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.

Compressible fluctuations represent a key element of turbulence in astrophysical plasmas, where the compression and expansion of turbulent flows play a critical role in regulating energy transfer and dissipation. In this work, we examine how local streamline topology and energy cascade rate self-organize in plasma turbulence at a fixed scale. Using a fully compressible Hall-magnetohydrodynamic simulation, we quantify the subgrid-scale energy transfer and analyze its relationship to streamline structures by means of gradient-tensor geometric invariants of the velocity field. Our results highlight how streamline topology is crucial for diagnosing turbulence, since the direction of the energy transfer rate is found to be shaped by the local streamline topology. Compressible fluctuations, on the contrary, do not show a clear topological selection in the energy transfer since the overall direction of the local cascade rate is found to be determined by the sign of -del & centerdot; u (plasma volumetric compression or expansion).

The relaxation of many physical systems is constrained by collisions. However, most space and astrophysical plasmas are nearly collisionless, leaving open questions about the pathways of energy transfer and dissipation. In many turbulent plasmas, the electric field takes on the role of energy transfer leading to dissipation. Using measurements from the Magnetospheric Multiscale Mission, we study the statistical properties of the electric field spectrum in the kinetic range of strong turbulence generated by magnetic reconnection in the Earth's magnetotail. From the inertial to the kinetic range (often called the dissipation range) of scales, we find that turbulent fluctuations develop increasingly non-Gaussian features. The kinetic range contains two regimes with distinct behaviors in the power spectrum and measures of non-Gaussianity. In the subelectron kinetic regime (smaller than the electron gyroradius), the turbulence becomes isotropic and exhibits energy equipartition between the electric field and magnetic field. Our analyses indicate (1) a growing presence of intermittent structures that are expected to lead to enhanced energy dissipation, (2) changes in the electric field dynamics at the transitions between turbulence regimes, and (3) an asymptotic relaxation to a state of energy equipartition in the electromagnetic field in the subelectron kinetic range, where the energy transfer between the magnetic and electric fields appears to be near complete. These results reveal the importance of the electric field in mediating turbulence dissipation and relaxation in collisionless plasmas.

Geomagnetic field reversal sequences exhibit persistence times spanning a broad range, from a few 10^4 years to superchrons lasting more than 10^7 years. Despite extensive observational and theoretical work, the physical mechanisms governing how such reversals occur and how their broad temporal variability is organized are still not fully understood. Here we investigate the temporal variability of geomagnetic polarity in a thermally driven low-dimensional geodynamo model subject to a slow periodic modulation of the control parameter governing the large-scale induction, namely the α-effect parameter. We find that the modulation generates a multipeaked probability density function of magnetic persistence times, with local maxima occurring at approximately integer multiples of the modulation timescale, as expected in a stochastic-resonance-like regime. The peak positions follow an approximately linear dependence on their index, showing that the characteristic timescales selected by the system are set by the imposed modulation period. These results provide a physically motivated numerical framework in which slow modulation of a geodynamo control parameter can organize reversal statistics through stochastic-resonance-like dynamics.

The study of the statistics of gradient tensors’ invariants is useful to characterize the morphological/topological features of magnetic flux and plasma velocity flow lines in turbulent space plasmas. In the recent past, some studies of the statistics of the gradient tensors’ invariants have been done to investigate the velocity and magnetic field flow lines topologies in turbulent heliospheric plasmas, thanks to the availability of multipoint missions. Here, we present a novel/complementary approach to the characterization of the gradient tensor properties of velocity and magnetic field in plasmas based on Schur decomposition of the field gradient tensors. This decomposition can be seen as an alternative to the standard decomposition into symmetric and skew-symmetric components, allowing for a decomposition of gradients into normal and nonnormal parts , separating eigenvalue and ideal pressure terms from the deviatoric and dissipative ones. The method is preliminarily applied to observations from the NASA Magnetospheric Multiscale space mission in the solar wind and the magnetosheath to show its potentiality.

