Observational evidence of accelerating electron holes and their effects on passing ions

As a universal structure in space plasma, electron holes represent an obvious signature of nonlinear process. Although the theory has a 60-year history, whether electron hole can finally accelerate ambient electrons (or ions) is quite controversial. Previous theory for one-dimensional holes predicts that net velocity change of passing electrons (or ions) occurs only if the holes have non-zero acceleration. However, the prediction has not yet been demonstrated in observations. Here, we report four electron holes whose acceleration/deceleration is obtained by fitting the spatial separations and detection time delays between different Magnetospheric Multiscale spacecraft. We find that electron hole acceleration/deceleration is related to the ion velocity distribution gradient at the hole's velocity. We observe net velocity changes of ions passing through the accelerating/decelerating holes, in accordance with theoretical predictions. Therefore, we show that electron holes with non-zero acceleration can cause the velocity of passing ions to increase in the acceleration direction.

Particle-sounding of the spatial structure of kinetic Alfvén waves

Kinetic Alfvén waves (KAWs) are ubiquitous throughout the plasma universe. Although they are broadly believed to provide a potential approach for energy exchange between electromagnetic fields and plasma particles, neither the detail nor the efficiency of the interactions has been well-determined yet. The primary difficulty has been the paucity of knowledge of KAWs' spatial structure in observation. Here, we apply a particle-sounding technique to Magnetospheric Multiscale mission data to quantitatively determine the perpendicular wavelength of KAWs from ion gyrophase-distribution observations. Our results show that KAWs' perpendicular wavelength is statistically 2.4[Formula: see text] times proton thermal gyro-radius. This observation yields an upper bound of the energy the majority proton population can reach in coherent interactions with KAWs, that is, roughly 5.76 times proton perpendicular thermal energy. Therefore, the method and results shown here provide a basis for unraveling the effects of KAWs in dissipating energy and accelerating particles in a number of astrophysical systems, e.g., planetary magnetosphere, astrophysical shocks, stellar corona and wind, and the interstellar medium.

Direct observations of energy transfer from resonant electrons to whistler-mode waves in magnetosheath of Earth

Electromagnetic whistler-mode waves in space plasmas play critical roles in collisionless energy transfer between the electrons and the electromagnetic field. Although resonant interactions have been considered as the likely generation process of the waves, observational identification has been extremely difficult due to the short time scale of resonant electron dynamics. Here we show strong nongyrotropy, which rotate with the wave, of cyclotron resonant electrons as direct evidence for the locally ongoing secular energy transfer from the resonant electrons to the whistler-mode waves using ultra-high temporal resolution data obtained by NASA’s Magnetospheric Multiscale (MMS) mission in the magnetosheath. The nongyrotropic electrons carry a resonant current, which is the energy source of the wave as predicted by the nonlinear wave growth theory. This result proves the nonlinear wave growth theory, and furthermore demonstrates that the degree of nongyrotropy, which cannot be predicted even by that nonlinear theory, can be studied by observations.

Excitation of whistler-mode waves by cyclotron instability is considered as the likely generation process of the waves. Here, the authors show direct observational evidence for locally ongoing secular energy transfer from the resonant electrons to the whistler-mode waves in Earth’s magnetosheath.

Magnetic Reconnection Inside a Flux Rope Induced by Kelvin-Helmholtz Vortices

On 5 May 2017, MMS observed a crater-type flux rope on the dawnside tailward magnetopause with fluctuations. The boundary-normal analysis shows that the fluctuations can be attributed to nonlinear Kelvin-Helmholtz (KH) waves. Reconnection signatures such as flow reversals and Joule dissipation were identified at the leading and trailing edges of the flux rope. In particular, strong northward electron jets observed at the trailing edge indicated midlatitude reconnection associated with the 3-D structure of the KH vortex. The scale size of the flux rope, together with reconnection signatures, strongly supports the interpretation that the flux rope was generated locally by KH vortex-induced reconnection. The center of the flux rope also displayed signatures of guide-field reconnection (out-of-plane electron jets, parallel electron heating, and Joule dissipation). These signatures indicate that an interface between two interlinked flux tubes was undergoing interaction, causing a local magnetic depression, resulting in an M-shaped crater flux rope, as supported by reconstruction.

