Foreshock Bubbles (FBs) are large-scale transient structures found in Earth's foreshock region and are associated with foreshock-discontinuity interaction. FBs play a significant role in accelerating and energizing plasma through various mechanisms. In this study, we investigate the contribution of FBs to ion acceleration and energization by analyzing the key energy terms found in the equations that describe the temporal evolution of the kinetic and internal energy densities, namely, the pressure gradient term, the electromagnetic term and the pressure-strain term. To carry out this study, we employ the global hybrid-Vlasov simulation Vlasiator and compare our results with in situ observations from the Magnetospheric MultiScale mission. We find that FBs exhibit distinct signatures in the energy terms throughout their life cycles, from formation to decay as they interact with the bow shock. We show that the evolution of FBs involves complex energy conversions between electromagnetic, kinetic, and thermal energies. Notably, the energy term magnitudes increase during the initial phase of the FB, reach a peak, and subsequently decline as the FB dissipates, in agreement with previous studies. We find also strong energy conversion at the interface between the FB core and compressed edge due to the presence of a current sheet highlighting the complex contributions of the FB in accelerating and energizing ions.

Magnetic reconnection is a universal process that allows for the transfer and release of energy previously stored in a magnetic field configuration. At Earth, this process can occur in the boundary layer between Earth's magnetic field and the solar wind, called the magnetopause. This allows the magnetopause to act as the primary “entry gate” for the solar wind's energy into the Earth's magnetosphere and upper atmosphere. Along the magnetopause, magnetic reconnection is triggered inside diffusion regions: an electron diffusion region (EDR) embedded inside a larger ion diffusion region (IDR). Inside these diffusion regions, plasma decouples from the magnetic field, allowing the release of magnetic energy into the plasma. We identify a hitherto undefined region in the diffusion regions, which results from the interaction of demagnetized electrons in the EDR's reconnection current sheet and remagnetizing electrons in the IDR. We call this region the Diffusion Interaction Region. Using in situ Magnetospheric Multiscale plasma data and 2.5D particle‐in‐cell simulations, we isolate its defining features, which includes a significant parallel current structure and regions of parallel energy conversion. Defining this important and underexplored region of magnetic reconnection helps us determine how the local diffusion regions may couple with the large‐scale current structures within which they are embedded.

Magnetic reconnection is an explosive energy release event. It plays an important role in accelerating particles to high non‐thermal energies. These particles often exhibit energy spectra characterized by a power‐law distribution. However, the partitioning of energy between thermal and non‐thermal components, and between ions and electrons, remains unclear. This study provides estimates of energy partition based on a statistical analysis of magnetic reconnection events in Earth's magnetotail using data from the Magnetospheric Multiscale mission. Ions are up to 10 times more energetic than electrons but have softer spectra. We found for both ions and electrons that, as the average energy of particles (temperature) increases, their energy spectra become softer (steeper) and thus, the fraction of energy carried by the non‐thermal components decreases. These results challenge existing theories of particle acceleration through magnetotail reconnection.

Particles are heated efficiently through energy conversion processes, such as shocks and magnetic reconnection, in collisionless plasma environments. While empirical scaling laws for the temperature increase have been obtained, the precise mechanism of energy partition between ions and electrons remains unclear. Here we show, based on coupled theoretical and observational scaling analyses, that the temperature increase, Δ T , depends linearly on three factors: the available magnetic energy per particle, the Alfvén Mach number (or reconnection rate), and the characteristic spatial scale L . Based on statistical data sets obtained from Earth’s plasma environment, we find that L is on the order of: (1) the ion gyroradius for ion heating at shocks; (2) the ion inertial length for ion heating in magnetic reconnection; and (3) the hybrid inertial length for electron heating in both shocks and magnetic reconnection. With these scales, we derive the ion-to-electron ratios of temperature increases as Δ T i / Δ T e = ( 3 β i / 2 ) 1 / 2 ( m i / m e ) 1 / 4 for shocks and Δ T i / Δ T e = ( m i / m e ) 1 / 4 for magnetic reconnection, where β i is the ion plasma beta and m i and m e are the ion and electron particle masses, respectively. We anticipate that this study will serve as a starting point for a better understanding of particle heating in space plasmas, enabling more sophisticated modeling of its scaling and universality.

