pθ serves as a distributed background channel for energy exchange, while Pi-D acts as a localized, intermittent channel. These findings clarify the statistical nature of the Pressure--Strain interaction and offer critical insights into the dissipation pathways and heating mechanisms within turbulent space environments.
How to cite: Ye, Y., Yang, Y., Wang, S., Parashar, T., Wang, Y., Wan, M., and Shi, Y.: Pressure–Strain Interaction in Collisionless Plasma Turbulence: Statistics and Scale Dependence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7850, https://doi.org/10.5194/egusphere-egu26-7850, 2026.
Posters on site: Tue, 5 May, 10:45–12:30 | Hall X4
The energy spectrum of magnetic field fluctuations in fast and alfvénic slow solar winds generally presents a spectral break at low frequencies that separates two distinct regions. In the high-frequency side of the break, the spectrum follows a power-law in frequency with exponents that vary about -3/2 and -5/3. In the lower-frequency side of the spectral break, corresponding to the largest physical scales, the spectrum is less steep and presents a power law as the inverse of the frequency. In the same range of scales, plasma fluctuations in the heliosphere are affected by deformations of the flow due to the expansion of the solar wind and velocity shear caused by wind stream interaction. We investigate the impact of these large-scale deformations of the plasma flow on turbulence properties, with our main focus being the rate at which energy of the fluctuations is transferred from large to small scales. In our study, the energy transfer rate is estimated from a Karman-Howarth-Monin (KHM) equation, a scale-dependent energy budget equation that allows to quantify the contributions of different terms to the energy transfer. We have derived a KHM equation that accounts for the combined contribution of expansion and shear in two particular cases: when the planes affected by Shear and Expansion are Aligned or Transverse (SEAT) to each other. We will present the plasma SEAT equations that model the large-scale deformation of the plasma flow, the KHM equations derived from it and preliminary numerical results from 3D single-fluid simulations that will show how both large-scale deformation of the flow intervene in the cross-scale energy transfer and affect turbulence properties.
How to cite: Montagud-Camps, V., Verdini, A., Hellinger, P., and Terradas, J.: Expansion and shear effects on cross-scale energy transfer rate: the SEAT model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14375, https://doi.org/10.5194/egusphere-egu26-14375, 2026.
The power spectral densities (PSDs) of solar wind ion moments and magnetic field turbulence in the MHD range of frequencies can be fitted by a power law with the index of -5/3 and with the power index ranging from 2 to 4 at frequencies exceeding the proton gyroscale. However, this general statement has many exceptions. As examples, (i) the density spectra exhibit a clear flattening at the high-frequency part in the MHD range but a similar effect was not reported for any other quantity, (ii) the -5/3 index is a good approximation for the magnetic field at the Earth orbit but -3/2 fits the velocity spectra better, (iii) the magnetic field spectral index evolves trough the inner heliosphere, reaching -5/3 value at 0.3 AU.
For this reason, the paper analyzes the power spectra of solar wind and magnetic field fluctuations computed in the frequency range around the break between MHD and kinetic scales. We use Spektr-R proton moments and Wind magnetic field at 1 AU, combine them with Parker Solar Probe and Solar Orbiter observations in the inner heliosphere and concentrate on the overall PSD profiles of the density, thermal speed, parallel and perpendicular components of magnetic field and velocity fluctuations and investigate statistically the role of parameters like the fluctuation amplitude, collisional age, temperature anisotropy, ion and/or electron beta and cross-helicity.
How to cite: Safrankova, J., Nemecek, Z., Nemec, F., and Durovcova, T.: Relation of the magnetic field spectral indices with plasma properties within the heliosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5056, https://doi.org/10.5194/egusphere-egu26-5056, 2026.
The difference in energy between velocity and magnetic field fluctuations in a plasma is quantified by the residual energy. In the solar wind, residual energy is typically negative at magnetohydrodynamic (MHD) inertial scales, indicating an excess of magnetic fluctuation energy that arises from the presence of magnetically dominated structures and a turbulent cascade. Recent observations have shown that fast-mode shock waves, in contrast, have a conspicuous positive signature – i.e. an excess of velocity fluctuation energy – in spectrograms of residual energy. We show how the positive residual energy of super-Alfvénic (i.e. fast-mode) MHD shocks is a natural consequence of the Rankine-Hugoniot jump conditions. The jump conditions have been used to derive an equation for the residual energy in terms of the shock angle, density compression ratio and upstream Alfvén Mach number. Values obtained from this equation agree well with the observed residual energies of 141 interplanetary shocks. The potential use of positive residual energy as a fast-mode shock identification signature in spacecraft data is considered, and the significance of these findings for understanding compressive fluctuations more generally in the solar wind is briefly discussed.
