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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 simulationThese waves exhibit lower intensity within the magnetosphere at noon, compared to the prenoon and postnoon sectorsPc2 waves observed in the simulation are associated with largest and fast moving flux transfer events initiated by subsolar reconnection [ABSTRACT FROM AUTHOR]

Vlasiator is a high‐performance ion‐kinetic code that is now conducting 3D hybrid‐Vlasov simulations of the global magnetosphere. We use Vlasiator to investigate the impact of a pressure pulse with southward‐oriented magnetic field on the Earth's magnetosphere. The simulation driving parameters are comparable to conditions that have led to geomagnetic storms. Our pressure pulse simulation reproduces many physical effects, namely the expansion of the auroral oval, the development of field‐aligned currents, enhanced particle precipitation near the open/closed field line boundary, and compression of Earth's magnetopause. This demonstrates the effectiveness of the hybrid‐Vlasov approach for moderate driving conditions. Our investigation of the time‐dependent magnetopause compression motivates a generalization of the existing theory. Specifically, we find that accounting for the finite transition time of the solar wind dynamic pressure improves the model's description of the magnetopause oscillations. Plain Language Summary: We perform state‐of‐the‐art simulations of the interaction of near‐Earth space environment with the incoming material ejected from the Sun. The response of Earth's magnetic field to such ejecta is known as a "geomagnetic storm." Our simulation approach captures the motion of protons more accurately than commonly used fluid models, but at the cost of making the simulations more computationally intensive. To validate this novel approach, we compare the output of our simulation with established observational signatures of the initial storm phase. We find that our simulation, of relatively moderate storm conditions, reproduces known effects that are relevant to society. Such effects include particle precipitation into the atmosphere and reconfiguration of global magnetic field. Our simulation does diverge from established models on how the magnetopause, the boundary between Earth's magnetic environment and the solar wind, moves in response to a sudden increase of incoming pressure. This inspires a modification of the theory of magnetopause motion, which better accounts for the detailed time profile of the incoming solar wind. Key Points: Vlasiator's 3D hybrid‐kinetic model of the global magnetosphere produces expected behavior for a pressure pulse arriving at EarthThe finite transition time of the pressure pulse causes magnetopause oscillations to be weak and elongated relative to established modelsThe magnetopause oscillations are explained with a generalized model that accounts for the finite transition time of the pressure pulse [ABSTRACT FROM AUTHOR]

Geospace plasma simulations have progressed toward more realistic descriptions of the solar wind–magnetosphere interaction from magnetohydrodynamic to hybrid ion‐kinetic, such as the state‐of‐the‐art Vlasiator model. Despite computational advances, electron scales have been out of reach in a global setting. eVlasiator, a novel Vlasiator submodule, shows for the first time how electromagnetic fields driven by global hybrid‐ion kinetics influence electrons, resulting in kinetic signatures. We analyze simulated electron distributions associated with reconnection sites and compare them with Magnetospheric Multiscale (MMS) spacecraft observations. Comparison with MMS shows that key electron features, such as reconnection inflows, heated outflows, flat‐top distributions, and bidirectional streaming, are in remarkable agreement. Thus, we show that many reconnection‐related features can be reproduced despite strongly truncated electron physics and an ion‐scale spatial resolution. Ion‐scale dynamics and ion‐driven magnetic fields are shown to be significantly responsible for the environment that produces electron dynamics observed by spacecraft in near‐Earth plasmas. Plain Language Summary: The near‐Earth space environment is driven by the solar wind, a thin mixture of ions (mostly protons) and electrons carrying the magnetic field of the Sun. The interaction of this plasma with the Earth's magnetic field produces space weather phenomena, such as aurorae and geomagnetic storms. Supercomputer simulations are an invaluable tool in studying the environment, providing a global view of our magnetosphere—as far as there is enough computational power to resolve the relevant physical processes. Modern simulation codes, such as Vlasiator, can model the environment in great detail at least for the behavior of the ions, providing new insights beyond previous fluid‐scale models. However, detailed electron physics is required to fully understand the near‐Earth space environment at microscales, especially at reconnection sites where the magnetic fields from the Earth and Sun interact. This work uses the new eVlasiator module of Vlasiator to probe electron physics on a global scale, showing electron behavior that is consistent with satellite observations at several locations. Key Points: We present a survey of kinetic electron distribution functions in a global Vlasov model of the Earth's magnetosphereIon‐scale background fields yield electron distributions consistent with Magnetospheric Multiscale observationsParallel electric fields are observed at the magnetopause, coincident with a flat‐top electron distribution [ABSTRACT FROM AUTHOR]