On April 24th, 2023, a CME event caused the solar wind to become sub-Alfvenic, leading to the development of an Alfven Wing configuration in the Earth's Magnetosphere. Alfven Wings have previously been observed as cavities of low flow in Jupiter's magnetosphere, but the observing satellites did not have the ability to directly measure the Alfven Wings' current structures. Through in situ measurements made by the Magnetospheric Multiscale (MMS) spacecraft, the April 24th event provides us with the first direct measurements of current structures during an Alfven Wing configuration. We have found two distinct types of current structures associated with the Alfven Wing transformation as well as the magnetosphere recovery. These structures are observed to be significantly more anti-field-aligned and electron-driven than typical magnetopause currents, indicating the disruptions caused to the magnetosphere current system by the Alfven Wing formation.

Fundamental processes in plasmas act to convert energies into different forms, for example, electromagnetic, kinetic and thermal. Direct derivation from the Vlasov-Maxwell equation yields sets of equations that describe the temporal evolution of magnetic, kinetic and internal energies in either the monofluid or multifluid frameworks. In this work, we focus on the main terms affecting the changes in kinetic energy. These are pressure-gradient-related terms and electromagnetic terms. The former account for plasma acceleration/deceleration from a pressure gradient, while the latter from an electric field. Although limited spatial and temporal deviations are expected, a statistical balance between these terms is fundamental to ensure the overall conservation of energy and momentum. We use in-situ observations from the Magnetospheric MultiScale (MMS) mission to study the relationship between these terms. We perform a statistical analysis of those parameters in the context of magnetic reconnection by focusing on small-scale Electron Diffusion Regions and large-scale Flux Transfer Events. The analysis reveals a correlation between the two terms in the monofluid force balance, and in the ion force and energy balance. However, the expected relationship cannot be verified from electron measurements. Generally, the pressure-gradient-related terms are smaller than their electromagnetic counterparts. We perform an error analysis to quantify the expected underestimation of gradient values as a function of the spacecraft separation compared to the gradient scale. Our findings highlight that MMS is capable of capturing energy and force balance for the ion fluid, but that care should be taken for energy conversion terms based on electron pressure gradients.

AbstractWe report a rare regime of Earth's magnetosphere interaction with sub‐Alfvénic solar wind in which the windsock‐like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low‐beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter‐streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic‐cloud and Alfvén‐wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub‐Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars.

Turbulence is a prevalent phenomenon in space and astrophysical plasmas, often characterized by stochastic fluctuations. While laboratory experiments and numerical simulations have revealed chaotic behavior, in situ observations of turbulent plasmas in natural environments have predominantly shown highly stochastic signatures. Here, we present unprecedented in situ evidence of chaotic fluctuations in the turbulent solar wind plasma downstream of the Earth's bow shock. By analyzing the relative location of magnetic-field fluctuations on the permutation entropy-complexity plane, we demonstrate that turbulence in the magnetosheath plasma exhibits characteristics of chaotic fluctuations rather than stochastic behavior, diverging from the expected traits of well-developed turbulence. This finding challenges established notions of plasma turbulence and reveals the need for caution when using the magnetosheath as a laboratory for studying plasma turbulence.

There is ample evidence for magnetic reconnection in the solar system, but it is a nontrivial task to visualize, to determine the proper approaches and frames to study, and in turn to elucidate the physical processes at work in reconnection regions from in-situ measurements of plasma particles and electromagnetic fields. Here an overview is given of a variety of single- and multi-spacecraft data analysis techniques that are key to revealing the context of in-situ observations of magnetic reconnection in space and for detecting and analyzing the diffusion regions where ions and/or electrons are demagnetized. We focus on recent advances in the era of the Magnetospheric Multiscale mission, which has made electron-scale, multi-point measurements of magnetic reconnection in and around Earth's magnetosphere.