Electron Vorticity Indicative of the Electron Diffusion Region of Magnetic Reconnection

While vorticity defined as the curl of the velocity has been broadly used in fluid and plasma physics, this quantity has been underutilized in space physics due to low time resolution observations. We report Magnetospheric Multiscale (MMS) observations of enhanced electron vorticity in the vicinity of the electron diffusion region of magnetic reconnection. On 11 July 2017 MMS traversed the magnetotail current sheet, observing tailward-to-earthward outflow reversal, current-carrying electron jets in the direction along the electron meandering motion or out-of-plane direction, agyrotropic electron distribution functions, and dissipative signatures. At the edge of the electron jets, the electron vorticity increased with magnitudes greater than the electron gyrofrequency. The out-of-plane velocity shear along distance from the current sheet leads to the enhanced vorticity. This, in turn, contributes to the magnetic field perturbations observed by MMS. These observations indicate that electron vorticity can act as a proxy for delineating the electron diffusion region of magnetic reconnection.

Kinetic Range Spectral Features of Cross Helicity Using the Magnetospheric Multiscale Spacecraft

We study spectral features of ion velocity and magnetic field correlations in the magnetosheath and in the solar wind using data from the Magnetospheric Multiscale (MMS) spacecraft. High-resolution MMS observations enable the study of the transition of these correlations between their magnetofluid character at larger scales into the subproton kinetic range, previously unstudied in spacecraft data. Cross-helicity, angular alignment, and energy partitioning is examined over a suitable range of scales, employing measurements based on the Taylor frozen-in approximation as well as direct two-spacecraft correlation measurements. The results demonstrate signatures of alignment at large scales. As kinetic scales are approached, the alignment between v and b is destroyed by demagnetization of protons.

Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space

Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth's magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth's magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.

Direct measurements of two-way wave-particle energy transfer in a collisionless space plasma

Particle acceleration by plasma waves and spontaneous wave generation are fundamental energy and momentum exchange processes in collisionless plasmas. Such wave-particle interactions occur ubiquitously in space. We present ultrafast measurements in Earth's magnetosphere by the Magnetospheric Multiscale spacecraft that enabled quantitative evaluation of energy transfer in interactions associated with electromagnetic ion cyclotron waves. The observed ion distributions are not symmetric around the magnetic field direction but are in phase with the plasma wave fields. The wave-ion phase relations demonstrate that a cyclotron resonance transferred energy from hot protons to waves, which in turn nonresonantly accelerated cold He⁺ to energies up to ~2 kilo-electron volts. These observations provide direct quantitative evidence for collisionless energy transfer in plasmas between distinct particle populations via wave-particle interactions.

Electron Crescent Distributions as a Manifestation of Diamagnetic Drift in an Electron-Scale Current Sheet: Magnetospheric Multiscale Observations Using New 7.5 ms Fast Plasma Investigation Moments

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 × B drift 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.

Coalescence of Macroscopic Flux Ropes at the Subsolar Magnetopause: Magnetospheric Multiscale Observations

We report unambiguous in situ observation of the coalescence of macroscopic flux ropes by the magnetospheric multiscale (MMS) mission. Two coalescing flux ropes with sizes of ∼1  R_{E} were identified at the subsolar magnetopause by the occurrence of an asymmetric quadrupolar signature in the normal component of the magnetic field measured by the MMS spacecraft. An electron diffusion region (EDR) with a width of four local electron inertial lengths was embedded within the merging current sheet. The EDR was characterized by an intense parallel electric field, significant energy dissipation, and suprathermal electrons. Although the electrons were organized by a large guide field, the small observed electron pressure nongyrotropy may be sufficient to support a significant fraction of the parallel electric field within the EDR. Since the flux ropes are observed in the exhaust region, we suggest that secondary EDRs are formed further downstream of the primary reconnection line between the magnetosheath and magnetospheric fields.