We study the interaction of upstream ultralow frequency (ULF) waves with collisionless shocks by analyzing the outputs of 11 2D local hybrid simulation runs. Our simulated shocks have Alfvénic Mach numbers between 4.29 and 7.42 and their θBN angles are 15°, 30°, 45°, and 50°. The ULF wave foreshocks develop upstream of all of them. The wavelength and the amplitude of the upstream waves exhibit a complex dependence on the shock's MA and θBN. The wavelength positively correlates with both parameters, with the dependence on θBN being much stronger. The amplitude of the ULF waves is proportional to the product of the reflected beam velocity and density, which also depend on MA and θBN. The interaction of the ULF waves with the shock causes large‐scale (several tens of upstream ion inertial lengths) shock rippling. The properties of the shock ripples are related to the ULF wave properties, namely their wavelength and amplitude. In turn, the ripples have a large impact on the ULF wave transmission across the shock because they change local shock properties (θBN, strength), so that different sections of the same ULF wavefront encounter shock with different characteristics. Downstream fluctuations do not resemble the upstream waves in terms the wavefront extension, orientation or their wavelength. However, some features are conserved in the Fourier spectra of downstream compressive waves that present a bump or flattening at wavelengths approximately corresponding to those of the upstream ULF waves. In the transverse downstream spectra, these features are weaker. Plain Language Summary: We address the problem of what happens to upstream ultralow frequency (ULF) waves as they reach shocks and are carried into the downstream region. We do this by analyzing the results of 11 2.5D local hybrid simulations of collisionless shocks. We find that the waves are not simply transmitted into the downstream region but that their identity is largely destroyed, as the downstream fluctuations do not resemble the upstream waves neither in wavelengths nor in appearance. However, some features observed in the Fourier spectra of upstream ULF waves are conserved in the Fourier spectra of compressive downstream fluctuations. Key Points: Upstream ultralow frequency (ULF) waves are not simply transmitted across collisionless shocksSome spectral features of compressive upstream ULF waves are conserved in the spectra of downstream fluctuationsThere is some correlation between the properties of the shock ripples and the foreshock ULF waves [ABSTRACT FROM AUTHOR]

Earth's magnetosheath consists of shocked solar wind plasma that has been compressed and slowed down at the Earth's bow shock. Magnetosheath jets are pulses of enhanced dynamic pressure in the magnetosheath. Jets have been observed by numerous spacecraft missions, but their origin has remained unconfirmed, though several formation mechanisms have been suggested. In this study, we use a method for automatically identifying and tracking jets as well as foreshock compressive structures (FCSs) in four 2D runs of the global hybrid‐Vlasov simulation Vlasiator. We find that up to 75% of magnetosheath jets are caused by FCSs impacting the bow shock. These jets propagate deeper into the magnetosheath than the remaining 25% of jets that are not caused by FCSs. We conduct a visual case study of one jet that was not caused by FCSs and find that the bow shock was not rippled before the formation of the jet. Plain Language Summary: The space around Earth is filled with plasma, the fourth state of matter. Earth's magnetic field shields our planet from the stream of plasma coming from the Sun, the solar wind. The solar wind plasma is slowed down at the Earth's bow shock, before it flows against and around the Earth's magnetic field in the magnetosheath. Sometimes, pulses of high density or velocity can occur in the magnetosheath that have the potential to disturb the inner regions of near‐Earth space where many spacecraft orbit. We call these pulses magnetosheath jets. Magnetosheath jets have been observed by many spacecraft over the past few decades, but how they form has remained unclear. In this study, we use the Vlasiator model to simulate plasma in near‐Earth space and investigate the origins of magnetosheath jets. We find that the formation of up to 75% of these jets can be explained by compressive structures in the foreshock, a region populated by intense wave activity extending sunward of the quasi‐parallel bow shock, where interplanetary magnetic field lines allow shock‐reflected particles to travel back toward the Sun. Key Points: We investigated magnetosheath jets in four hybrid‐Vlasov simulation runs with different solar wind parametersForeshock compressive structures can explain the formation of up to 75% of magnetosheath jetsThe foreshock compressive structure‐caused jets travel deeper into the magnetosheath than the 25% of the jets whose origins remain unclear [ABSTRACT FROM AUTHOR]

