Field-particle energy exchange is important to the magnetic reconnection process, but uncertainties regarding the time evolution of this exchange remain. We investigate the temporal dynamics of field-particle energy exchange during magnetic reconnection, using Magnetospheric Multiscale mission observations of an electron-only reconnection event in the magnetosheath. The electron energy is in local minimum at the x-line due to a density depletion, while the magnetic energy is in local maximum due to a guide field enhancement. The electromagnetic energy transport comes almost entirely from guide field contributions and is confined within the reconnection plane, while the most significant contribution to electron energy transport is independent of the drift velocity with additional out-of-plane signatures. Multi-spacecraft analysis suggests that the guide field energy is decreasing while the electron density is increasing, both evolving such that the system is moving toward a more uniform distribution of magnetic and thermal energy. The exchange of electromagnetic and thermal energy in collisionless plasmas is an important area of study to understand many space physics processes. The authors use in-situ, high resolution measurements from the MMS mission to examine the spatiotemporal evolution of the electron thermal and electromagnetic energy landscape during an encounter with a magnetic reconnection site in the Earth’s magnetosphere.

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.

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

Temporal, spatial, and velocity-space variations of electron phase space density are measured observationally and compared for the first time using the four magnetospheric multiscale (MMS) spacecraft at Earth's magnetopause. Equipped with these unprecedented spatiotemporal measurements offered by the MMS tetrahedron, we compute each term of the electron Vlasov equation that governs the evolution of collisionless plasmas found throughout the universe. We demonstrate how to use single spacecraft measurements to improve the resolution of the electron pressure gradient that supports nonideal parallel electric fields, and we develop a model to intuit the types of kinetic velocity-space signatures that are observed in the Vlasov equation terms. Furthermore, we discuss how the gradient in velocity-space sheds light on plasma energy conversion mechanisms and wave-particle interactions that occur in fundamental physical processes such as magnetic reconnection and turbulence.

The data included here is for an article submission to the Physics of Plasmas: MMS special Issue. There are electric field, magnetic field, and particle data files from MMS. There is a file from Particle-in-Cell simulations (pfd.xdmf), and there is a python notebook where some of the data was analyzed.

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 the peak reconnection rate has not been thoroughly discussed. We use a 2D particle-in-cell (PIC) simulation to examine how the non-ideal reconnection electric field evolves during the growth process and how it relates to changes near the x-line. We identify three phases of growth: 1) slow quasi-linear growth, 2) rapid exponential growth, and 3) tapered growth followed by negative growth after the reconnection rate peaks. Through analysis of the structural changes of the EDR, we associate the early phases with the breaking of x-line symmetry through the erosion of the pre-onset bipolar Ez and the emergence of a diverging Ex pattern at the neutral line in phase 1 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, relieving the electron-scale bottleneck and allowing large Poynting flux across the separatrices. We find that the rapid inflow of electromagnetic energy accumulates until the downstream electromagnetic energy density in phase 3 approaches 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.

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 R E ). 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 B and E fields. 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 d e (EDR) and ∼0.4 d i (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 examine the 11 July 2017 electron diffusion region (EDR)observed by the MagnetosphericMultiscale (MMS) mission using Poynting's theorem. The terms in Poynting's theorem are determined using a linear gradient approximation to obtain barycentric averages within the MMS tetrahedron. We find that Poynting's theorem is approximately balanced in the EDR and the balance is improved if the calculation of ∇·S→ is restricted to the LN plane. The work rate per unit volume J→·E→ is mostly balanced by the divergence of the electromagnetic energy flux ∇·S→ , indicating that the electromagnetic energy density remains relatively constant within the EDR during the encounter. We also use particle‐in‐cell (PIC) simulations to examine Poynting's theorem near an x line evolving in time. The central EDR in the simulation is characterized by approximate time independent balance in Poynting's theorem during reconnection growth, while the outer EDR exhibits time‐dependent fluctuations indicative of more chaotic behavior.

In this paper we report on a sequence of large‐amplitude Alfvénic fluctuations terminating in a field and flow discontinuity and their effects on electromagnetic fields and plasmas in the near‐magnetopause magnetosheath. An arc‐polarized structure in the magnetic field was observed by the Time History of Events and Macroscale Interactions during Substorms‐C in the solar wind, indicative of nonlinear Alfvén waves. It ends with a combined tangential discontinuity/vortex sheet, which is strongly inclined to the ecliptic plane and at which there is a sharp rise in the density and a drop in temperature. Several effects resulting from this structure were observed by the Magnetospheric Multiscale spacecraft in the magnetosheath close to the subsolar point (11:30 magnetic local time) and somewhat south of the geomagnetic equator (−33° magnetic latitude): (i) kinetic Alfvén waves; (ii) a peaking of the electric and magnetic field strengths where E · J becomes strong and negative (−1 nW/m 3 ) just prior to an abrupt dropout of the fields; (iii) evolution in the pitch angle distribution of energetic (a few tens of kilo‐electron‐volts) ions (H + , He n + , and O n + ) and electrons inside a high‐density region, which we attribute to gyrosounding of the tangential discontinuity/vortex sheet structure passing by the spacecraft; (iv) field‐aligned acceleration of ions and electrons that could be associated with localized magnetosheath reconnection inside the high‐density region; and (v) variable and strong flow changes, which we argue to be unrelated to reconnection at partial magnetopause crossings and likely result from deflections of magnetosheath flow by a locally deformed, oscillating magnetopause.

In alcoholic solutions (tinctures), the tricyclic triterpenoid alcohol, ambrein, which is usually the main ingredient of the natural product ambergris, undergoes photo-oxidation to a number of odorous products. Such tinctures are valuable in perfumery. Similar reactions are thought to occur in the marine environment, when flotsam and jetsam ambergris are exposed to sunlight. However, previous simulations of this process used artificial photosensitisers and did not include dark controls. We therefore conducted experiments in which ambrein in seawater (~1666 mg L-1) containing a photosensitiser, forms of which are found naturally in ambergris (5, 10, 15, 20-tetraphenyl-21H, 23H-porphine copper (II); 1% of ambrein w/w), was exposed to simulated natural sunlight for experimental periods of up to 6 h (approximately equivalent to 48 h natural exposure, Florida midday, mid-summer sunlight). Dark controls were treated in the same manner, without exposure to light. After 6 h exposure to light, total reaction products detectable by gas chromatography-mass spectrometry of solvent extracts, comprised about 1% by mass of the initial ambrein. However, unaccounted-for mass losses of ambrein were much greater than this (~50%), even in the dark, suggesting major losses of volatile products and/or non-recovery of some oxidation products by extraction. Photo-oxidation products included ambroxan, γ-dihydroionone, a tricyclic enol ether and possibly a related lactone. All of these have been reported previously in photoexposures of ambrein made under, arguably, less environmentally-realistic conditions. The latter products were not observed in dark controls however, suggesting they were only products of photo-oxidation.