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Recent multi-point measurements, in particular from the Magnetospheric Multiscale (MMS) spacecraft, have advanced the understanding of micro-scale aspects of magnetic reconnection. In addition, the MMS mission, as part of the Heliospheric System Observatory, combined with recent advances in global magnetospheric modeling, have furthered the understanding of meso- and global-scale structure and consequences of reconnection. Magnetic reconnection at the dayside magnetopause and in the magnetotail are the drivers of the global Dungey cycle, a classical picture of global magnetospheric circulation. Some recent advances in the global structure and consequences of reconnection that are addressed here include a detailed understanding of the location and steadiness of reconnection at the dayside magnetopause, the importance of multiple plasma sources in the global circulation, and reconnection consequences in the magnetotail. These advances notwithstanding, there are important questions about global reconnection that remain. These questions focus on how multiple reconnection and reconnection variability fit into and complicate the Dungey Cycle picture of global magnetospheric circulation. [ABSTRACT FROM AUTHOR]

Electromagnetic Ion Cyclotron (EMIC) waves mediate energy transfer from the solar wind to the magnetosphere, relativistic electron precipitation, or thermalization of the ring current population, to name a few. How these processes take place depends on the wave properties, such as the wavevector and polarization. However, inferring the wavevector from in‐situ measurements is problematic since one needs to disentangle spatial and time variations. Using 8 years of Magnetospheric Multiscale (MMS) mission observations in the dayside magnetosphere, we present an algorithm to detect proton‐band EMIC waves in the Earth's dayside magnetosphere, and find that they are present roughly 15% of the time. Their normalized frequency presents a dawn‐dusk asymmetry, with waves in the dawn flank magnetosphere having larger frequency than in the dusk, subsolar, and dawn near subsolar region. It is shown that the observations are unstable to the ion cyclotron instability. We obtain the wave polarization and wavevector by comparing Single Value Decomposition and Ampere methods. We observe that for most waves the perpendicular wavenumber (k⊥) is larger than the inverse of the proton gyroradius (ρi), that is, k⊥ρi > 1, while the parallel wavenumber is smaller than the inverse of the ion gyroradius, that is, k‖ρi < 1. Left‐hand polarized waves are associated with small wave normal angles (θBk < 30°), while linearly polarized waves are associated with large wave normal angles (θBk > 30°). This work constitutes, to our knowledge, the first attempt to statistically infer the full wavevector of proton‐band EMIC waves observed in the outer magnetosphere. Key Points: We conduct a statistical analysis of proton‐band Electromagnetic Ion Cyclotron (EMIC) waves in dayside magnetosphere using 8 years of Magnetospheric Multiscale data and measure full wavevectorsThe normalized frequency of EMIC waves presents a dawn‐dusk asymmetryThe perpendicular wavevector is, for most of the waves, larger than the inverse of proton gyroradius and ion inertial lengths [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a process that converts magnetic energy into kinetic energy, both bulk and thermal. We study the energy partition in magnetotail reconnection in the presence of cold ion populations of ionospheric origin using kinetic simulations. We compare two simulations with one or two ion populations, but same ion moments. The ion distribution in the simulation with cold ions therefore corresponds to a non‐Maxwellian distribution with a large tail. The global energy budget does not change in the two cases, but when focusing on sub‐populations, the hot ion population (i.e., the tail of the velocity distribution function) gains more energy than the cold ion population (i.e., the core of the distribution). Hot and cold ions also gain different percentages of bulk and thermal energy. Plain Language Summary: Magnetic reconnection is a process that converts magnetic energy into acceleration (bulk kinetic energy) and heating (thermal kinetic energy). In the magnetosphere, we often see a cold plasma population of ionospheric origin, on top of the hot magnetospheric plasma. We study the energy partition in magnetotail reconnection in the presence of those cold ions using simulations. We compare two simulations with and without cold ions, but same global parameters. We observe that the total energy partition is not significantly different between the simulations. But when focusing on the cold ion simulation, we see that hot ions gains more energy than cold ions and also have a larger bulk over thermal energy gain. Key Points: The energy budget in magnetic reconnection is not significantly affected by cold ion beams for constant inflow plasma global parametersThe hotter ion population gains more energy during magnetic reconnection than the colder oneMost of the energy gain of hot ions is in the form of internal energy, while the energy transferred to the cold ions is more balanced [ABSTRACT FROM AUTHOR]