We use the three-dimensional (3-D) global hybrid code ANGIE3D to simulate the interaction of four solar wind tangential discontinuities (TDs) observed by ARTEMIS P1 from 0740 UT to 0800 UT on 28 December 2019 with the bow shock, magnetosheath, and magnetosphere. We demonstrate how the four discontinuities produce foreshock transients, a magnetosheath cavity-like structure, and a brief magnetopause crossing observed by THEMIS and MMS spacecraft from 0800 UT to 0830 UT. THEMIS D observed entries into foreshock transients exhibiting low density, low magnetic field strength, and high temperature cores bounded by compressional regions with high densities and high magnetic field strengths. The MMS spacecraft observed cavities with strongly depressed magnetic field strengths and highly deflected velocity in the magnetosheath downstream from the foreshock. Dawnside THEMIS A magnetosheath observations indicate a brief magnetosphere entry exhibiting enhanced magnetic field strength, low density, and decreased and deflected velocity (sunward flow). The solar wind inputs into the 3-D hybrid simulations resemble those seen by ARTEMIS. We simulate the interaction of four oblique TDs with properties similar to those in the observation. We place virtual spacecraft at the locations where observations were made. The hybrid simulations predict similar characteristics of the foreshock transients, a magnetosheath cavity, and a magnetopause crossing with characteristics similar to those observed by the multi-spacecraft observations. The detailed and successful comparison of the interaction involving multiple TDs will be presented. We use the ANGIE3D hybrid codes to simulate the interaction of four solar wind discontinuities with the bow shock The characteristics of foreshock transients observed by THEMIS D match the predictions of the hybrid simulation well The simulation also predicts the plasma and magnetic field variations observed during a magnetosheath cavity and a brief magnetopause entry

Earth's magnetosheath is the region of shocked plasma that mediates coupling between the solar wind and magnetosphere. Magnetohydrodynamic (MHD) simulations predict electric current closure across the magnetosheath from the bow shock to the magnetopause. These currents provide a J x B force that diverts plasma flow along the flanks of the magnetosphere. Observations by the NASA Magnetospheric Multiscale (MMS) mission show that within the magnetosheath there are large amplitude, localized currents during periods of intense turbulence. We perform a statistical analysis of magnetic field data from the first 6 years (2015-2021) of the MMS mission during intervals when the satellites are on the dayside and generate statistical maps of electric current derived using the curlometer technique. We find that during the low magnetosonic Mach number regime (M-MS < 5), the predicted current closure pattern becomes apparent for northward and southward IMF orientations, but not dawnward or duskward. For M-MS > 5, results suggest that for all IMF orientations this large-scale current closure pattern is not apparent, even after separating out quasi-perpendicular (theta(bn) >= 45 degrees) and quasi-parallel (theta(bn) < 45 degrees) bow shock conditions. Instead, the magnetosheath is dominated by small-scale filamented current sheets that may be attributed to magnetosheath turbulence.

We survey 20 reconnection outflow events observed by Magnetospheric MultiScale in the low-β and high-Alfvén-speed regime of the Earth’s magnetotail to investigate the scaling of ion bulk heating produced by reconnection. The range of inflow Alfvén speeds (800–4000 km s−1) and inflow ion β (0.002–1) covered by this study is in a plasma regime that could be applicable to the solar corona and flare environments. We find that the observed ion heating increases with increasing inflow (upstream) Alfvén speed, V A, based on the reconnecting magnetic field and the upstream plasma density. However, ion heating does not increase linearly as a function of available magnetic energy per particle, m i V A 2 . Instead, the heating increases progressively less as m i V A 2 rises. This is in contrast to a previous study using the same data set, which found that electron heating in this high-Alfvén-speed and low-β regime scales linearly with m i V A 2 , with a scaling factor nearly identical to that found for the low-V A and high-β magnetopause. Consequently, the ion-to-electron heating ratio in reconnection exhausts decreases with increasing upstream V A, suggesting that the energy partition between ions and electrons in reconnection exhausts could be a function of the available magnetic energy per particle. Finally, we find that the observed difference in ion and electron heating scaling may be consistent with the predicted effects of a trapping potential in the exhaust, which enhances electron heating, but reduces ion heating.