Structure, force balance, and topology of Earth's magnetopause

The magnetopause deflects the solar wind plasma and confines Earth's magnetic field. We combine measurements made by the four spacecraft of the Magnetospheric Multiscale mission to demonstrate how the plasma and magnetic forces at the boundary affect the interaction between the shocked solar wind and Earth's magnetosphere. We compare these forces with the plasma pressure and examine the electron distribution function. We find that the magnetopause has sublayers with thickness comparable to the ion scale. Small pockets of low magnetic field strength, small radius of curvature, and high electric current mark the electron diffusion region. The flow of electrons, parallel and antiparallel to the magnetic field, reveals a complex topology with the creation of magnetic ropes at the boundary.

Rippled Quasiperpendicular Shock Observed by the Magnetospheric Multiscale Spacecraft

Collisionless shock nonstationarity arising from microscale physics influences shock structure and particle acceleration mechanisms. Nonstationarity has been difficult to quantify due to the small spatial and temporal scales. We use the closely spaced (subgyroscale), high-time-resolution measurements from one rapid crossing of Earth's quasiperpendicular bow shock by the Magnetospheric Multiscale (MMS) spacecraft to compare competing nonstationarity processes. Using MMS's high-cadence kinetic plasma measurements, we show that the shock exhibits nonstationarity in the form of ripples.

Loss of promoter IV-driven BDNF expression impacts oscillatory activity during sleep, sensory information processing and fear regulation

Posttraumatic stress disorder is characterized by hyperarousal, sensory processing impairments, sleep disturbances and altered fear regulation; phenotypes associated with changes in brain oscillatory activity. Molecules associated with activity-dependent plasticity, including brain-derived neurotrophic factor (BDNF), may regulate neural oscillations by controlling synaptic activity. BDNF synthesis includes production of multiple Bdnf transcripts, which contain distinct 5' noncoding exons. We assessed arousal, sensory processing, fear regulation and sleep in animals where BDNF expression from activity-dependent promoter IV is disrupted (Bdnf-e4 mice). Bdnf-e4 mice display sensory hyper-reactivity and impaired electrophysiological correlates of sensory information processing as measured by event-related potentials (ERP). Utilizing electroencephalogram, we identified a decrease in slow-wave activity during non-rapid eye movement sleep, suggesting impaired sleep homeostasis. Fear extinction is controlled by hippocampal-prefrontal cortical BDNF signaling, and neurophysiological communication patterns between the hippocampus (HPC) and medial prefrontal cortex (mPFC) correlate with behavioral performance during extinction. Impaired fear extinction in Bdnf-e4 mice is accompanied by increased HPC activation and decreased HPC-mPFC theta phase synchrony during early extinction, as well as increased mPFC activation during extinction recall. These results suggest that activity-dependent BDNF signaling is critical for regulating oscillatory activity, which may contribute to altered behavior.

Magnetospheric Multiscale Observations of the Electron Diffusion Region of Large Guide Field Magnetic Reconnection

We report observations from the Magnetospheric Multiscale (MMS) satellites of a large guide field magnetic reconnection event. The observations suggest that two of the four MMS spacecraft sampled the electron diffusion region, whereas the other two spacecraft detected the exhaust jet from the event. The guide magnetic field amplitude is approximately 4 times that of the reconnecting field. The event is accompanied by a significant parallel electric field (E_{∥}) that is larger than predicted by simulations. The high-speed (∼300  km/s) crossing of the electron diffusion region limited the data set to one complete electron distribution inside of the electron diffusion region, which shows significant parallel heating. The data suggest that E_{∥} is balanced by a combination of electron inertia and a parallel gradient of the gyrotropic electron pressure.

Magnetospheric Multiscale Satellites Observations of Parallel Electric Fields Associated with Magnetic Reconnection

We report observations from the Magnetospheric Multiscale satellites of parallel electric fields (E_{∥}) associated with magnetic reconnection in the subsolar region of the Earth's magnetopause. E_{∥} events near the electron diffusion region have amplitudes on the order of 100  mV/m, which are significantly larger than those predicted for an antiparallel reconnection electric field. This Letter addresses specific types of E_{∥} events, which appear as large-amplitude, near unipolar spikes that are associated with tangled, reconnected magnetic fields. These E_{∥} events are primarily in or near a current layer near the separatrix and are interpreted to be double layers that may be responsible for secondary reconnection in tangled magnetic fields or flux ropes. These results are telling of the three-dimensional nature of magnetopause reconnection and indicate that magnetopause reconnection may be often patchy and/or drive turbulence along the separatrix that results in flux ropes and/or tangled magnetic fields.

