Explore the vast range of titles available.

The Earth’s magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth’s surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.The Earth’s bow shock results from the interaction of the solar wind with the terrestrial magnetic field. With global numerical simulations and spacecraft observations, the transmission of fast magnetosonic waves through the bow shock is revealed.

Magnetic reconnection and current sheet kink instability often develop concurrently in current sheets, yet their dynamic interplay remains unclear. We investigate their interaction in the magnetotail of a 3D global magnetospheric hybrid‐Vlasov simulation. We identify the instability growth and saturation phase and estimate the evolution of the reconnection rate during the same interval. Our findings indicate that the reconnection rate decreases during the instability growth phase, especially at locations where the current sheet undergoes significant perturbations. These results highlight the intricate three‐dimensional relationship between reconnection and kink instabilities, suggesting that the kink instability plays a significant role in modulating the reconnection rate. Plain Language Summary Magnetic reconnection is a fundamental process in plasmas during which magnetic field energy is transferred, often explosively, to plasma particles. Magnetic reconnection develops in current sheets—extended regions of enhanced electric currents that are ubiquitous in plasmas. Current sheets are also the natural seedbed of plasma instabilities leading to wave generation. Among plasma instabilities, the current sheet kink instability causes the current sheet to distort and bend. Kink‐like distortions of the current sheet have been observed in a variety of plasmas, notably in the Earth's magnetotail (the region extending on the night side of the Earth's magnetosphere). While the kink instability and magnetic reconnection occur together in current sheets such as the magnetotail, their interaction is not well understood. We use a numerical simulation modeling the whole Earth's magnetosphere to investigate the interaction of the two processes in three dimensions. We find that as the kink waves grow, magnetic reconnection slows down, especially at locations where the current sheet is highly disturbed. Our findings suggest that the kink instability significantly affects magnetic reconnection. This study provides a deeper understanding of the intricate relationship between these two important phenomena. Key Points We investigate the interaction of magnetic reconnection and kink instability in a 3D global hybrid‐Vlasov simulation of near‐Earth space Magnetic reconnection is ongoing in the Earth's magnetotail during the growth and saturation phases of the kink instability The reconnection rate decreases during the instability growth phase, especially where the current sheet undergoes significant perturbation

Flux transfer events (FTEs) are transient magnetic flux ropes at Earth's dayside magnetopause formed due to magnetic reconnection. As they move across the magnetopause surface, they can generate disturbances in the ultralow frequency (ULF) range, which then propagate into the magnetosphere. This study provides evidence of ULF waves in the Pc2 wave frequency range (>0.1 Hz) caused by FTEs during dayside reconnection using a global 3D hybrid‐Vlasov simulation (Vlasiator). These waves resulted from FTE formation and propagation at the magnetopause are particularly associated with large, rapidly moving FTEs. The wave power is stronger in the morning than afternoon, showing local time asymmetry. In the pre and postnoon equatorial regions, significant poloidal and toroidal components are present alongside the compressional component. The noon sector, with fewer FTEs, has lower wave power and limited magnetospheric propagation. Plain Language Summary The Earth's magnetosphere is a dynamic region shaped by the interplay between the solar wind and Earth's magnetic field. This interaction occurs at the boundary of the magnetosphere (magnetopause) through a process known as magnetic reconnection, giving rise to Flux Transfer Events (FTEs), which are magnetic structures that carry flux and energy into the magnetosphere. These FTEs form either in sudden bursts, patchy patterns or in a continuous, and relatively stable way making the magnetopause surface dynamic. As the FTEs move along the boundary of the magnetosphere, they create compressed regions and lead to wave generation that can extend into the magnetosphere. The study uses an advanced 3D hybrid‐Vlasov simulation model to analyze waves originated from FTE formation and propagation at the magnetopause. We find that rapidly moving and large FTEs have a significant impact on the magnetopause, leading to the generation of ULF waves with frequency above 0.1 Hz. This shows first direct evidence supporting previous theoretical speculations regarding the ability of FTEs to generate waves near the magnetopause. Key Points Dayside Pc2 waves (>0.1 Hz) have been detected in a 3D hybrid‐Vlasov simulation These waves exhibit lower intensity within the magnetosphere at noon, compared to the prenoon and postnoon sectors Pc2 waves observed in the simulation are associated with largest and fast moving flux transfer events initiated by subsolar reconnection

