Turbulence is three-dimensional, multiscale disorder. Characterizing turbulence requires determining how energy is injected into, transported through, and removed from these systems. One can study the three-dimensional structure by using measurements from at least four spatial points combined with appropriate analysis approaches to estimate spatial gradients and distributions of power at a given scale. Such techniques have been applied to data from spacecraft missions such as MMS and Cluster, but are limited to a single scale associated with the average inter-spacecraft distance. Given that future selected and proposed spacecraft missions, including HelioSwarm and Plasma Observatory, will have many more than four measurement points, with separations between the spacecraft spanning different characteristic spatial scale lengths, we consider the extension of previously implemented analysis techniques to these multipoint, multiscale configurations. In particular, we consider the propagation of measurement error through the wave telescope technique as a function of the number of measurements points and configuration to demonstrate the impact on accurate resolution of the underlying wavevectors. We also explore the optimal selection of subsets of measurement points to more accurately measure the properties of plane waves and wave packets with wavevectors spanning the spatial scales encompassed by a representative multispacecraft observatory.

How to cite: Klein, K. and Broeren, T.: Analysis Techniques for Future Multipoint, Multiscale Observatories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10703, https://doi.org/10.5194/egusphere-egu24-10703, 2024.

The HelioSwarm mission was selected as a MIDEX mission by NASA in February 2022 for launch in 2029 with a nominal duration of 15 months. Its main objectives are to reveal the 3D spatial structure and dynamics of turbulence in a weakly collisional plasma and to investigate the mutual impact of turbulence near boundaries (e. g., Earth’s bow shock and magnetopause) and large-scale structures evolving in the solar wind (e. g., coronal mass ejection, corotating interaction region). The HelioSwarm mission will also contribute to the space weather science and to a better understanding of the Sun-Earth relationship. It consists of a platform (Hub) and eight smaller satellites (nodes) evolving along an elliptical orbit with an apogee ~ 60 and a perigee ~15 Earth radii. These 9 satellites, three-axis stabilised, will provide 36 pair combinations and 126 tetrahedral configurations covering the scales from 50~km (subion scale) to 3000 km (MHD scale). It will be the first mission able to investigate the physical processes related to cross-scale couplings between ion and MHD scales by measuring, simultaneously at these two scales, the magnetic field, ion density and velocity variations. Thus each satellite is equipped with the same instrument suite. A fluxgate magnetometer (MAG from Imperial College, UK) and a search-coil magnetometer (SCM) provide the 3D measurements of the magnetic field fluctuations whereas a Faraday cup (FC, SAO, USA) performs the ion density and velocity measurements. In addition, the ion distribution function is measured at a single point onboard the Hub by the iESA instrument, allowing to investigate the ion heating in particular. The SCM for HelioSwarm provided by LPP and LPC2E is strongly inherited of the SCM designed for the ESA JUICE mission. It will be mounted at the tip of a 3m boom and will cover the frequency range associated with the ion and subion scales in the near-Earth environment [0.1-16Hz] with the following sensitivities [15pT/√Hz at 1 Hz and 1.5 pT/√Hz at 10 Hz]. The iESA, developped by IRAP and LAB, is inherited from the PAS instrument operating on the ESA Solar Orbiter mission. It will provide the ion distribution function at high time and angular resolutions, respectively 0.150 s and 3°. Furthermore the energy range will be ~200 eV to 20 keV with 8% energy resolution. Status of the development of SCM and iESA prototypes will be presented.

How to cite: Le Contel, O., Lavraud, B., Retino, A., Kretzschmar, M., Génot, V., Alexandrova, O., Mansour, M., Amoros, C., Jannet, G., Baruah, R., Mehrez, F., Camus, T., Alison, D., Grigoriev, A., Revillet, C., Studniarek, M., Mirioni, L., Agrapart, C., Sou, G., and Geyskens, N. and the HelioSwarm team: The French contribution for the NASA HelioSwarm mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9272, https://doi.org/10.5194/egusphere-egu24-9272, 2024.

The paper analyzes the power spectra of solar wind velocity and magnetic field fluctuations that are computed in the frequency range around the break between inertial and kinetic scales. The study uses measurements of the Bright Monitor of the Solar Wind (BMSW) on board Spektr-R with a time resolution of 32 ms complemented with 10 Hz magnetic field observations from Wind propagated to the Spektr-R location and compare them with observations of Solar Orbiter and Parker Solar Probe closer to the Sun. We concentrate on the ion kinetic scale and investigate statistically the role of parameters like the fluctuation amplitudes of parallel and perpendicular magnetic field components, collisional age, temperature anisotropy or ion and electron beta. Our discussion encompasses the interplay of magnetic field and plasma fluctuations that characterize this dynamic environment and reveals that although the ion beta controls a position of the spectral break between the inertial and kinetic ranges, other mentioned parameters determine the steepness of the kinetic range spectrum of both quantities. We are showing that these statistical results are in line with theoretical considerations.