How to cite: Good, S., Palmunen, K., Chen, C., Kilpua, E., Mäkelä, T., Ruohotie, J., Sishtla, C., and Soljento, J.: Positive residual energy of magnetohydrodynamic fast-mode shocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7861, https://doi.org/10.5194/egusphere-egu26-7861, 2026.
Magnetic- and density-field fluctuations in the solar wind extend over a broad range of spatial and temporal scales. At inertial (MHD) scales, magnetic-field fluctuations are dominated by Alfvénic and/or 2D turbulence, while compressive magnetic fluctuations are associated with slow and fast MHD modes. Density fluctuations at these scales arise primarily from a mixture of entropic, slow-mode, and fast-mode contributions in the transition range near ion characteristic scales, the nature of these fluctuations changes as MHD descriptions break down and kinetic effects become important. At sub-ion scales, both magnetic-field and density fluctuations are governed by fully kinetic processes. Their coupling reflects the dominance of kinetic Alfvén wave like fluctuations, leading to enhanced compressibility and altered phase relationships between density and magnetic fields. Across all these regimes, density fluctuations—tightly linked to magnetic-field variability—play a key role in the scattering of radio waves from astrophysical sources both within and beyond the heliosphere, providing a powerful diagnostic of solar-wind turbulence across scales.
In this paper, we describe observations from two long solar wind intervals measured by the BMSW instrument onboard the Spektr-R spacecraft, which provides ion density measurements at a cadence of 32 ms. Because the Spektr-R magnetometer was not operational, we analyze magnetic-field measurements from the THEMIS-C and Wind spacecraft. The analysis of density fluctuations shows that at large (inertial) scales the fluctuations are nearly isotropic, while in the kinetic range they become strongly anisotropic. In contrast, magnetic-field fluctuations display pronounced anisotropy in both the inertial and kinetic ranges. We discuss the differing anisotropic properties of density and magnetic-field fluctuations and the complications they introduce in interpreting multi-spacecraft measurements.
How to cite: Pitna, A., Nemecek, Z., Safrankova, J., Zank, G., Kontar, E., Strauss, D. T., and Roberts, O. W.: Anisotropies of density and magnetic field fluctuations from inertial to kinetic scales in solar wind turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8023, https://doi.org/10.5194/egusphere-egu26-8023, 2026.
Interplanetary coronal mass ejections (ICMEs) and their sheath regions represent large-scale solar wind transients with distinct plasma properties compared to the solar wind. ICMEs are characterized by the presence of a large-scale flux rope, while sheaths are known for their turbulent and variable nature. At small scales, however, ICMEs, their sheaths, and the solar wind all show signs of magnetohydrodynamic turbulence. As a common property of turbulence, intermittency has been studied extensively in the solar wind and more recently also in ICMEs and their sheaths. Since intermittency manifests as non-Gaussian distributions of fluctuations, scale-dependent kurtosis is a commonly used measure for intermittency. Kurtosis is applied in different ways, with some studies using absolute or mean values of kurtosis to quantify the non-Gaussianity of the distributions at certain scales, while others use the slope of kurtosis to characterize how distributions evolve across scales. However, the interpretation of results can depend on the chosen kurtosis measure. We use data from the Wind spacecraft to study intermittency in the slow and fast solar wind, ICMEs, and ICME sheath regions. Kurtosis is computed from the local intermittency measure through wavelet analysis. Intermittency is measured both with mean values and slopes of kurtosis in the inertial range. Both measures indicate the least amount of intermittency in the fast solar wind, while some variation is observed in the case of the most intermittent plasma environment. In addition, we examine relationships between both intermittency measures and common plasma and turbulence properties.
How to cite: Ruohotie, J., Good, S., and Kilpua, E.: Comparison of intermittency in the solar wind, interplanetary coronal mass ejections and their sheath regions at 1 au, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9840, https://doi.org/10.5194/egusphere-egu26-9840, 2026.