A low-energy (cold) ion population of ionospheric origin is often present in the Earth's magnetic tail alongside with a thermal (hot) ion population. The presence of cold ions introduces small-scale effects in the dynamics of magnetic reconnection owing to their small gyroradius. Hall electric fields at the reconnection separatrices demagnetize and accelerate inflowing cold ions in the direction perpendicular to the local magnetic field. Once cold ions have passed through the accelerating layer, they enter the exhaust and continue to follow regular E × B drift motion. The overlap of cold ion trajectories produces a partial ring distribution function. A simple analytical model is proposed, pointing to the regular formation of these crescent-looking distribution functions, which we denote "crescent echoes." We performed two-dimensional particle-in-cell simulations to investigate these cold ion velocity space signatures in the reconnection exhaust. We carried out the simulations with various cold ion proportions relative to the hot ion component. In the reference run with very small, but non-negligible cold ion density, the distribution functions are very close to that from the analytical model. The reference run results are contrasted with the dynamics in the cold ion-dominated plasma in which ion–ion or lower-hybrid modes might develop. We conclude that an increased density of cold ions leads to blurring of the crescent echoes into a more thermal distribution due to wave activity development. [ABSTRACT FROM AUTHOR]

Santiago Redondo, Jorge Navarro-Dorado, Marta Ramajo, Úrsula Medina, Teresa TejerinaDepartment of Pharmacology, School of Medicine, Universidad Complutense, Madrid, SpainAbstract: Transforming growth factor β (TGF-β1) is a pleiotropic cytokine with many and complex effects in cell and tissue physiology. This is made possible by a very complex and interwoven signaling system, whose regulation continues to be the focus of a growing line of research. This complex regulation translates to a key role in cardiovascular physiology, hemostasis, and the blood–vessel interface. In accordance with this, the TGF-β1 pathway appears to be deregulated in related disorders, such as atherosclerotic vascular disease and myeloproliferative syndromes. It is expected that the growing amount of experimental and clinical research will yield medical advances in the applications of knowledge of the TGF-β1 pathway to diagnosis and therapeutics.Keywords: transforming growth factor beta, pathway, Smads, non-Smads, atherosclerosis, myeloproliferative syndromes

This article discusses a study that examines the association between maternal stress, placental gene expression and methylation, fetal cortisol metabolites in amniotic fluid, and birthweight in small-for-gestational-age (SGA) newborns. The study found that SGA pregnancies had higher levels of maternal stress and altered fetoplacental cortisol metabolism compared to pregnancies with adequate fetal growth. These findings provide insights into the pathophysiology of SGA and highlight the importance of strategies to reduce maternal stress. [Extracted from the article]

We have developed a new X-ray cone-beam tomograph for in vivo small-animal imaging using a flat panel detector (CMOS technology with a microcolumnar CsI scintillator plate) and a microfocus X-ray source. The geometrical configuration was designed to achieve a spatial resolution of about 12 lpmm with a field of view appropriate for laboratory rodents. In order to achieve high performance with regard to per-animal screening time and cost, the acquisition software takes advantage of the highest frame rate of the detector and performs on-the-fly corrections on the detector raw data. These corrections include geometrical misalignments, sensor non-uniformities, and defective elements. The resulting image is then converted to attenuation values. We measured detector modulation transfer function (MTF), detector stability, system resolution, quality of the reconstructed tomographic images and radiated dose. The system resolution was measured following the standard test method ASTM E1695-95. For image quality evaluation, we assessed signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) as a function of the radiated dose. Dose studies for different imaging protocols were performed by introducing TLD dosimeters in representative organs of euthanized laboratory rats. Noise figure, measured as standard deviation, was 50 HU for a dose of 10 cGy. Effective dose with standard research protocols is below 200 mGy, confirming that the system is appropriate for in vivo imaging. Maximum spatial resolution achieved was better than 50 micron. Our experimental results obtained with image quality phantoms as well as with in-vivo studies show that the proposed configuration based on a CMOS flat panel detector and a small micro-focus X-ray tube leads to a compact design that provides good image quality and low radiated dose, and it could be used as an add-on for existing PET or SPECT scanners.