We examine a Dipolarization Front (DF) event with an embedded electron diffusion region (EDR), observed by the Magnetospheric Multiscale (MMS) spacecraft on 08 September 2018 at 14:51:30 UT in the Earth's magnetotail by applying multi-scale multipoint analysis methods. In order to study the large-scale context of this DF, we use conjunction observations of the Cluster spacecraft together with MMS. A polynomial magnetic field reconstruction technique is applied to MMS data to characterize the embedded electron current sheet including its velocity and the X-line exhaust opening angle. Our results show that the MMS and Cluster spacecraft were located in two counter-rotating vortex flows, and such flows may distort a flux tube in a way that the local magnetic shear angle is increased and localized magnetic reconnection may be triggered. Using multi-point data from MMS we further show that the local normalized reconnection rate is in the range of R similar to 0.16 to 0.18. We find a highly asymmetric electron in- and outflow structure, consistent with previous simulations on strong guide-field reconnection events. This study shows that magnetic reconnection may not only take place at large-scale stable magnetopause or magnetotail current sheets but also in transient localized current sheets, produced as a consequence of the interaction between the fast Earthward flows and the Earth's dipole field. Magnetic Reconnection is a key energy conversion process, where magnetic energy is converted into kinetic energy of plasma particles. During this process the magnetic field topology changes and the plasma particles decouple from the magnetic field in the so-called diffusion region and get accelerated, forming a fast outflow jet. Over the last decades, hints arise that reconnection can take place at many different places in the magnetosphere and also very locally and intermittently. Fast plasma flows in the Magnetotail, moving toward the Earth, are assumed to be a consequence of magnetic reconnection, and are often accompanied by dipolar-shaped magnetic flux bundles, embedded into them. The leading edges of such flux bundles are called dipolarization fronts (DF). In this work, we investigate a DF event, which hosts a diffusion region. First, we study the large-scale characteristics of the DF, by utilizing data from both the Magnetospheric Multiscale (MMS) and the Cluster mission, that observe different regions of the event almost simultaneously. Second, we performed a 3D magnetic field reconstruction technique and compared the results to MMS data, to investigate the event on small scales. A thin current sheet inside a dipolarization front, embedded in a diverging flow is analyzed using a polynomial reconstruction techniqueTransient reconnection event is detected in a high magnetic shear region, where the magnetic field is deflected due to duskward fast plasma flowThe reconstructed current sheet has a guide field of similar to 1.8 the reconnecting component with normalized reconnection rate between 0.16 and 0.18

Abstract Using data from NASA's Magnetospheric Multiscale mission captured in a reconnection inflow on the magnetospheric side of Earth's dayside magnetopause, we find a region where the heat flux density gradient term balances the parallel compression term in the electron parallel temperature equation. Combining these observations with analysis of the generalized fluid equations indicates that such a behavior represents a quasi‐isothermal region, where cold magnetosheath beams that have transported across the magnetopause introduce non‐zero gradients in parallel heat flux density. This region should prevail near dayside reconnection X‐lines in inflows on the magnetospheric side due to the formation of mixed electron distributions and increased parallel temperatures that arise from three‐dimensional boundary dynamics.

Dayside magnetic reconnection allows for the transfer of the solar wind's energy into Earth's magnetosphere. This process takes place in electron diffusion regions (EDRs) embedded in ion diffusion regions (IDRs), which form in the magnetopause boundary's current sheet. A significant out-of-plane parallel current contribution in the diffusion regions was reported in Beedle et al. 2023. In order to understand the underlying structure of this parallel current, we compared EDR statistical results with a 2.5D Particle-In Cell (PIC) simulation. From this comparison, we identified out-of-plane parallel current signatures as defining features of the outer EDR and IDR. This significant out-of-plane parallel current indicates the interaction of the IDR and EDR systems, and provides implications for not only understanding energy dissipation in the diffusion regions, but also determining the location of the outer EDR.