We examine how local streamline topology and energy cascade rate self-organize in plasma turbulence for both compressible and incompressible regimes. Using a fully-compressible Hall-magnetohydrodynamic simulation, we quantify the subgrid-scale energy transfer and analyze its relationship to streamline structures by means of grandient tensor geometric invariants of the velocity field. Our results highlight how streamline topology is crucial for diagnosing turbulence: for nearly-incompressible fluctuations the energy is primarily transferred to smaller scales through strain-dominated and stable-vortical structures, while is back-transferred towards larger scales through unstable-vortical structures. Compressible fluctuations, on the contrary, do not show a clear topological selection of the energy transfer since the overall direction of the local cascade rate is found to be determined by the sign of -∇· u (plasma volumetric compression or expansion).

Understanding the spatio-temporal organization of geomagnetic field variations during intense magnetic storms is essential for characterizing the large-scale response of the magnetosphere–ionosphere system. In this study, we investigate the temporal evolution of geomagnetic field correlations using a network-based approach applied to ground-based observations.We consider minute-resolution magnetic field data recorded by 50 geomagnetic observatories located in the Northern Hemisphere at magnetic latitudes higher than 40°. The analysis focuses on the temporal behavior of the horizontal component of the geomagnetic field during the intense magnetic storm that occurred in May 2024. A functional network is constructed by quantifying the statistical relationships between pairs of observatories over sliding time windows, allowing the connectivity structure of the network to evolve in time.The network properties are analyzed using standard metrics from complex network theory with the aim of characterizing changes in the network topology between geomagnetically quiet conditions and storm periods. By comparing the network structure before, during, and after the storm main phase, this study aims to identify collective patterns and large-scale reconfigurations in geomagnetic field dynamics at high latitudes.This work explores the potential of network analysis as a complementary tool for investigating geomagnetic storms using multi-station ground-based observations, providing insights into the complex/collective behavior of the geomagnetic field variations during extreme space weather events.This research was funded 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.

A notable feature of turbulence in solar wind is the presence of an additional power-law spectral domain at scales below the ion inertial length. This spectral domain has been attributed to a distinct turbulent regime involving alternative wave modes. However, this interpretation is still up for debate, as is the occurrence of dissipation at these scales. Here, we present a methodology to investigate the irreversible dynamics and the lack of detailed balance for the energy of magnetic field fluctuations at ion/sub-ion scales via the asymmetric time-correlation function using high-resolution magnetic field measurements from the Parker Solar Probe mission. The preliminary results are discussed in relation to irreversibility and dissipation at ion/sub-ion scales.

The Automatics in SpAce exploration (ASAP) project has as a goal the design and development of Machine Learning algorithms for the automation of operations to be implemented on the on-board processors of space missions. In the framework of ASAP a set of ML algorithms for on-board science operations of space missions have been developed/optimized on consumer-grade computing systems to be further selected for orting of existent ML models directly on an FPGA prototype. In more detail, algorithms pertaining to four main use cases have been considered: the autonomous triggering of special measurement modes and the selective downlink of plasma environment parameters; the advanced on-board data analysis of three-dimensional particle distribution functions; the on-board analysis of solar images; the on-board prediction capability of SEP related hazards. Here we describe the algorithms, their performances and requirements for the on-board implementation. ASAP has received funding from the EU’s HORIZON Research and Innovation Action (GA no.101082633)

The characterization of the complex topologies of magnetic and velocity field in turbulent space plasmas benefits from the analysis of the statistics of the gradient tensor invariants. In this work, we evaluate the relative weight of the various terms present in the evolution equation for the velocity (Q and R) and magnetic (X and Y) field gradient tensors invariants, so to establish which is the more appropriate dynamical regime governing the evolution of the magnetic and velocity field line topology. The quantities Q, R, X and Y are related to the characteristic polynomial of the velocity (Q and R quantities) and magnetic (X and Y invariants) fields’ gradient tensors. These four quantities are invariant under transformations of the SO(3)-group. The study is performed using data from both the NASA-MMS mission and direct numerical simulations. In particular, we show how in the solar wind and magnetosheath plasma turbulence the evolution of the velocity field gradient tensor invariants is controlled by different dominant terms. This result is discussed in connection with the different regimes of the observed turbulence, thus providing an alternative approach to the traditional methods used to investigate space plasma turbulence.