How to cite: Safrankova, J., Nemecek, Z., Pitna, A., Nemec, F., and Franci, L.: Magnetic field and ion velocity spectra in the solar wind from inertial to kinetic scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4307, https://doi.org/10.5194/egusphere-egu24-4307, 2024.

We present wave and turbulence observations by the DSCOVR spacecraft during solar flare and CME events. Over 9-day period, the spectral indices within the magnetic field power spectral density (PSD) in the RTN and mean-field-aligned (MFA) coordinates do not agree. In the inertial range the transverse PSD follows a Kraichnan–Iroshinikov -3/2 index when in MFA coordinates, while in the RTN frame the same PSD is more complex showing Kolmogorov -5/3 index at lower frequencies followed by a shallow index close to -1 at the inertial subrange before steepening to -2 close to the He+ cyclotron frequency. We show that the differences are due to the changing interplanetary magnetic field (IMF) direction relative to the solar wind velocity within the CME periods. We present evidence of wave-wave modulation and suggest that lower frequency waves in the solar wind can modulate the growth rates/propagation of ion cyclotron waves providing a method to transfer energy in the solar wind to smaller scales. Furthermore, we suggest that the Kraichnan–Iroshinikov -3/2 index in the inertial range can be explained by combining containment due to wave generation/propagation and stochastic Brownian motion in the solar wind. When these two phenomena are equal, they combine to create a -3/2 index.

How to cite: Loto'aniu, P. and Krista, L.: Spectral Indices and Evidence of Wave-Wave Modulation in Observations of the Interplanetary Magnetic Field, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7101, https://doi.org/10.5194/egusphere-egu24-7101, 2024.

The existing Alfven Wave Turbulence Based Solar Atmosphere Model (AWSoM) as used in the SWMF framework of the University of Michigan to simulate the Solar Corona and Inner Heliosphere (i.e. to 1 AU heliocentric distance) meets an ideological problem while compared with the equations for turbulence usually employed in modeling the outer heliosphere (i.e. beyond 1 AU). While for the turbulence in the outer heliosphere the energy difference (the difference between the averaged kinetic and magnetic energy densities) is used as one of the Reynolds-averaged quantity describing the local state of turbulence, the present AWSoM model lacks the energy difference at all. 

Besides an evident inconsistency between the models of turbulence, employing the different sets of variables below and beyond 1 AU, to have a full description of turbulence is important by two reasons, both relating to the charged particle transport producing the radiation hazards in space. First, for simulation both solar energetic particle and galactic cosmic rays at 1 AU a computational domain should extend at least to 2-3 AU. Second, even if below 1 AU the energy difference effect on turbulence might be negligible and not necessary to be included into the turbulence model, it is still needed to calculate transport coefficients for the high energy charged particles in the turbulent magnetic field. To evaluate it from the averaged quantities characterizing the turbulence, both the total energy density and the said energy difference are needed. 

In the presented research, an extra equation for the energy difference in introduced and solved in such way that at small heliocentric distances the turbulence model reduces to that used in the AWSoM with no loss in generality. On the other hand at larger heliocentric distances it becomes very close (if not identical) to the typical outer heliosphere model. In addition to averaged energetic characteristics of turbulence we evaluate the correlation spatial scales for directions parallel and perpendicular to the averaged interplanetary magnetic field was well as the transport coefficients for high-energy charged particles

How to cite: Sokolov, I., Usmanov, A., van der Holst, B., and Gombosi, T.: Unified Alfven Wave Turbulence Based Model for Energy and Particle Transport in Solar Corona and Heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20578, https://doi.org/10.5194/egusphere-egu24-20578, 2024.

Turbulent magnetic dynamo models were created about fifty years ago to describe the growth of the average magnetic energy in random convective plasma flows. A typical feature of such models is the generation threshold, when the exponential growth of magnetic energy begins only at sufficiently large magnetic Reynolds numbers Rm. In particular, one of the first models, proposed in the 70th by Kazantsev and Kraichnan, predicts a generation threshold in the region of Reynolds numbers of the order of 100. This threshold is difficult to achieve even for modern laboratory experiments, and therefore many studies in recent years have been devoted to clarifying this critical value. However, there is a sufficient disadvantage of usually used turbulent dynamo model – the assumption about delta-correlated in time random velocity field. This nonphysical assumption makes one unconfident in the correctness of the estimate of the dynamo threshold. In this work, using shell MHD models, we are trying to find out how accurate Kazantsev’s estimate of the generation threshold is, and how this threshold depends on the flow velocity, diffusion coefficients, and hydrodynamic helicity. This work was supported by the BASIS Foundation grant no. 21-1-3-63-1.

How to cite: Abushzada, I. and Yushkov, E.: A turbulent dynamo threshold in the shell-model approximation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-260, https://doi.org/10.5194/egusphere-egu24-260, 2024.