The foreshock region of a CME shock front, where shock accelerated electrons form a beam population in the otherwise quiescent plasma is generally assumed to be the source region of type II radio bursts. Nonlinear wave interaction of electrostatic waves excited by the beamed electrons are the prime candidates for the radio waves’ emission. To address the question whether a single, or two counterpropagating beam populations are a requirement for this process, we have conducted 2.5D particle-in-cell simulations using the fully relativistic ACRONYM code. Results show indications of three-wave interaction leading to electromagnetic emission at the fundamental and harmonic frequency for the two-beam case. For the single-beam case, no such signatures were detectable.

We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given in SI units without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30∘, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock through the magnetosheath. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending earthward from the bow shock by ∼2.6 RE, while its size perpendicular to the direction of propagation is ∼0.5 RE. We also investigate the jet evolution and find that the jet originates due to the interaction of the bow shock with a high-dynamic-pressure structure that reproduces observational features associated with a short, large-amplitude magnetic structure (SLAMS). The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies. To our knowledge, this paper therefore shows the first global kinetic simulation of a magnetosheath jet, which is in accordance with three observational jet criteria and is caused by a SLAMS advecting towards the bow shock.

The Dungey cycle is a fundamental process governing large-scale plasma dynamics in the near-Earth space, traditionally examined through Magnetohydrodynamic (MHD) simulations and ionospheric observations. However, MHD models often oversimplify the complexities of driving dynamics and kinetic processes, while observational data tend to lack sufficient coverage. In this study, we utilize a hybrid-Vlasov simulation to investigate the Dungey cycle, and introduce a novel method for quantifying reconnection voltages in different Magnetic Local Time (MLT) sectors. This method is validated by comparing it with the ionospheric open flux change rate in the simulation. Our analysis identifies discrete azimuthal convection channels of closed field lines, clearly initiated by dayside reconnection and propagating to the nightside. These channels are prominent even during intervals of intense nightside reconnection. Notably, we observe that the effective length of dayside reconnection fluctuates, even under steady solar wind conditions. Our results reveal significant deviations from MHD theory, which predicts that plasma flows within the magnetosphere should follow flux tube entropy isocontours. Instead, we demonstrate that plasma flows near reconnection sites and at the terminators deviate from isentropic behavior, suggesting the presence of non-adiabatic processes in these regions. This study validates the representation of the Dungey cycle in the Vlasiator 3D simulation and enhances our understanding of global plasma convection. Future work should focus on identifying the kinetic processes that explain the deviations in the plasma convection with flux tube entropy isocontours between MHD theory and kinetic approach.

Conductances are key properties of the ionospheric electrodynamics and the difficulty of measuring them directly is a significant limitation to the usefulness of many analysis techniques. We have utilized all available field-aligned observations from the EISCAT incoherent scatter ultra-high frequency (UHF) radar since 2001 and from the 42 m EISCAT Svalbard Radar (ESR) since 1998 to develop a new empirical model for estimating the high-latitude ionospheric Hall and Pedersen conductances. The solar radiation component of the model is parametrized with the solar zenith angle and the F10.7 index, and the auroral precipitation component is parametrized with the magnetic local time and the divergence-free part of the horizontal ionospheric current density, which is obtained from ground-based magnetic field observations. We have also derived a new technique based on spherical elementary current systems that can be used to solve for the ionospheric potential electric field and field-aligned current density from known ionospheric conductances and ground-based magnetic field observations, taking into account induction in the ionosphere and in the ground. The new empirical conductance model and solver were applied to IMAGE magnetometer network observations. Comparison of the results with Swarm and Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite observations showed reasonable agreement in the electric field profile and direction of the field-aligned current, but in the post-midnight sector the modelled amplitudes tended to be weaker than observations. The combination of the new conductance model and analysis technique allows estimating the key properties of ionospheric electrodynamics from ground-based magnetic field observations.