We present a study of the Schumann resonance (SR) regular variations (March 2013–February 2017) using the ground‐based magnetometers from the Sierra Nevada station, Spain (37°02′N, 3°19′W). The study is based on the fitting parameters obtained by the Lorentzian fit, calculated for each 10‐min interval record, namely, peak amplitudes, peak frequencies, width of the resonances, and the power spectrum integral for the first three SR modes. We consider three time‐scales in the study: seasonal, monthly, and daily variations. The processed data collected by the Sierra Nevada station are also made public with this work. The general characteristics of the long‐term evolution of the SR are confirmed, but discrepancies appear that require further study comparing recent measurements from different stations. Signatures of the influences of the El Niño phenomenon and the solar cycle to SR have been found. Key Points: Long term analysis of the Schumann resonance (SR) records at Sierra Nevada, from March 2013 to February 2017The results obtained partially confirm the general aspects of the long‐term evolution of the SRs, but new aspects appearRecent results on the influence of the El Niño phenomenon and the solar cycle on the SRs are confirmed [ABSTRACT FROM AUTHOR]

In‐situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales of the system. To overcome this problem at least partially, multi‐point measurements can be used. There are several multi‐spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large‐scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (<0.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift. Key Points: Simultaneous observations of the equatorial subsolar magnetopause and dusk flank during time‐extended radial interplanetary magnetic fieldThe magnetosphere enlarges ∼0.7 RE in the subsolar region but <0.2 RE in the flank due to the reduced pressure exerted by the solar windSimultaneous reconnection evidence in the subsolar and flank regions more than 15 RE apart is observed during part of the encounter [ABSTRACT FROM AUTHOR]

Ionospheric ions (mainly H+, He+, and O+) escape from the ionosphere and populate the Earth's magnetosphere. Their thermal energies are usually low when they first escape the ionosphere, typically a few electron volt to tens of electron volt, but they are energized in their journey through the magnetosphere. The ionospheric population is variable, and it makes significant contributions to the magnetospheric mass density in key regions where magnetic reconnection is at work. Solar wind--magnetosphere coupling occurs primarily via magnetic reconnection, a key plasma process that enables transfer of mass and energy into the near-Earth space environment. Reconnection leads to the triggering of magnetospheric storms, auroras, energetic particle precipitation and a host of other magnetospheric phenomena. Several works in the last decades have attempted to statistically quantify the amount of ionospheric plasma supplied to the magnetosphere, including the two key regions where magnetic reconnection occurs: the dayside magnetopause and the magnetotail. Recent in situ observations by the Magnetospheric Multiscale spacecraft and associated modeling have advanced our current understanding of how ionospheric ions alter the magnetic reconnection process, including its onset and efficiency. This article compiles the current understanding of the ionospheric plasma supply to the magnetosphere. It reviews both the quantification of these sources and their effects on the process of magnetic reconnection. It also provides a global description of how the ionospheric ion contribution modifies the way the solar wind couples to the Earth's magnetosphere and how these ions modify the global dynamics of the near-Earth space environment. [ABSTRACT FROM AUTHOR]

This article presents 18 magnetic reconnection electron diffusion region (EDR) candidates found using a neural network algorithm with the Magnetospheric Multiscale Mission phase 1a data at the Earth's dayside magnetopause. These new candidates are compared to the 32 previously reported dayside EDRs listed in Webster et al. (2018), https://doi.org/10.1029/2018ja025245, which constitute the training database of our algorithm. One of the main parameters used is a scalar quantity called "MeanRL" which is based on the asymmetry of the electron velocity distribution function and better identifies electron agyrotropy in the plane perpendicular to the magnetic field. In the light of the new EDR candidates found, we discuss and analyze the sign of the energy dissipation during the reconnection process and the distinction between the inner and outer EDRs, with 40% of the candidates showing negative or oscillating dissipation. We also present in details one of the new identified EDR candidates. Key Points: We report 18 new electron diffusion region (EDR) candidates close to the Earth magnetopause in the Magnetospheric Multiscale Mission (MMS) phase 1a data using a neural networkThe algorithm makes use of a scalar quantity called "MeanRL" to identify the electron perpendicular agyrotropy typical of EDRs from MMS distribution functionsWe analyze and discuss the geometry of EDR based on energy dissipation signatures [ABSTRACT FROM AUTHOR]