This article presents a concise overview of research developments and advancements in space weather and space climate, with a specific focus on the significant contributions made by members of the Italian Space Weather Community (SWICo). We highlight their achievements in instrument development, observational techniques, and modeling. Furthermore, we introduce a special collection of papers within this journal, entitled “Frontiers in Italian Studies on Space Weather and Space Climate.” This collection features a selection of research articles and presentations from the Second and Third SWICo Congresses, held in Rome in February 2022 and November 2024, respectively, and hosted by the Italian Space Agency.

The Gannon Storm, also known as the Mother's Day Storm of May 2024, ranks among the most intense geomagnetic disturbances of the space age, triggered by a powerful interplanetary coronal mass ejection. Leveraging data from over 100 globally distributed magnetic observatories, this study provides a detailed analysis of its ground-level impacts, focusing on the horizontal and vertical components of the magnetic field and the rate of change of horizontal intensity (dH/dt) $(dH/dt)$. Global and polar maps reveal the equatorward expansion of auroral electrojets, asymmetric ring current dynamics, and significant regional variations in geomagnetic responses. Rapid dH/dt $dH/dt$ variations, a key proxy for geomagnetically induced currents, pinpoint regions potentially at risk. This study provides a detailed characterization of the ground-level impacts of this superstorm.

The dynamics of the Earth's magnetosphere/ionosphere system is remarkably complex, particularly in response to changes of the solar wind and interplanetary conditions. This interplay between the Earth's magnetic field and the solar wind generates a highly complex dynamics. The interaction between the interplanetary medium and the Earth's magnetosphere triggers significant changes within the magnetosphere/ionosphere system. These alterations can lead to various phenomena, including magnetospheric substorms, which exhibit an avalanche dynamics and scale-free energy dissipation. This complex behavior resembles crackling noise phenomena observed in certain physical systems. By examining the scaling properties of auroral electrojet AL-index bursts during these substorms, we have identified similarities with crackling noise in front propagation models. Furthermore, our investigation has unveiled a scaling function describing the avalanche profile of the AL-index, shedding light on the underlying mechanisms governing these bursty dynamics. These findings significantly contribute to our understanding of magnetospheric plasma sheet dynamics and the mechanisms behind the magnetospheric substorms. By linking the scale-free characteristics of these bursts to crackling noise behavior, we gain valuable insights into the underlying physics governing these complex phenomena within Earth's magnetosphere/ionosphere system.

Irreversibility and the processes occurring at ion and sub-ion scales are key challenges in understanding energy dissipation in non-collisional space plasmas. Recent advances have significantly improved the characterization of irreversibility and energy transfer across scales in turbulent fluid-like media, using high-order correlation functions and testing the validity of certain fluctuation relations. In this study, we explore irreversibility at non-MHD scales during a magnetospheric current disruption event. Our approach involves analyzing the asymmetric correlation function, assessing the validity of a fluctuation relation, and investigating delayed coupling between different scales to reveal evidence of a cascading mechanism. The results clearly demonstrate the irreversible nature of fluctuations at ion and sub-ion scales. Additionally, we provide potential evidence for an energy cascading mechanism occurring over short time delays.

Space plasma turbulence plays a relevant role in several plasma environments, such as solar wind and the Earth’s magnetosphere–ionosphere system, and is essential for describing their complex coupling. This interaction gives rise to various phenomena, including ionospheric irregularities and the amplification of magnetospheric and ionospheric currents. The structure and dynamics of these currents have relevant implications, for example, in studying ionospheric heating and the nature of electric and magnetic field fluctuations in the auroral and polar environments. In this study, we investigate the nature of small-scale fluctuations characterizing the ionospheric magnetic field in response to different geomagnetic conditions. We use high-resolution (50 Hz) magnetic data from the ESA’s Swarm mission, collected during a series of high-latitude crossings, to probe the scaling features of magnetic field fluctuations in auroral and polar cap regions at spatial scales still poorly explored. Our findings reveal that magnetic field fluctuations in field-aligned currents (FACs) and polar cap regions across both hemispheres are characterized by different scaling properties, suggesting a distinct driver of turbulence. Furthermore, we find that geomagnetic activity significantly influences the nature of energy dissipation in FAC regions, leading to more localized filamentary structures toward smaller scales.