We study intermittent coherent structures in solar wind magnetic turbulence from MHD to kinetic plasma scales using  Parker Solar Probe data during its first perihelion (at 0.17 au). These structures are energetic events localized in time and covering wide range of scales. We detect them using Morlet wavelets. For the first time, we apply a multi-scale analyses in physical space to study these structures. At large MHD scales, we find (i) current sheets including switchback boundaries and (ii) Alfvén vortices. Within these large scale events, there are  embedded structures at smaller scales: typically  Alfvén vortices at ion scales and a compressible vortices at sub-ion scales. To quantify the relative importance of different type of structures, we do a statistical comparison of the observed structures with the expectations of models of the current sheets and vortices. This comparison is based on amplitude anisotropy of magnetic fluctuations within the structures. The results show the dominance of Alfvén vortices at all scales in contrast to the widespread view of dominance of current sheets. The number of coherent structures grows from the MHD to the sub-ion scales. For one MHD scale structure there are ∼10 ion scale structures and ∼50  sub-ion scale structures. In general, there are multiple structures of ion and sub-ion scales embedded within one MHD structure. There are also examples of non-embedded structures at ion and sub-ion scales.

How to cite: Alexandrova, O., Vinogradov, A., Demoulin, P., Artemyev, A., Maksimovic, M., Mangeney, A., and Bale, S.: Embedded coherent structures from MHD to sub-ion scales in turbulent solar wind: PSP observations at 0.17 au, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17557, https://doi.org/10.5194/egusphere-egu24-17557, 2024.

The origin and evolution of non-equilibrium characteristics of electron velocity distribution functions (eVDFs) in the solar wind are still not well understood. They are key in understanding heat conduction and energy transport in weakly collisional plasma, as well as in the scenario at the origin of the solar wind. Due to low collision rates in the solar wind, the electron populations develop temperature anisotropies and velocity drifts in the proton frame, as well as suprathermal tails and heat fluxes along the local magnetic field direction. These non-thermal characteristics are highly variable, and the processes that control them remain an open question.  

We present here a recent work on enhanced measurements of solar wind eVDFs from Wind at 1AU. This work is based on a sophisticated algorithm that calibrates eVDFs with plasma Quasi Thermal Noise data in order to accurately and systematically characterize the non-thermal properties of the eVDFs, as well as those of their Core, Halo and Strahl components.  Indeed, the core, halo and strahl populations are fitted to determine their densities, temperatures and temperature anisotropies as well as their respective drift velocities with respect of the ion velocity (or solar wind speed).  The density, temperature and temperature anisotropy, as well as the parallel heat flux of the total eVDFs are also computed. 

We use a 4-year-long dataset composed of all these parameters at solar minimum to enable statistically significant analyses of solar wind electron properties. We estimate collisional proxies such as collisional age and Knudsen number, and discuss usually neglected effects. In addition to the total electron heat flux, we also compute the heat flux contributions from the core, halo and strahl and discuss the interplay between these three components.  We finally show estimates of the so-called Thermal Force, a drag or Coulomb friction between ions and the electron components that arises naturally from the non-thermal character of the eVDFs, even in the absence of current. This TF enhances the parallel electric field and plays an important, but usually neglected, role in two fluid energy transfers between electrons and ions. It is parallel to the heat flux that causes it, however its role in understanding the observed heat flux remains to be explored.  This statistically-significant work allows a local, quantitative measure of Coulomb coupling that maybe important with possibly other microphysical processes to locally control non-thermal properties.

How to cite: Salem, C., Pulupa, M., Verscharen, D., and Yoon, P.: New Insights on Solar Wind Electrons at 1 AU: Collisionality, Heat Flux, and Thermal Force, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13061, https://doi.org/10.5194/egusphere-egu24-13061, 2024.

The Voyager 1 and 2 are only the two spacecraft that have arrived and passed through the heliospheric boundaries. Based on the plasma data from Voyager 2 spacecraft, the electron quasi-thermal noise (QTN) is investigated by using of the electron population model consisting of a core with Maxwellian distribution and a halo with kappa distribution. The power spectra of the electron QTN is calculated at different heliocentric distances from 1 AU to 110 AU. The parametric dependence of the QTN power spectra and the effective Debye length on the model parameters, such as the density ratio and temperature ratio of the halo to the core, kappa index and the antenna length, are discussed further. The results show that the electron QTN spectrum consists of a plateau in the low frequency band f < fpt, a prominent peak at the plasma frequency fpt, and a rapid decreasing part in the high frequency band f > fpt. The QTN plateau level basically falls down outwards until the termination shock crossing at about 84 AU, after which the plateau rebounds a little near the heliopause. Although the model parameters can be very variable, the QTN plateau level does not present more than the double change in a fairly wide range of the model parameters. The presented results can be useful for future deep-space explorations in the heliosphere and can provide valuable references for the design of onboard detectors.

How to cite: Li, Y.-L., Chen, L., and Wu, D.-J.: Radial Distribution of Electron Quasi-thermal Noise in the Outer Heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17726, https://doi.org/10.5194/egusphere-egu24-17726, 2024.