We report observations of the ion dynamics inside an Alfvén branch wave that propagates near the reconnecting dayside magnetopause. The measured frequency, wave normal angle and polarization are consistent with the predictions of a dispersion solver. The magnetospheric plasma contains hot protons (keV), cold protons (eV), plus some heavy ions. While the cold protons follow the magnetic field fluctuations and remain frozen‐in, the hot protons are at the limit of magnetization. The cold protons exchange energy back and forth, adiabatically, with the wave fields. The cold proton velocity fluctuations contribute to balance the Hall term fluctuations in Ohm's law, and the wave E field has small ellipticity and right‐handed polarization. The dispersion solver indicates that increasing the cold proton density facilitates propagation and amplification of these waves at oblique angles, as for the observed wave. Plain Language Summary: The Earth's magnetosphere is a very dilute cloud of charged particles that are trapped in the Earth's magnetic field. This cloud is surrounded by the solar wind, another very dilute gas that flows supersonically throughout the solar system. These two plasmas can couple to each other via magnetic reconnection, a fundamental plasma process that occurs at the dayside region of the interface between the two plasmas. When reconnection occurs, large amounts of energy and particles enter the magnetosphere, driving the near Earth space dynamics and generating, for instance, aurorae. The magnetospheric plasma sources are the solar wind and the Earth's ionosphere. Multiple plasma populations can be found inside the Earth's magnetosphere, depending on the plasma origin and its time history, as well as the magnetospheric forcing of the solar wind. In this study, we show how the presence of multiple particle populations at the interface between the solar wind and the magnetosphere modifies the properties of the waves that propagate there. Waves are known to play a fundamental role in converting energy and heating these very dilute charged gas clouds. Key Points: In situ observation of different dynamics of cold (eV) and hot (keV) protons inside an electromagnetic ion cyclotron waveWave number estimation shows that cold protons behave as fluid while hot protons interact at kinetic scalesMagnetized cold protons modify the Ohm's law balance and favor propagation at a large wave normal angle [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron (EMIC) waves play important roles in particle loss processes in the magnetosphere. Determining the evolution of EMIC waves as they propagate and how this evolution affects wave-particle interactions requires accurate knowledge of the wave vector, k. We present a technique using the curl of the wave magnetic field to determine k observationally, enabled by the unique configuration and instrumentation of the Magnetospheric MultiScale (MMS) spacecraft. The wave curl analysis is demonstrated for synthetic arbitrary electromagnetic waves with varying properties typical of observed EMIC waves. The method is also applied to an EMIC wave interval observed by MMS on October 28, 2015. The derived wave properties and k from the wave curl analysis for the observed EMIC wave are compared with the Waves in Homogenous, Anisotropic, Multi-component Plasma (WHAMP) wave dispersion solution and with results from other single- and multi-spacecraft techniques. We find good agreement between k from the wave curl analysis, k determined from other observational techniques, and k determined from WHAMP. Additionally, the variation of k due to the time and frequency intervals used in the wave curl analysis is explored. This exploration demonstrates that the method is robust when applied to a wave containing at least 3-4 wave periods and over a rather wide frequency range encompassing the peak wave emission. These results provide confidence that we are able to directly determine the wave vector properties using this multi-spacecraft method implementation, enabling systematic studies of EMIC wave k properties with MMS. [ABSTRACT FROM AUTHOR]

Observations from the Magnetospheric Multiscale (MMS) mission are used to quantify the maximum effect of magnetospheric H+ and He+ on dayside magnetopause reconnection. A data base of current-sheet crossings from the first 2 years of the MMS mission is used to identify magnetopause crossings with the highest He+ concentrations. While all of these magnetopause crossings exhibit evidence of plasmaspheric plume material, only half of the crossings are directly associated with plasmaspheric plumes. The He+ density varies dramatically within the magnetosphere adjacent to the magnetopause, with density variations of an order of magnitude on timescales as short as 10 s, the time resolution of the composition instrument on MMS. Plasma wave observations are used to determine the total electron density, and composition measurements are used to determine the mass density in the magnetosheath and magnetosphere. These mass densities are then used with the magnetic field observations to determine the theoretical reduction in the reconnection rate at the magnetopause. The presence of high-density plasmaspheric plume material at the magnetopause causes transient reductions in the reconnection rate of up to -40%. Plain Language Summary As the solar wind propagates from the Sun to the Earth, it encounters two boundaries that limit its access to the near-Earth environment. The first is a bow shock that heats, slows, and deflects the solar wind. The second is the Earth's magnetopause, where the shocked solar wind is deflected around the Earth's magnetic field region called the magnetosphere. Magnetic reconnection at the magnetopause creates an interconnection between the magnetic field of the shocked solar wind and the Earth's magnetic field. The rate at which these magnetic fields interconnect, the reconnection rate, depends on the amount of plasma (ions and electrons) on either side of the magnetopause. This research uses observations from the Magnetospheric Multiscale mission to look at this rate for times when there is substantial plasma on the magnetospheric side of the magnetopause. These instances are rare; however, when they do occur, they reduce the reconnection rate by a substantial amount (up to 40%). [ABSTRACT FROM AUTHOR]

