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Waves around the lower hybrid frequency are frequently observed at Earth's magnetopause and readily reach very large amplitudes. Determining the properties of lower hybrid waves is crucial because they are thought to contribute to electron and ion heating, cross‐field particle diffusion, anomalous resistivity, and energy transfer between electrons and ions. All these processes could play an important role in magnetic reconnection at the magnetopause and the evolution of the boundary layer. In this paper, the properties of lower hybrid waves at Earth's magnetopause are investigated using the Magnetospheric Multiscale mission. For the first time, the properties of the waves are investigated using fields and direct particle measurements. The highest‐resolution electron moments resolve the velocity and density fluctuations of lower hybrid waves, confirming that electrons remain approximately frozen in at lower hybrid wave frequencies. Using fields and particle moments, the dispersion relation is constructed and the wave‐normal angle is estimated to be close to 90° to the background magnetic field. The waves are shown to have a finite parallel wave vector, suggesting that they can interact with parallel propagating electrons. The observed wave properties are shown to agree with theoretical predictions, the previously used single‐spacecraft method, and four‐spacecraft timing analyses. These results show that single‐spacecraft methods can accurately determine lower hybrid wave properties. The velocity and density fluctuations of magnetopause lower hybrid waves are resolved, showing that electrons are approximately frozen inLower hybrid wave dispersion relation and wave‐normal angle are computed from fields and particle measurementsSingle‐ and multi‐spacecraft methods yield consistent lower hybrid wave properties, confirming the accuracy of single‐spacecraft methods

We report Magnetospheric Multiscale observations of electron pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular electron bulk velocity from E× Bdrift in the interval where the out‐of‐plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out‐of‐plane current is transitioning to in‐plane current, the electron momentum equation is not satisfied at 7.5 ms resolution. Diamagnetic drift explains out‐of‐plane current in regions of deviation from frozen‐in fluxPerpendicular crescents exist in regions where electrons are diamagnetically driftingNew technique for extracting 7.5 ms electron moments produces reliable data

Electron heating and mixing during asymmetric reconnection are studied with a 3‐D kinetic simulation that matches plasma parameters from Magnetospheric Multiscale (MMS) spacecraft observations of a magnetopause diffusion region. The mixing and heating are strongly enhanced across the magnetospheric separatrix compared to a 2‐D simulation. The transport of particles across the separatrix in 3‐D is attributed to lower hybrid drift turbulence excited at the steep density gradient near the magnetopause. In the 3‐D simulation (and not the 2‐D simulation), the electron temperature parallel to the magnetic field within the mixing layer is significantly higher than its upstream value in agreement with the MMS observations. A fully kinetic 3‐D simulation resolves electron mixing and heating at a magnetopause reconnection site matching MMS observationsLower hybrid range drift turbulence mixes plasma across the magnetospheric separatrixStrong parallel electron heating near the current layer, as observed by MMS, is reproduced only in 3‐D

Models for collisionless magnetic reconnection in near‐Earth space are distinctly characterized as 2D or 3D. In 2D kinetic models, the frozen‐in law for the electron fluid is usually broken by laminar dynamics involving structures set by the electron orbit size, while in 3D models the width of the electron diffusion region is broadened by turbulent effects. We present an analysis of in situ spacecraft observations from the Earth's magnetotail of a fortuitous encounter with an active reconnection region, mapping the observations onto a 2D spatial domain. While the event likely was perturbed by low‐frequency 3D dynamics, the structure of the electron diffusion region remains consistent with results from a 2D kinetic simulation. As such, the event represents a unique validation of 2D kinetic, and laminar reconnection models. Magnetic reconnection is a fundamental process that occurs in the near‐Earth space environment with implications for the safety and longevity of space‐borne electronics in which magnetic field lines rearrange and release energy. To understand whether reconnection is better described as occurring in a 2D‐plane without variation in the third direction versus 3D with variation in all directions, we analyze spacecraft data from the night‐side of Earth's magnetic field. We conclude for the considered event that the innermost region, where the field lines reconnect, remains consistent with results from a 2D simulation. The fluctuating measurements are consistent with a 2D reconnecting geometry, permitting a detailed spacecraft trajectory to be determinedThe Magnetospheric Multiscale Mission data is projected onto a 2D spatial domain, revealing the fine‐scale structure of the electron diffusion region (EDR)The EDR includes profiles with strong gradients in fields and flows, consistent with those observed in a matched 2D kinetic simulation The fluctuating measurements are consistent with a 2D reconnecting geometry, permitting a detailed spacecraft trajectory to be determined The Magnetospheric Multiscale Mission data is projected onto a 2D spatial domain, revealing the fine‐scale structure of the electron diffusion region (EDR) The EDR includes profiles with strong gradients in fields and flows, consistent with those observed in a matched 2D kinetic simulation