Alfvénic fluctuations are a ubiquitous, particularly in fast streams, whereas the slow wind is typically characterized by reduced Alfvénicity and enhanced variability. However, the slow wind can display strongly Alfvénic behavior as well, with fluctuation properties comparable to those of fast streams, challenging the traditional fast–slow wind dichotomy.
In this study, we perform a comparative analysis of fast solar wind and Alfvénic slow wind during the October 2022 perihelion. In particular, we investigate the solar source and the turbulent properties of the different solar wind regimes, using plasma and magnetic field measurements from the Solar Wind Analyser (SWA) and Magnetometer (MAG) instruments onboard Solar Orbiter. We further investigate possible connections between large-scale turbulence properties and small-scale dissipation by examining the relationship between inertial-range fluctuations and magnetic-field polarization at ion scales across the spectral break. By combining in situ observations with remote-sensing data and two-step ballistic backmapping, we show that Solar Orbiter was magnetically connected to the coronal hole has a bright structure within it, indicating that the observed solar wind variability is driven by spatio-temporal changes in magnetic connectivity to coronal source. Our results show that Alfvénic slow-wind interval preserve a high degree of Alfvénicity, as evidenced by large normalized cross helicity, near kinetic–magnetic energy equipartition, low magnetic compressibility, and large-amplitude magnetic and velocity fluctuations comparable to those observed in fast Alfvénic streams, despite their lower bulk speeds and higher Coulomb collisional age. These findings pose significant challenges for solar-wind models, which must account for the persistence of strong Alfvénic turbulence in slow wind originating from nearby and evolving coronal source regions while exhibiting markedly different bulk plasma properties.
How to cite: Dhamane, O. S., D'amicis, R., Benella, S., Yardley, S., De marco, R., Bruno, R., Sorriso-Valvo, L., Telloni, D., Perrone, D., Owen, C., Louarn, P., Livi, S., Raghav, A., Kumbhar, K., Sharma, U., Kadam, S., and naik, U.: Characterization of Multiple Alfvénic Solar Wind Regimes Observed by Solar Orbiter at the October 2022 Perihelion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11085, https://doi.org/10.5194/egusphere-egu26-11085, 2026.
Collisions are nearly negligible in many space and astrophysical plasmas, allowing charged-particle velocity distribution functions (VDFs) to depart from local thermodynamic equilibrium (LTE). How collisionless plasmas relax these non-LTE distributions and convert turbulent energy into particle heating remains an open question. We investigate deviations from LTE in ion velocity distribution functions (iVDFs) within collisionless plasma turbulence using high-resolution measurements from the Magnetospheric Multiscale (MMS) mission. We find that the iVDFs' non-bi-Maxwellian features are widespread and can be significant. Their complexity increases with ion plasma beta and turbulence intensity, with pronounced high-order non-LTE features emerging during intervals of large-amplitude magnetic field fluctuations. In addition, we show that turbulence-induced magnetic curvature plays a significant role in ion scattering and contributes to the isotropization of the iVDF. These results highlight the complex interaction between turbulence and the velocity distribution of charged particles, providing new insight into the kinetic processes responsible for energy conversion in collisionless plasmas.
How to cite: Richard, L., Servidio, S., Svenningsson, I., Artemyev, A. V., Klein, K. G., Yordanova, E., Chasapis, A., Pezzi, O., and Khotyaintsev, Y. V.: Non-Maxwellianity of ion velocity distributions in the Earth's magnetosheath, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12070, https://doi.org/10.5194/egusphere-egu26-12070, 2026.
In space plasmas, turbulent relaxation processes lead to the spontaneous formation of long-lived, coherent structures. By combining solar wind observations, theoretical models, and numerical simulations, we demonstrate how the plasma locally evolves toward metastable, force-free equilibria. These persistent vortices, observed within the turbulent inertial range, act as sites for particle energization and trapping, directly influencing transport and acceleration — especially in reconnection regions between interacting magnetic islands. Recent high-resolution Magnetospheric Multiscale (MMS) measurements in the magnetosheath provide direct observational evidence of such structures, confirming their central role in mediating the turbulent cascade and dissipation. This study was carried out within the Space It Up project, funded by the Italian Space Agency (ASI) and the Ministry of University and Research (MUR), under Contract Grant Nos. 2024-5-E.0-CUP and I53D24000060005.