Energetic neutral atoms (ENAs) created by charge‐exchange of ions with the Earth's hydrogen exosphere near the subsolar magnetopause yield information on the distribution of plasma in the outer magnetosphere and magnetosheath. ENA observations from the Interstellar Boundary Explorer (IBEX) are used to image magnetosheath plasma and, for the first time, low‐energy magnetospheric plasma near the magnetopause. These images show that magnetosheath plasma is distributed fairly evenly near the subsolar magnetopause; however, low‐energy magnetospheric plasma is not distributed evenly in the outer magnetosphere. Simultaneous images and in situ observations from the Magnetospheric Multiscale (MMS) spacecraft from November 2015 (during the solar cycle declining phase) are used to derive the exospheric density. The ~11–17 cm−3 density at 10 RE is similar to that obtained previously for solar minimum. Thus, these combined results indicate that the exospheric density 10 RE from the Earth may have a weak dependence on solar cycle. Key Points: ENA cameras image both magnetosheath and magnetospheric plasmas in the vicinity of the subsolar magnetopauseMagnetospheric plasma is not distributed evenly across the dayside near the magnetopauseThe exospheric hydrogen density near the magnetopause may have a weak dependence on solar F10.7 [ABSTRACT FROM AUTHOR]

Magnetopause Kelvin‐Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small‐scale mechanisms. Vortex‐induced reconnection (VIR) was predicted in simulations and recently observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations, but detailed observations were still lacking. Here we report MMS observations of an FTE‐type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterized by (1) bipolar magnetic BY variation with enhanced core field (BZ) and (2) enhanced total pressure with dominant magnetic pressure. The cross‐section size of the FTE is found to be consistent with vortex‐induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY); electron parallel heating, ion, and electron density enhancements; and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE‐type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019s). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves. Key Points: We present an MMS observation of a Flux Transfer Event‐type structure during a KH event on the dawn flank magnetopause beyond the terminatorIts characteristics are consistent with a structure produced from multiple vortex‐induced reconnection X‐linesReconnection signatures are found at the central current sheet while properties on either side indicate two flux tubes that interlace [ABSTRACT FROM AUTHOR]

Flux transfer events (FTEs) are transient phenomena frequently observed at the Earth's magnetopause. Their usual interpretation is a flux rope moving away from the reconnection region. However, the Magnetospheric Multiscale Mission revealed that magnetic reconnection sometimes occurs inside these structures, questioning their flux rope configuration. Here we investigate 229 FTE‐type structures and find reconnection signatures inside 19% of them. We analyze their large‐scale magnetic topology using electron heat flux and find that it is significantly different across the FTE reconnecting current sheets, demonstrating that they are constituted of two magnetically disconnected structures. We also find that the interplanetary magnetic field (IMF) associated with reconnecting FTEs presents a strong By component. We discuss several formation mechanisms to explain these observations. In particular, the maximum magnetic shear model predicts that for large IMF By, two spatially distinct X lines coexist at the magnetopause. They can generate separate magnetic flux tubes that may become interlaced. Plain Language Summary: The solar wind and the Earth's magnetosphere are two gigantic magnetic structures that collide constantly over our heads, in the near‐space environment. At the boundary of their interaction (the magnetopause), the fundamental process of magnetic reconnection can occur. It is there that dynamic magnetic structures called "flux transfer events" are formed. They travel fast along the magnetopause and transport a lot of energy, from the solar wind into the magnetosphere. These structures are yet not well understood, as underlined by the recent observations made by the Magnetospheric Multiscale Mission (MMS), launched in 2015 by National Aeronautics and Space Administration. The four‐spacecraft mission, specifically designed to study the physics happening at the magnetopause, is capable of measuring right into these magnetic structures, collecting data on their particles and magnetic field properties. When analyzing MMS data, we found that 19% of the flux transfer events were not constituted of one, but two structures with very different properties. These dual magnetic structures tend to appear when the solar wind's magnetic field is oriented mainly toward the east or the west. From these observations and based on existing models of the magnetopause, we propose a scenario that allows such dual structures to form as interlaced magnetic tubes. Key Points: Nineteen percent of FTE‐type structures observed by MMS during Phases 1A and 1B present signatures of magnetic reconnection in their coreThey seem to be formed by two magnetically disconnected interlaced flux tubes and are typically observed for large IMF BySeveral formation models are discussed, including a bifurcated X line scenario that results from the maximum shear angle model [ABSTRACT FROM AUTHOR]