Collective Thomson scattering (CTS) has been proposed as a viable diagnostic for characterizing fusion born α-distributions in ITER. However, the velocities of the planned 1 MeV deuterium heating beam ions in ITER are similar to that of fusion born α-particles and may therefore mask the measurements of the fusion products. We apply a new technique for calculating the orbit averaged source, 〈S〉, of beam ions for various ITER scenarios. With the known 〈S〉 Fokker–Planck modelling is applied to characterize the beam ions during the slowing down process. Theoretical CTS signals for both beam ions and the α-particles are calculated. Our investigations show that the CTS measurements of α-particles will not be masked by the presence of the beam ions in H-mode plasmas. In lower density reversed shear plasmas, only a part of the CTS α-particle spectrum will be perturbed.

Methods are developed for evaluation of the drift orbit averaged particle source, 〈S〉, in realistic neutral beam injection scenarios. Finite Larmor radius (FLR) and finite orbit width effects are included providing an accurate treatment of beam injection geometries in both standard and spherical tokamaks. With the knowledge of 〈S〉 the full beam distribution is readily obtained using well-known Fokker–Planck modelling schemes in constant of motion variables. For the considered ITER beam injection scenarios the analysis provides distributions which are in good agreement with equivalent distributions calculated by the TRANSP analysis code. The inclusion of FLR effects is important for fusion devices with relatively small values of the magnetic field; this is illustrated by considering the beam injection scenario of a spherical tokamak.

Collective Thomson scattering (CTS) has been proposed as a viable diagnostic for characterizing fusion born α-distributions in ITER. However, the velocities of the planned 1 MeV deuterium heating beam ions in ITER are similar to that of fusion born α-particles and may therefore mask the measurements of the fusion products. We apply a new technique for calculating the orbit averaged source, 〈S〉, of beam ions for various ITER scenarios. With the known 〈S〉 Fokker–Planck modelling is applied to characterize the beam ions during the slowing down process. Theoretical CTS signals for both beam ions and the α-particles are calculated. Our investigations show that the CTS measurements of α-particles will not be masked by the presence of the beam ions in H-mode plasmas. In lower density reversed shear plasmas, only a part of the CTS α-particle spectrum will be perturbed.

Magnetic reconnection is a fundamental process in collisionless space plasma environment, and plasma waves relevant to the kinetic interactions can have a significant impact on the multiscale behavior of reconnection. Here, we present Magnetospheric Multiscale (MMS) observations during an encounter of an X line of symmetric magnetic reconnection in the magnetotail. The X line is characterized by reversals of ion and electron jets and electromagnetic fields, agyrotropic electron velocity distribution functions (VDFs), and an electron‐scale current sheet. MMS observe large‐amplitude nonlinear upper‐hybrid (UH) waves on both sides of the neutral line, and the wave amplitudes have highly localized distribution along the normal direction. The inbound meandering electrons drive the UH waves, releasing the free energy stored from the reconnection electric field along the meandering trajectories. The interaction between the meandering electrons and the UH waves may modify the balance of the reconnection electric field around the X line. The electron‐scale kinetic physics in the electron diffusion region (EDR) controls how magnetic field lines break and reconnect. Electron crescent, an indicator of EDR, can drive high‐frequency electrostatic waves around EDR. For the first time, the upper‐hybrid (UH) waves are observed on both sides of the X line and we show the direct association between the UH waves and the reconnection electric field. The strong wave‐electron interaction can change the electron‐scale dynamics and may modify the reconnection electric field. This study demonstrates that the UH waves may play an important role in controlling the reconnection rate. Large amplitude nonlinear upper‐hybrid (UH) waves are observed on both inflow sides of an X lineThe UH waves are driven by the inbound meandering electronsThe UH waves may dissipate a significant part of the meandering electron energy gained from the reconnection electric field Large amplitude nonlinear upper‐hybrid (UH) waves are observed on both inflow sides of an X line The UH waves are driven by the inbound meandering electrons The UH waves may dissipate a significant part of the meandering electron energy gained from the reconnection electric field