Transient, small-scale field-aligned currents in the plasma sheet boundary layer during storm time substorms

We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward/earthward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

Electron-scale measurements of magnetic reconnection in space

Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

Cloning and characterization of a putative fructosyltransferase and two putative invertase genes from the temperate grass Lolium temulentum L

The invertases of Lolium temulentum have been characterized at the enzyme level. However, studies on the expression of the genes coding for these enzymes have been lacking. To elucidate the role of acid 'invertase-like' genes in sucrose metabolism and carbon partitioning in Gramineae further, three 'invertase-like' homologous clones were isolated from L. temulentum cDNA expression libraries based on leaf tissue, using maize soluble invertase probes. The effect of developmental stage and alterations in carbohydrate status on the expression and tissue distribution of these genes was investigated. The three highly homologous genes (Inv 1:2, Inv 1:4, and FT 2:2) show different patterns of expression and different tissue distribution. Inv 1:2 was predominantly expressed in root tissue. Expression increased during the dark in root and tiller base tissue. Minimal variations in gene expression were observed in leaf tissue following changes in carbohydrate status. Inv 1:4 was predominantly expressed in tiller bases, leaf sheath, and leaf base, with increased expression in tissue samples in the dark period. FT 2:2 was also predominantly expressed in tiller bases, leaf sheath, and leaf base. Higher expression was observed in leaf tissue following increases in carbohydrate content, in a manner that paralleled the regulation and spatial occurrence of fructan in the leaf tissue. Whilst invertases and fructosyltransferases are difficult to distinguish at the level of the whole sequence, analysis of 5' sequence and specific amino acids allows discrimination which correlates with patterns of expression within the tissue. Based on expression patterns and sequence characteristics, it is proposed that Inv 1:2 and Inv 1:4 code for soluble acid invertases, whilst FT 2:2 codes for a fructosyltransferase.

Views of Earth's magnetosphere with the image satellite

The IMAGE spacecraft uses photon and neutral atom imaging and radio sounding techniques to provide global images of Earth's inner magnetosphere and upper atmosphere. Auroral imaging at ultraviolet wavelengths shows that the proton aurora is displaced equatorward with respect to the electron aurora and that discrete auroral forms at higher latitudes are caused almost completely by electrons. Energetic neutral atom imaging of ions injected into the inner magnetosphere during magnetospheric disturbances shows a strong energy-dependent drift that leads to the formation of the ring current by ions in the several tens of kiloelectron volts energy range. Ultraviolet imaging of the plasmasphere has revealed two unexpected features-a premidnight trough region and a dayside shoulder region-and has confirmed the 30-year-old theory of the formation of a plasma tail extending from the duskside plasmasphere toward the magnetopause.

Visualizing the distribution of elements within barley leaves by energy dispersive X-ray image maps (EDX maps)

X-ray image maps of transverse sections of barley leaf blades were compared with individual X-ray emission spectra from vacuoles of barley leaf mesophyll, epidermis and parenchymatous bundle sheath cells. Both forms of X-ray analysis revealed distinct patterns in element distribution within the leaf blade. Calcium and Cl predominated within the epidermal cell vacuoles whilst P appeared mainly in the mesophyll cell layer. Apparent accumulation of S and Mg within the bundle sheath cell vacuoles is discussed in relation to xylem unloading and sulphur assimilation.

The Extraction and Assay of 1-Kestose:Sucrose Fructosyl Transferase from Leaves of Wheat

Isolating the enzymes responsible for fructan synthesis in plants has been hampered by unsuitable assays used during purification. It is believed that there are two enzymes necessary for fructan synthesis in higher plants, one initiating synthesis utilizing sucrose as donor and the other elaborating the polymer using fructan oligomers as donor. In this paper, a rapid quantitative assay is described to measure the latter fructosyl transfer. The activity was absent from leaves that were not synthesizing fructan. Activity in crude extracts showed a hyperbolic dependence upon sucrose concentration. Activity against 1-kestose showed a pronounced optimum, suggesting that self-transfer also occurred.