During periods of strong magnetic activity, cold dense plasma from the plasmasphere typically forms a plume extending toward the dayside magnetopause, eventually reaching it. In this work, we present a large‐scale two‐dimensional fully kinetic particle‐in‐cell simulation of a reconnecting magnetopause hit by a propagating plasmaspheric plume. The simulation is designed so that it undergoes four distinct phases: initial unsteady state, steady state prior to plume arrival at the magnetospause, plume interaction, and steady state once the plume is well engulfed in the reconnection site. We show the evolution of the magnetopause's dynamics subjected to the modification of the inflowing plasma. Our main result is that the change in the plasma temperature (cold protons in the plume) has no effects on the magnetic reconnection rate, which on average depends only on the inflowing magnetic field and total ion density, before, during, and after the impact. Key Points: We run particle‐in‐cell simulation of asymmetric magnetic reconnection including the impact of a cold plasmaspheric plumeThe impact of the plume reduces the reconnection rate following Magnetohydrodynamics scaling laws due to mass loading onlyThe cold temperature of the plume does not influence the reconnection rate [ABSTRACT FROM AUTHOR]

The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm‐3 and the H+ density is <1.5 cm‐3, then O+ dominates the magnetospheric ion mass density by more than a factor of 2. A survey is conducted of such O+‐rich warm plasma cloak intervals and their effect on reconnection at the Earth's magnetopause. The survey uses data from the Magnetospheric Multiscale mission (MMS) and the results are compared and combined with a previous survey of the warm plasma cloak. Overall, the warm plasma cloak and the O+‐rich warm plasma cloak reduce the magnetopause reconnection rate by >20% due to mass‐loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions. Key Points: The magnetospheric warm plasma cloak is O+‐rich during geomagnetically active timesThe warm plasma cloak reduces the magnetic reconnection rate at the magnetopause ~2‐4% of the timeDuring geomagnetic storms, the O+‐rich warm plasma cloak reduces the reconnection rate by >20% sometime during 25% of the storms [ABSTRACT FROM AUTHOR]

Cold plasma (up to few tens of electron volts) of ionospheric origin is present most of the time, in most of the regions of the Earth's magnetosphere. However, characterizing it using in situ measurements is difficult, owing to spacecraft electrostatic charging, as often this charging is at levels comparable to or even higher than the equivalent energy of the cold plasma. To overcome this difficulty, active potential control devices are usually placed on spacecraft that artificially reduce spacecraft charging. The electrostatic potential structure around the spacecraft is often assumed to be spherically symmetric, and corrections are applied to the measured particle distribution functions. In this work, we show that large deviations from the spherical model are present, owing to the presence of long electric field booms. We show examples using Magnetospheric MultiScale spacecraft measurements of the electrostatic potential structure and its effect on the measurement of cold ion beams. Overall, we find that particle detectors underestimate the cold ion density under certain conditions, even when their bulk kinetic energy exceeds the equivalent spacecraft potential energy and the ion beam reaches the spacecraft. Active potential control helps in reducing this unwanted effect, but we show one event with large cold ion density (∼10 cm−3) where particle detectors provide density estimates a factor of 3–5 below the density estimated from the plasma frequency. Understanding these wake effects indirectly constrains some properties of the magnetospheric cold ion component, such as their drift energy, direction, and temperature. Plain Language Summary: The near‐Earth space environment is filled with plasma, that is, ionized gas that interacts with electromagnetic fields. Owing to its relative accessibility, it constitutes an invaluable laboratory for understanding how plasmas behave in nature. Many spacecraft missions have been launched with the purpose of studying space plasmas since the 1960s, when the space era began. They carry in situ instrumentation capable of measuring the properties of electric and magnetic fields, as well as the properties of ions and electrons. One problem these missions encounter is that the spacecraft produce their own electromagnetic fields that locally interact with the plasma and modify their properties. In this work, we quantify the effects of electric field booms mounted on spacecraft, which have length scales much larger than the spacecraft itself. The electromagnetic properties of these spacecraft booms strongly affect the detection and characterization of cold plasma, that is, low‐temperature plasma. Cold plasma in the near‐Earth space environment originates in the ionosphere, populates the whole magnetosphere, and constitutes the most abundant magnetospheric population. Key Points: The modeled MMS spacecraft electrostatic potential distribution deviates from spherical because of the electric field boomsMeasurements by particle detectors in the magnetosphere are strongly affected and biased by the complex potential structureCold ion beam properties are constrained by characterizing the ion wake and using a combination of particle and electric field measurements [ABSTRACT FROM AUTHOR]