Previous studies have concluded that the Hall magnetic field structures generated during magnetic reconnection are carried away by kinetic Alfvén waves. Here, we apply a kinetic simulation with an ion/electron mass ratio closer to its natural value and find that open boundary conditions and much reduced damping rates permit the shear Alfvén waves (SAWs) to become the main carrier of wave energy. For magnetotail reconnection, these SAWs provide efficient transport of wave energy, enhancing the energy input for the Aurora Borealis by orders of magnitude above previous estimates. Magnetic reconnection is the process of breaking and rearranging of the magnetic field in a plasma. It typically occurs very rapidly and permits the release of built‐up magnetic stress into plasma flows and heating. It is this energy conversion which is thought to be a critical mechanism for particle energization throughout space. A key unanswered question regards how the released energy and associated signatures propagate away from the reconnection site. In this paper, we analyze fully kinetic simulation results of magnetic reconnection to study how the waves driven by the reconnection process carry the reconnection signature, that is, out‐of‐plane magnetic field, and therefore transport energy to far away distances. We observe the reconnection launches both long and short‐wavelength Alfvén waves. However, it is the long wavelength Alfvén waves that survive and propagate far away from the reconnection site carrying enough energy to be important to the auroral phenomena at the poles. The quadrupole Hall structure of reconnection propagate away as kinetic Alfvén waves and shear Alfvén waves (SAWs)A large numerical domain and open boundary conditions are required for exciting strong SAWs by reconnectionPoynting flux associated with these SAWs is 400 above estimates in previous work and may cause the auroral phenomena The quadrupole Hall structure of reconnection propagate away as kinetic Alfvén waves and shear Alfvén waves (SAWs) A large numerical domain and open boundary conditions are required for exciting strong SAWs by reconnection Poynting flux associated with these SAWs is 400 above estimates in previous work and may cause the auroral phenomena

During magnetic reconnection in collisionless space plasma, the electron fluid decouples from the magnetic field within narrow current layers, and theoretical models for this process can be distinguished in terms of their predicted current layer widths. From theory, the off‐diagonal stress in the electron pressure tensor is related to the thermal noncircular orbit motion of electrons around the magnetic field lines. This stress becomes significant when the width of the reconnecting current layer approaches the small characteristic length scale of the electron motion. To aid in situ spacecraft and numerical investigations of reconnection, the structure of the electron diffusion region is here investigated using the Terrestrial Reconnection Experiment. In agreement with the closely matched kinetic simulations, laboratory observations reveal the presence of electron‐scale current layer widths. Although the layers are modulated by a current‐driven instability, three‐dimensional simulations demonstrate that it is the off‐diagonal stress that is responsible for breaking the frozen‐in condition of the electron fluid. “Space weather” describes the conditions of the plasma surrounding the Earth, which can have a severe impact on the functionality of spacecraft as well as the health of human space travelers. Space weather and the dynamics of space plasmas in general are closely linked to the structure and topology of the magnetic fields permeating our solar system. By a process called magnetic reconnection, magnetic field lines can rapidly and suddenly break and reconfigure their connectivity, allowing for an explosive release of magnetic energy. This phenomenon is at the origin of explosive events such as solar flares and is the driver of magnetic storms in the Earth's magnetosphere powering the Auroras. We present new laboratory observations of this near‐Earth reconnection process recreated in the Terrestrial Reconnection Experiment. The experiment provides detailed measurements of the width of the region where the magnetic field lines break, the electron diffusion region (EDR). Consistent with supercomputer simulations of reconnection, the width of the EDR is measured to be set by the fine spatial scale of the electron orbit motions. As such, the observations provide renewed evidence that the reconnection process is mediated by forces of thermal stress related to the electron motion within the reconnection region. The structure of the electron diffusion region is important to reconnection in space plasmaThe widths of laboratory electron reconnection layers match those of kinetic simulationsKinetic simulations show that the electron pressure tensor breaks the electron frozen flux condition The structure of the electron diffusion region is important to reconnection in space plasma The widths of laboratory electron reconnection layers match those of kinetic simulations Kinetic simulations show that the electron pressure tensor breaks the electron frozen flux condition

Summary from earth-current observations made at Mogadiscio the lunar-diurnal variation has been derived for the northward component, and by means of a special method lunar variations during daylight hours and night hours have been determined separately. The results have been compared with corresponding results from other observatories.