Polysaccharide production in liquid cell suspension cultures of Phleum pratense L

The production of carbohydrates by cell suspension cultures of Phleum pratense (timothy grass) is described. Extracellular polysaccharides similar in monosaccharide composition to native cell wall polymers were accumulated, together with polymers of fructose (fructans). The fructans had similar properties to the intracellular reserve polymers found in intact plants, and were found in both cells and media of young, slow-growing cultures.Production of extracellular polysaccharides differed in cultures grown on sucrose or equimolar glucose/fructose as carbon source. These differences were observed only when autoclaved media were used, and were not related to changes in either pH or osmolarity. Autoclaving medium containing radioactive glucose and fructose produced a novel, unidentified labelled compound which was absent in medium containing labelled sucrose.

TANSLEY REVIEW NO. 5 FRUCTANS AND THE METABOLISM OF SUCROSE IN VASCULAR PLANTS

The occurrence, structure and metabolism of fructose polymers in tissues of vascular plants are discussed in relation to the metabolism of sucrose. Distinctions are made between long-term and short-term storage of such polymers and the regulatory mechanisms which govern accumulation are examined. The roles of various fructosyltransferases in the synthesis of the different fructan structures from sucrose are outlined. The potential selective advantages of the possession of fructan metabolism in different species are assessed with reference to possible roles as cryoprotectants, in osmotic control and as storage carbohydrates whose metabolism can continue at low temperatures (0 to 5°C). It is concluded that the complexity and variety of fructan structures and of the associated enzyme systems has resulted in an incomplete understanding of their physiology and biochemistry, but their significance as an alternative storage polysaccharide in both leaves and storage organs should not be underestimated. Contents I. Introduction II. The structure of fructans in vascular plants: variations on a theme 2 III. The enzymes of fructan synthesis: common elements and sources of structural diversity 5 IV. The comparative biology of fructan metabolism: diversity in occurrence and function 11 V. Concluding remarks 19 Acknowledgements 19 References 19.

The use of a temperature-profiled position transducer for the study of low-temperature growth in Gramineae : Equipment design and output interpretation

A device is described for measuring linear extension of grass leaves during controlled cooling and heating of the growing region. The instrument was employed to investigate the sensitivity to temperature of the expanding third and fourth leaves of Lolium temulentum L. seedlings. Using a stepped temperature profile it was established that there was no lag in the response of growth rate to rapid changes in temperature below 16°C. If cooling was continued to the point where growth ceased (1°C) but no further, then rates of growth on rewarming were enhanced over the chilling range and reverted to the original rate at 20°C. Cooling to successively lower subzero temperatures before rewarming abolished the hysteretic enhancement, progressively raised the temperature at which growth resumed and decreased the rate of extension until, at-5.3°C, no recovery occurred. The temperature sensitivity of growth, measured as Q10, was essentially constant when cooling from 20°C to 5°C, with 5°C-grown leaf tissue exhibiting a higher mean Q10 than tissue developed at 20°C. The possible physiological significance of these data is discussed.

The distribution of acid invertase in developing leaves of Lolium temulentum L

The levels of invertase (E.C. 3.2.1.26) activity were measured throughout the development of the fourth leaf of Lolium temulentum. No neutral invertase activity was detected. Soluble acid invertase activity fell during leaf extension but rose again after ligule formation. This rise continued into senescence and was accompanied by the appearance of activity in the insoluble fraction. Evidence is presented that the insoluble activity was not an artefact of preparation, and that it represented an extracellular acid invertase. Fractionation of soluble invertase by gel filtration showed the appearance of a high molecular weight form at the time when insoluble activity was rising. The relationships between the different forms of the enzyme are discussed, together with their roles in leaf development.

Cold-induced sweetening of tissue cultures of Solanum tuberosum L

Callus cultures derived from tubers of Solanum tuberosum L. cv. "Record" were transferred from a complete medium to a maintenance medium that lacked sugar and were then incubated at 2° or 25°. Incubation at 2° for 5 days led to an accumulation of sucrose. This accumulation did not occur at the expense of stored reducing sugars and was not found at 25°. Such cultures could be used for the study of cold-induced sweetening in potatoes.