As spacecraft does not have an independent method to conduct charge to ground, it naturally accumulates charge due to interactions with the ambient plasma and surface emission. This charge produces an electric field surrounding the spacecraft, which takes the form of a plasma sheath. Charged particles traveling through this sheath are altered in both energy and direction, thus affecting derived scientific quantities. While this effect has been known since the advent of space based particle instruments, this work represents the first time that an in situ characterization study of this effect has been possible. The Fast Plasma Investigation, of the Magnetospheric Multiscale mission, obtains near simultaneous measurements of phase space, via particle counts from 512 look directions and 32 energies. These new data allow the relative effects of the plasma sheath to be explored at a high time and spatial resolution. This work presents a method by which these measurements are used to study a ground model that traces the migration of particles through the sheath and estimates the error in measured velocity. This approach, performed statistically, leads to an estimation of uncertainty in particle count distributions for a given location in phase space and characterization of the redistribution of counts within a skymap due to sheath effects. [ABSTRACT FROM AUTHOR]

Traditionally, dipolarization front (DF) is a discontinuity at the leading edge of the high‐speed plasma jets, separating hot tenuous plasma from the denser ambient plasma. The particles behind the DF are usually hot population resulting from various heating and acceleration processes therein. Here, using Magnetospheric Multiscale (MMS) observations, we report that cold ions of ionospheric origin can be found behind the DFs. These cold ions move along the reconnected magnetic field lines directly from lobe during substorm, forming counter‐streaming cold ion flows behind the DFs. We find that cold ionospheric ions, as an additional population behind the DF, could increase ion density by ~50%. This indicates that the cold ions can change the gradients in the plasma density, such as the density‐driven instabilities near the DFs, and further affect the DF dynamics. Plain Language Summary: Dipolarization front (DF), a structure at the leading edge of the high‐speed plasma jets in the Earth's magnetotail, is responsible for the particles' acceleration, energy conversion, and magnetic flux transport during substorms. Typically, the ions behind the DFs are hot population from reconnection sites. Using data from the Magnetospheric Multiscale mission, we report the existence of ionospheric cold ions behind the DFs and propose a model to explain the appearance of these cold ions. Also, we investigate the effects of these ions on the DF dynamics, which is significant for studying the particles and energy transport in the magnetotail. Key Points: For the first time, we observe ionospheric cold ions behind DFsWe propose a model to explain the appearance of these cold ionsWe investigate the effects of these cold ions on the DF dynamics [ABSTRACT FROM AUTHOR]

When the interplanetary magnetic field is northward for a period of time, O+ from the high‐latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual‐lobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+‐rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high‐shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high‐latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause. Key Points: During sustained periods of northward IMF, O+ from the dayside high‐latitude ionosphere mass loads the boundary layer adjacent to the magnetopauseFor the example shown, this mass loading is substantial and does have an effect on reconnection at the magnetopause when the IMF turns southwardThis mass loading causes a transient reduction in the reconnection rate but does not suppress reconnection at the magnetopause [ABSTRACT FROM AUTHOR]

At the Earth's magnetopause, a low‐energy ion population of ionospheric origin is commonly observed at the magnetospheric side. In this work we use a 2‐D fully kinetic simulation to identify several original signatures related to the dynamics of cold ions involved in magnetic reconnection at the asymmetric dayside magnetopause. We identify several original signatures of the cold ions dynamics driven by the development of magnetic reconnection at the asymmetric dayside magnetopause. We find that cold ions tend to rarefy in the diffusion region, while their density is enhanced as a result of compression along magnetospheric separatrices. We also observe the formation of crescent‐shaped cold ion distribution functions along the separatrices in the near‐exhaust region, and we present an analytical model to explain this signature. Finally, we give evidence of a localized parallel heating of cold ions. These signatures should be detected with the magnetospheric multiscale mission high‐resolution observations. Key Points: We make PIC simulations of asymmetric magnetic reconnection including both hot and cold magnetospheric ion populationsWe study cold ions' specific signatures along magnetospheric separatricesWe develop a theoretical model for the crescent‐shaped distribution functions of cold ions observed along the separatrices separatrix [ABSTRACT FROM AUTHOR]

We report MMS observations of the ion‐scale flux transfer events (FTEs) that may involve two main X lines and tearing instability between the two X lines. The four spacecraft detected multiple isolated regions with enhanced magnetic field strength and bipolar Bn signatures normal to the nominal magnetopause, indicating FTEs. The currents within the FTEs flow mostly parallel to B, and the magnetic tension force is balanced by the total pressure gradient force. During these events, the plasma bulk flow velocity was directed southward. Detailed analysis of the magnetic and electric field and plasma moments variations suggests that the FTEs were initially embedded within the exhaust region north of an X line but were later located southward/downstream of a subsequent X line. The cross sections of the individual FTEs are in the range of ~2.5–6.8 ion inertial lengths. The observations suggest the formation of multiple secondary FTEs. The presence of an X line in the exhaust region southward of a second X line results from the southward drift of an old X line and the reformation of a new X line. The current layer between the two X lines is unstable to the tearing instability, generating multiple ion‐scale flux‐rope‐type secondary islands. Key Points: MMS observation of ion‐scale flux ropes in the reconnection outflow regionThe initial X line is embedded in the exhaust region downstream of a second X lineFlux transfer events (FTE) are formed between the two X lines due to tearing instability [ABSTRACT FROM AUTHOR]