How to cite: Servidio, S., Pecora, F., Fortugno, E. M., Greco, A., Imbrogno, M., and Matthaeus, W. H.: Relaxation and Coherent Structures in Space Plasma Turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13144, https://doi.org/10.5194/egusphere-egu26-13144, 2026.
Energetic particles in astrophysical plasmas, both in the heliosphere and in a variety of cosmic environments, interact with turbulence that is magnetised, intermittent, and inherently multiscale. Understanding how these turbulent structures govern particle transport and acceleration is key to interpreting cosmic ray propagation, space weather phenomena, and high-energy radiation signatures. Here, I report on intial results of our ISSI Team #24-608 that brings together experts in space plasma turbulence, particle transport modeling, and spacecraft data analysis to develop the next generation of physically realistic test-particle simulations. These models incorporate turbulence features constrained by heliospheric in-situ observations from Parker Solar Probe and Solar Orbiter, as well as numerical simulations resolving coherent structures like current sheets and flux ropes across broad dynamical ranges. We investigate the role of such intermittency and structure in modifying classical diffusion coefficients and enabling anomalous transport regimes. Our approach aims to move beyond idealised turbulence assumptions, providing testable predictions for particle fluxes and anisotropies in the heliosphere and beyond. These developments offer new perspectives on energetic particle dynamics across cosmic environments, with implications for galaxy-scale feedback processes and magnetised turbulence from star-forming regions to the intergalactic medium.
How to cite: Effenberger, F., Lübke, J., Fichtner, H., and Grauer, R.: Energetic Particle Transport in Structured and Multiscale Plasma Turbulence: Bridging Observations, Theory, and Simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14406, https://doi.org/10.5194/egusphere-egu26-14406, 2026.
We verify the level of multifractality of the solar wind magnetic field fluctuations (energy density and components) measured by the Parker Solar Probe (PSP) during its first perihelion (01-09.11.2018), recently reported in literature. Two different complementary fractal approaches, namely the Rank Ordered Multifractal Analysis (ROMA, Chang and Wu 2008) and the Partition Function Multifractal Analysis (PFMA, Halsey et al. 1986) are applied, for the first time, on the same data set. ROMA considers the raw fluctuations at all scales, grouped according to their rank; PFMA provides a multifractal spectrum from a measure extracted from data and assumed to be the result of a multiplicative process. The methodology provides new insights on the multifractality close to the Sun (at 0.17-0.23 au), and complements other studies of the same dataset, at close distances from the Sun, and at solar minimum.
At 0.17 au, a cross-over is identified at a narrow range of scales centered on ~4 s (corresponding to a spatial scale of ~1400 km) separating two sub-ranges of inertial scales, with different statistical and fractal properties. The cross-over is detected by four different approaches (1) flatness behavior, (2) structure functions power law scaling, (3) change of turbulence regime across the inertial range, (4) change of the ROMA spectra over the two inertial scale-ranges. Left-skewed asymmetry of PFMA multifractal spectra further supports the complexity of the underlying dynamics dominated by large fluctuations. Conversely, the lack of right-skewed multifractal spectra at 0.17 au, as detected in the outer heliosphere, underline the different state of fluctuations near the Sun. The results have been recently accepted for publication in the Astrophysical Journal (Teodorescu et al., 2026).
Chang, T., & Wu , C.C. 2008, PhRvE, 77, 045401. doi:10.1103/PhysRevE.77.045401
Halsey, T. C., Jensen, M. H., Kadanoff, L. P. et al. 1986, PhRvA, 33, 1141–1151. doi:10.1103/PhysRevA.33.1141
Teodorescu, E., Wawrzaszek, E., Echim, M., 2026, ApJ, DOI: 10.3847/1538-4357/ae3185
How to cite: Teodorescu, E., Wawrzaszek, A., and Echim, M.: Bifractality and Cross-over Behavior Observed in Solar Wind Intermittency by Parker Solar Probe: Rank Ordered Analysis and Partition Function Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14470, https://doi.org/10.5194/egusphere-egu26-14470, 2026.