The foreshock, extending upstream of Earth's bow shock, is a region of intense electromagnetic wave activity and nonlinear phenomena, which can have global effects on geospace. It is also the first geophysical region encountered by solar wind disturbances journeying toward Earth. Here, we present the first observations of considerable modifications of the foreshock wave field during extreme events of solar origin called magnetic clouds. Cluster's multispacecraft data reveal that the typical quasi‐monochromatic foreshock waves can be completely replaced by a superposition of waves each with shorter correlation lengths. Global numerical simulations further confirm that the foreshock wave field is more intricate and organized at smaller scales. Ion measurements suggest that changes in shock‐reflected particle properties may cause these modifications of the wave field. This state of the foreshock is encountered only during extreme events at Earth, but intense magnetic fields are typical close to the Sun or other stars. Plain Language Summary: Solar storms are giant clouds of particles ejected from the Sun into space during solar eruptions. When solar storms are directed toward Earth, they can cause large disturbances in near‐Earth space, for example, disrupting communications or damaging spacecraft electronics. Understanding in detail what happens when solar storms reach Earth is crucial to mitigate their effects. Using measurements from the Cluster spacecraft, we investigate how solar storms modify the properties of the very first region of near‐Earth space they encounter when journeying toward Earth. This region, called the foreshock, extends ahead of the protective bubble formed by the Earth's magnetic field, the magnetosphere. The foreshock is home to intense electromagnetic waves, and disturbances in this region can perturb the Earth's magnetosphere. Our study reveals that solar storms modify profoundly the foreshock, resulting in a more complex wave activity. Global numerical simulations performed with the Vlasiator code confirm our findings. These changes could affect the regions of space closer to Earth, for example, in modifying the wave properties or the amount of solar particles entering the Earth's magnetosphere. This needs to be taken into account to better anticipate the effects of solar storms at Earth. Key Points: When reaching geospace, magnetic clouds modify significantly the properties of the first geophysical region they encounter, the foreshockTypical quasi‐monochromatic foreshock waves are replaced by a superposition of waves at different periods with a shorter transverse extentMultiple field‐aligned beams observed during one event suggest a link between the multiple wave periods and the suprathermal ion properties [ABSTRACT FROM AUTHOR]

This paper describes properties and behavior of magnetic reconnection and flux transfer events (FTEs) on the dayside magnetopause using the global hybrid‐Vlasov code Vlasiator. We investigate two simulation runs with and without a sunward (positive) Bx component of the interplanetary magnetic field (IMF) when the IMF is southward. The runs are two‐dimensional in real space in the noon‐midnight meridional (polar) plane and three‐dimensional in velocity space. Solar wind input parameters are identical in the two simulations with the exception that the IMF is purely southward in one but tilted 45° toward the Sun in the other. In the purely southward case (i.e., without Bx) the magnitude of the magnetosheath magnetic field component tangential to the magnetopause is larger than in the run with a sunward tilt. This is because the shock normal is perpendicular to the IMF at the equatorial plane, whereas in the other run the shock configuration is oblique and a smaller fraction of the total IMF strength is compressed at the shock crossing. Hence, the measured average and maximum reconnection rate are larger in the purely southward run. The run with tilted IMF also exhibits a north‐south asymmetry in the tangential magnetic field caused by the different angle between the IMF and the bow shock normal north and south of the equator. Greater north‐south asymmetries are seen in the FTE occurrence rate, size, and velocity as well; FTEs moving toward the Southern Hemisphere are larger in size and observed less frequently than FTEs in the Northern Hemisphere. Key Points: Sunward IMF tilt results in a smaller tangential field at the magnetopause, slowing dayside reconnectionSmaller tangential field results from a decrease in the IMF component that is shocked up at the bow shockA positive IMF Bx component introduces north‐south asymmetries, where fewer (but larger) FTEs appear on the Southern Hemisphere [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present a detailed study of the effects of the interplanetary magnetic field (IMF) strength on the foreshock properties at small and large scales. Two simulation runs performed with the hybrid‐Vlasov code Vlasiator with identical setup but with different IMF strengths, namely, 5 and 10 nT, are compared. We find that the bow shock position and shape are roughly identical in both runs, due to the quasi‐radial IMF orientation, in agreement with previous magnetohydrodynamic simulations and theory. Foreshock waves develop in a broader region in the higher IMF strength run, which we attribute to the larger growth rate of the waves. The velocity of field‐aligned beams remains essentially the same, but their density is generally lower when the IMF strength increases, due to the lower Mach number. Also, we identify in the regular IMF strength run ridges of suprathermal ions which disappear at higher IMF strength. These structures may be a new signature of the foreshock compressional boundary. The foreshock wave field is structured over smaller scales in higher IMF conditions, due to both the period of the foreshock waves and the transverse extent of the wave fronts being smaller. While the foreshock is mostly permeated by monochromatic waves at typical IMF strength, we find that magnetosonic waves at different frequencies coexist in the other run. They are generated by multiple beams of suprathermal ions, while only a single beam is observed at typical IMF strength. The consequences of these differences for solar wind‐magnetosphere coupling are discussed. [ABSTRACT FROM AUTHOR]

Abstract: We report ion acceleration by flux transfer events in the terrestrial magnetosheath in a global two‐dimensional hybrid‐Vlasov polar plane simulation of Earth's solar wind interaction. In the model we find that propagating flux transfer events created in magnetic reconnection at the dayside magnetopause drive fast‐mode bow waves in the magnetosheath, which accelerate ions in the shocked solar wind flow. The acceleration at the bow waves is caused by a shock drift‐like acceleration process under stationary solar wind and interplanetary magnetic field upstream conditions. Thus, the energization is not externally driven but results from plasma dynamics within the magnetosheath. Energetic proton populations reach the energy of 30 keV, and their velocity distributions resemble time‐energy dispersive ion injections observed by the Cluster spacecraft in the magnetosheath. [ABSTRACT FROM AUTHOR]