The efficiency of energy conversion during magnetic reconnection is related to the reconnection rate. While the stable reconnection rate has been studied extensively, its growth between the time of reconnection onset and its peak has not been thoroughly discussed. We use a 2D particle-in-cell simulation to examine how the reconnection rate evolves during the growth process and how it relates to changes near the x-line. We identify three phases of growth: (a) slow quasi-linear growth, (b) rapid exponential growth, and (c) tapered growth followed by negative growth after the reconnection rate peaks. We associate phase 1 with the breaking of x-line uniformity by a localized density depletion that changes the in-plane electric field structure near the neutral line, followed by the expansion of the inflow region and the enhancement of inflow Poynting flux Sz associated with the out-of-plane electric field Ey in phase 2. We show how the Hall fields facilitate rapid growth in phase 2 by opening up the exhaust and relieving the electron-scale bottleneck to allow rapid energy transport across the separatrices. We find that in phase 3, the inflow of electromagnetic energy accumulates until the downstream electromagnetic energy density saturates toward the initial upstream asymptotic value. Finally, we examine how the electron outflow and the downstream ion populations interact in phase 3 and how each species exchanges energy with the local field structures in the exhaust. Growth of the reconnection rate characterized by three distinct phases Local density depletion initiates slow growth of reconnection rate and changes electrostatic structure Reconnection rate stabilizes as downstream magnetic energy density approaches its initial asymptotic value

Collisionless shocks are ubiquitous in space plasmas. The mechanisms responsible for energy conversion and particle acceleration in collisionless shocks remain elusive and central to many astrophysical problems. Here we propose to analyze and compare terms of the energy equation during Earth bow shock and magnetopause Electron Diffusion Region (EDR) crossings using the high-resolution, multi-spacecraft Magnetospheric MultiScale (MMS) mission. Direct derivations from the Vlasov-Maxwell equation provide the equation that describes the temporal evolution of the kinetic energy. In this study, we investigate, in a multifluid framework, the terms that quantify the acceleration or deceleration of ions and electrons, i.e., pressure-gradient force term, and the electromagnetic energy term. The former accounts for plasma acceleration/deceleration from a pressure-gradient, while the latter accounts for plasma acceleration/deceleration from an electric field. While global average balance between the terms is expected, deviations from zero are sources of accelerations or decelerations. We use in-situ observations from MMS to determine statistically the dominant terms responsible for electrons and ions acceleration in association with these two key phenomena: shocks and reconnection. In this ongoing work, we present the probability distribution functions of the relevant terms. We classify our results with respect to the Alfvènic Mach number and the plasma beta. We discuss the role of each term in accelerating, heating the plasma and producing or annihilating magnetic energy.

Understanding the motion of charged particles in the electromagnetic field in the inner magnetosphere is essential for space science and space weather. Charge accumulation can occur due to the dipole magnetic and convective electric fields in this region. However, until the recent Magnetospheric Multiscale (MMS) mission, there were few means to detect charge distribution in situ. We report unambiguous in situ observation of the spatial distribution of the excess charge density in the inner magnetosphere by the MMS mission. We find that a positive (negative) charge accumulates in the dusk (dawn) side inner magnetospheres, which is contrary to the long assumed overall quasi-neutrality of space plasma. These observations and results offer insight into magnetosphere–ionosphere coupling.

Supporting information for "Determining the orientation of a magnetic reconnection X line and implications for a 2D coordinate system", by Denton et al. Includes a copy of the paper and previous relevant papers, the simulation data used in the paper, and the reconstruction code used in the paper. See the readme files.

Fundamental processes in plasmas act to convert energies into different forms, e.g., electromagnetic, kinetic and thermal. Direct derivation from the Valsov-Maxwell equation yields sets of equations that describe the temporal evolution of the magnetic, kinetic and internal energies in either the monofluid or multifluid frameworks. In this work we focus on the main terms that affect the changes in the kinetic energy. These are pressure gradient-related terms and electromagnetic terms. The former account for plasma acceleration or deceleration from a pressure gradient, while the latter from an electric field. The overall balance between these terms is fundamental to ensure the conservation of energy and momentum. We use in-situ observations from the Magnetospheric MultiScale (MMS) mission to study the relationship between these terms. We perform a statistical analysis of those parameters in the context of magnetic reconnection by focusing on small-scale Electron Diffusion Regions and large-scale Flux Transfer Events. The analysis reveals a correlation between the two terms in the monofluid force balance, and in the ion force and energy balance. However, the expected relationship cannot be verified from electron measurements. Generally, the pressure gradient related terms are smaller than their electromagnetic counterparts. We perform an error analysis to quantify the expected underestimation of gradient values as a function of the spacecraft separation compared to the gradient scale. Our findings highlight that MMS is capable of capturing energy and force balance for the ion fluid, but that care should be taken for energy conversion terms based on electron pressure gradients.