Bursty Bulk Flows (BBFs) are transient plasma flows in the Earth's magnetotail plasma sheet. These short-lived, high-speed flows play a key role in the magnetosphere-ionosphere coupling. Currently, most insights into the ionospheric signatures of BBFs come from individual case studies that include conjugate observations of BBFs in the magnetotail and field-aligned currents (FACs) in the nightside ionosphere. In this study, we utilise the 6D hybrid-Vlasov simulations to study the ionospheric signatures of BBFs in the near-Earth magnetotail. We show that a BBF with Vx≥400 km s−1 emerges shortly after magnetic reconnection occurs on the duskside at a radial distance between 11 and 14 RE (where RE=6371 km is the radius of the Earth) in the current sheet. As the BBF moves Earthward, clockwise (counterclockwise) flow vortices are induced on its dawn (dusk) sides. These vortical flows generate FACs flowing upward (out of the current sheet) on the dawnside and downward (into the current sheet) on the duskside flank, respectively. The mapping of BBF structures onto the ionosphere shows that the structure is primarily aligned in the east-west direction, with its ionospheric signatures appearing as enhancements in FACs, ionospheric conductances, horizontal ionospheric currents, energies of precipitating electrons and protons, and the formation of localised plasma flow channels. The upward and downward FACs associated with BBFs in the magnetotail consistently map to enhanced Region 2 (R2) and Region 1 (R1) FAC structures at ionospheric altitude, which are then closed in the ionosphere by north-west flowing Pedersen currents. The ionospheric counterpart of the Earthward plasma flow of the BBF is a channel of equatorward plasma flow, while the westward drift of these enhanced structures corresponds to the duskward motion of the BBF in the magnetotail.

Magnetic flux ropes are helical structures of magnetic field which form in a variety of magnetized plasmas. In near-Earth space, flux ropes are a manifestation of energy transfer at the magnetopause and in the magnetotail current sheet. We present a new method to detect magnetic flux ropes in large-scale simulations using only magnetic field line tracing. The method does not require prior identification of structures of interest such as current sheets or null lines and thus allows one to identify flux ropes of any size and orientation anywhere in the simulation domain. In this work, the new method is implemented in the hybrid-Vlasov model Vlasiator and demonstrated in global simulations of the terrestrial magnetosphere. We study the evolution of flux ropes forming during flux transfer events on the dayside magnetopause under a southward interplanetary magnetic field. It is found that flux ropes with an axial orientation along the dawn–dusk direction and propagating beyond the cusps will rapidly reconnect with the lobe magnetic field and vanish. In contrast, the flux ropes remaining near the equatorial plane and with an axial orientation along the flow direction – that is, tangential to the magnetopause – can maintain their structure and propagate tens of Earth radii down the tail in the absence of a reconnecting shear magnetic field component. These results are a step forward in the global characterization of flux ropes in and around the magnetosphere and may help in guiding the search for elusive far-tail flux ropes in satellite measurements.

We present results of noon–midnight meridional plane global hybrid-Vlasov simulations of the magnetotail ion dynamics under a steady southward interplanetary magnetic field using the Vlasiator model. The simulation results show magnetotail reconnection and formation of earthward and tailward fast plasma outflows. The hybrid-Vlasov approach allows us to study ion velocity distribution functions (VDFs) that are self-consistently formed during the magnetotail evolution. We examine the VDFs collected by virtual detectors placed along the equatorial magnetotail within earthward and tailward outflows and around the quasi-steady X line formed in the magnetotail at X≈-14RE. This allows us to follow the evolution of VDFs during earthward and tailward motion of reconnected flux tubes as well as study signatures of unmagnetized ion motion in the weak magnetic field near the X line. The VDFs indicate actions of Fermi-type and betatron acceleration mechanisms, ion acceleration by the reconnection electric field, and Speiser-type motion of ions near the X line. The simulated VDFs are compared and show good agreement with VDFs observed in the magnetotail by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. We find that the VDFs become more gyrotropic but retain transverse anisotropy and counterstreaming ion beams when being convected earthward. The presented global hybrid-Vlasov simulation results are valuable for understanding physical processes of ion acceleration during magnetotail reconnection, interpretation of in situ observations, and for future mission development by setting requirements on pitch angle and energy resolution of upcoming instruments.