Ionospheric plasma density irregularities, which are one of the primary sources of disturbance for the Global Navigation Satellite System, significantly impact the propagation of electromagnetic signals, leading to signal degradation and potential interruptions. In the equatorial ionospheric F region after sunset, certain plasma density irregularities, identified as equatorial plasma bubbles, encounter optimal conditions for their formation and development. The energy spectra of electron density fluctuations associated with these irregularities exhibit a power-law scaling behavior qualitatively similar to the Kolmogorov power law observed in fluid turbulence theory. This intriguing similarity raises the possibility that these plasma density irregularities may possess turbulent characteristics. In this study, we analyzed electron density, temperature, and pressure data obtained from the China Seismo-Electromagnetic Satellite (CSES-01) to delve into the spectral properties of equatorial plasma depletions in the ionospheric F region at an altitude of about 500 km. This research marks the first exploration of these properties utilizing CSES-01 data and focuses on 14 semi-orbits that crossed the equator after midnight (01:00–03:00 LT), characterized by a geomagnetic quiet condition (Kp < 1). The analysis of electron temperature, density and pressure within equatorial plasma depletions revealed power-law scaling behavior for all the selected parameters. Notably, the spectral index values of these parameters are different from each other. The significance of these findings in terms of investigating plasma depletions via magnetic field signatures, as well as their relationship to the occurrence of Rayleigh–Taylor convective turbulence, is examined and discussed.

Context. Kinetic-scale dynamics in weakly collisional space plasmas usually exhibits a self-similar statistics of magnetic field fluctuations. This implies the existence of an invariant probability density function (master curve). Aims. We provide an analytical derivation of the master curve by assuming that perpendicular fluctuations can be modeled through a scale-dependent Langevin equation. Methods. In our model, magnetic field fluctuations are the stochastic variable, and their scale-to-scale evolution is assumed to be a Langevin process. We propose a formal derivation of the master curve describing the statistics of the fluctuations at kinetic scales. The model predictions were tested on independent data samples of the fast solar wind measured near the Sun by Parker Solar Probe and near the Earth by Cluster. Results. The master curve is a generalization of the Kappa distribution with two parameters: One parameter regulates the tails, and the other controls the asymmetry. The model predictions match the spacecraft observations up to 5 sigma and even beyond in the case of perpendicular magnetic field fluctuations.

The study of the physical properties of the topside ionosphere is fundamental to investigating the energy balance of the ionosphere and developing accurate models to predict relevant phenomena, which are often at the root of Space Weather effects in the near-Earth environment. One of the most important physical parameters characterising the ionospheric medium is electrical conductivity, which is crucial for the onset and amplification of ionospheric currents and for calculating the power density dissipated by such currents. We characterise, for the first time, electrical conductivity in the direction perpendicular to the geomagnetic field, namely Pedersen and Hall conductivities, in the topside ionosphere at an altitude of about 450 km. For this purpose, we use eight years of in situ simultaneous measurements of electron density, electron temperature and geomagnetic field strength acquired by the Swarm A satellite. We present global statistical maps of perpendicular electrical conductivity and study their variations depending on magnetic latitude and local time, seasons, and solar activity. Our findings indicate that the most prominent features of perpendicular electrical conductivity are located at low latitudes and are probably driven by the complex dynamics of the Equatorial Ionisation Anomaly. At higher latitudes, perpendicular conductivity is a few orders of magnitude lower than that at low latitudes. Nevertheless, conductivity features are modulated by solar activity and seasonal variations at all latitudes.