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We analyze data returned by the Magnetospheric Multiscale mission (MMS) constellation during a rapid (∼1.5 s) traversal of a flapping and reconnecting current sheet (CS) in the near‐Earth magnetotail (X ∼−20 RE). The CS was highly tilted, with its normal pointing strongly duskward. Its extreme thinness was confirmed by a curvature analysis of the magnetic field lines. The event was associated with a guide field of 8% of the reconnecting components. From the pitch angle distributions of low‐energy electrons we infer a crossing earthward of the X‐line. Traveling practically normal to the CS, MMS encountered an ion diffusion region (IDR) in which was embedded an electron diffusion region (EDR). IDR signatures included breaking of the ion frozen‐in condition in the presence of Hall Band Efields. EDR signatures included a strong out‐of‐plane current associated with a superAlfvénic electron jet, positive energy transfer, and a temperature anisotropy (Te∥> Te⊥) which disappeared at the field reversal. Derived scale sizes normal to the CS are: ∼6.9 de(EDR) and ∼0.4 di(IDR; 40 and 100 km). We estimate the average dimensionless reconnection rate as 0.077 ± 0.050. The observations and inferences are supported by particle‐in‐cell (PIC) numerical simulations. We find very good agreement in the reconnection rates. We also discuss the effects of asymmetries in the density, temperature and magnetic field strength on the Hall fields and length of the outflow jets. The event is associated with a substorm onset which began 7 min after the MMS observations. We analyze signatures of asymmetric reconnection earthward of the X‐line in a flapping and reconnecting magnetotail current sheetParticle‐in‐cell (PIC) simulations support Magnetospheric Multiscale mission (MMS) key observations and inferencesThe flapping episode was associated with a substorm onset We analyze signatures of asymmetric reconnection earthward of the X‐line in a flapping and reconnecting magnetotail current sheet Particle‐in‐cell (PIC) simulations support Magnetospheric Multiscale mission (MMS) key observations and inferences The flapping episode was associated with a substorm onset

In this paper, we derive a new drift‐kinetic method for estimating gradients in the plasma properties through a velocity space distribution at a single point. The gradients are intrinsically related to agyrotropic features of the distribution function. This method predicts the gradients in the magnetized distribution function and can predict gradients of arbitrary moments of the gyrotropic background distribution function. The method allows for estimates on density and pressure gradients on the scale of a Larmor radius, proving to resolve smaller scales than any method currently available to spacecraft. The model is verified with a set of fully kinetic VPIC particle‐in‐cell simulations. A drift‐kinetic method of measuring spatial gradients in the distribution function from local velocity‐space distributions is developedThis framework is extended to find gradients in arbitrary moments of the distribution functionThese methods are verified with simulation data, demonstrating resolution at the electron kinetic scale

We investigate an exhaust crossing of asymmetric guide field reconnection observed by Magnetospheric Multiscale (MMS) mission at Earth's dayside magnetopause. One MMS spacecraft (MMS 4) observes multicomponent electron distributions, including two counterstreaming electron beams, while the other three MMS spacecraft, with a separation of ∼30 km, record nearly isotropic electron distributions. As counterstreaming electrons are unstable for the electron two‐stream instability, our observations suggest that the electrostatic waves generated by the fast‐growing electron two‐stream instability can contribute to the rapid isotropization of electron distributions in the reconnection exhaust, indicating that wave‐particle interactions play an important role in electron dynamics. Rapid isotropization of electron distributions has been observed in the exhaust of asymmetric guide field reconnection by different MMS spacecraftThe high‐frequency electrostatic waves generated by the electron two‐stream instability can contribute to this processThis study indicates that wave‐particle interactions play an important role in electron dynamics in asymmetric guide field reconnection

Summary The principles of theH-balance for magnetic deep-sea measurements are mentioned, and the qualities of the balance are discussed.

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IN a communication on the daily magnetic variation to the Edinburgh meeting, 1936, of the Association of Terrestrial Magnetism and Electricity, A. G. McNish1states that the establishment of the magnetic observatory at Huancayo has led to the discovery of a daily variation of the horizontal force (H) “markedly different from those expected for such a region”, the amplitude being more than twice the value found from the analysis of S. Chapman. McNish has based his investigation on the assumption that the daily variation depends on magnetic co-ordinates, and points out that the daily variation of the declination varies considerably in a very narrow region at mag. lat. 0. The great daily variation of H at Huancayo is explained as an augmentation of the normal varying field originating from special circumstances. For Huancayo this augmentation, which is increasing when the distance of the magnetic equator from the geographic equator is increasing, is great.