Abstract: Turbulence in the Earth's magnetosheath at ion kinetic scales is investigated with the magnetospheric multiscale spacecraft. Several possibilities in the wave paradigm have been invoked to explain plasma turbulence at ion kinetic scales such as kinetic Alfvén, slow, or magnetosonic waves. To differentiate between these different plasma waves is a challenging task, especially since some waves, in particular, kinetic slow waves and kinetic Alfvén waves, share some properties making the possibility to distinguishing between them very difficult. Using the excellent time resolution data set provided from both the fluxgate magnetometer and the Fast Plasma Instrument, the ratio of trace velocity fluctuations to the magnetic fluctuations (in Alfvén units), which is termed the Alfvén ratio, can be calculated down to ion kinetic scales. Comparison of the measured Alfvén ratio is performed with respect to the expectation from two‐fluid magnetohydrodynamic theory for the kinetic slow wave and kinetic Alfvén wave. Moreover, the plasma data also allow normalized fluctuation amplitudes of density and magnetic field to be compared differentiating between magnetosonic‐like and kinetic Alfvén‐like turbulence. Using these two different ratios, we can rule out that the fluctuations at ion scales are dominated by magnetosonic‐like fluctuations or kinetic slow‐like fluctuations and show that they are consistent with kinetic Alfvén‐like fluctuations. This suggests that in the wave paradigm, heating in the direction of the parallel magnetic field is predominantly by the Landau damping of the kinetic Alfvén wave. [ABSTRACT FROM AUTHOR]

Abstract: We identify the electron diffusion region (EDR) of a guide field dayside reconnection site encountered by the Magnetospheric Multiscale (MMS) mission and estimate the terms in generalized Ohm's law that controlled energy conversion near the X‐point. MMS crossed the moderate‐shear (∼130°) magnetopause southward of the exact X‐point. MMS likely entered the magnetopause far from the X‐point, outside the EDR, as the size of the reconnection layer was less than but comparable to the magnetosheath proton gyroradius, and also as anisotropic gyrotropic “outflow” crescent electron distributions were observed. MMS then approached the X‐point, where all four spacecraft simultaneously observed signatures of the EDR, for example, an intense out‐of‐plane electron current, moderate electron agyrotropy, intense electron anisotropy, nonideal electric fields, and nonideal energy conversion. We find that the electric field associated with the nonideal energy conversion is (a) well described by the sum of the electron inertial and pressure divergence terms in generalized Ohms law though (b) the pressure divergence term dominates the inertial term by roughly a factor of 5:1, (c) both the gyrotropic and agyrotropic pressure forces contribute to energy conversion at the X‐point, and (d) both out‐of‐the‐reconnection‐plane gradients (∂/∂M) and in‐plane (∂/∂L,N) in the pressure tensor contribute to energy conversion near the X‐point. This indicates that this EDR had some electron‐scale structure in the out‐of‐plane direction during the time when (and at the location where) the reconnection site was observed. [ABSTRACT FROM AUTHOR]

Magnetosheath plasma usually determines properties of asymmetric magnetic reconnection at the subsolar region of Earth's magnetopause. However, cold plasma that originated from the ionosphere can also reach the magnetopause and modify the kinetic physics of asymmetric reconnection. We present a magnetopause crossing with high-density (10-60 cm−3) cold ions and ongoing reconnection from the observation of the Magnetospheric Multiscale (MMS) spacecraft. The magnetopause crossing is estimated to be 300 ion inertial lengths south of the X line. Two distinct ion populations are observed on the magnetosheath edge of the ion jet. One population with high parallel velocities (200-300 km/s) is identified to be cold ion beams, and the other population is the magnetosheath ions. In the deHoffman-Teller frame, the field-aligned magnetosheath ions are Alfvénic and move toward the jet region, while the field-aligned cold ion beams move toward the magnetosheath boundary layer, with much lower speeds. These cold ion beams are suggested to be from the cold ions entering the jet close to the X line. This is the first observation of the cold ionospheric ions in the reconnection outflow region, including the reconnection jet and the magnetosheath boundary layer. [ABSTRACT FROM AUTHOR]