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We report multi-spacecraft observations of ULF waves from Van Allen Probes (RBSP), Magnetospheric Multiscale (MMS), Time History of Events and Macroscale Interactions during Substorm (THEMIS), and Geostationary Operational Environmental Satellites (GOES). On August 31, 2015, global-scale poloidal waves were observed in data from RBSP-B, GOES and THEMIS from L=4 to L=8 over a wide range of magnetic local time (MLT). The polarization states varied towards purely poloidal polarity. In two consecutive orbits over 18 hours, RBSP-A and RBSP-B recorded gradual variation of the polarization states of the poloidal waves; the ratio (|Ba|/|Br|) decreased from 0.82 to 0.13. After the variation of polarization states, the poloidal ULF waves became very purely poloidal waves, localized in both L and MLT. We identify the poloidal wave as second harmonic mode with a large azimuthal wave number (m) of –232. From RBSP particle measurements we find evidence that the high-m poloidal waves during the polarization variations were powered by inward radial gradients and bump-on-tail ion distributions through the N=1 drift-bounce resonance. Most of the time, the dominant free energy source was inward radial gradients, compared with the positive gradient in the energy distribution of the bump-on-tail ion distributions.

Oxygen ions, O+, efficiently energized by weak fast shock in the mid-altitude cusp observed by Cluster on 7 November 2004 are investigated in this paper. An interplanetary fast shock hitting Earth ...

International audience; 11 Conjunction observations of the electromagnetic field and plasma by Cluster and TC-1 at the 12 dayside magnetosphere are presented to investigate the sequential flux ropes transferred from the 13 low latitude boundary layer (LLBL) to the high altitude cusp on 10 March 2004.Three sequential 14 flux ropes originating from the dayside low latitude magnetopause are first detected by TC-1. 15 After ~ 6 min, three sequential flux ropes accumulated with energetic oxygen ions are also 16 detected by Cluster in the high altitude cusp. The recurrence period of these flux ropes is ~ 3 min. 17 The number density of energetic oxygen ions in the cusp flux rope is ~ 0.25 cm-3 detected from 18 CIS/CODF instrument on Cluster. It is found that oxygen ions with energy lager than 10 keV have 19 a narrow pitch angle (less than 90 degree) distribution in the southern high altitude cusp. While 20 oxygen ions with energy less than 10 keV are distributed in a wide pitch angle from 0 to 180 21 degree. Counter-streaming energetic oxygen ions are found in these flux ropes in the high altitude 22 cusp .This result suggests that the oxygen ions with energy less than 10 keV in the high altitude 23 cusp have two source regions. One is from the dayside magnetopause and the other is from the 24 low altitude cusp. Our investigations provide evidence that flux ropes at dayside low latitude 25 magnetopause can carry energetic oxygen ions into the high altitude cusp region. 26 27 Three key points 28 1) Counter-streaming oxygen ions are observed in the flux ropes in the cusp. 29 2) Energetic oxygen ions accumulated within sequential flux ropes in the high-altitude cusp. 30 3) Conjunction observations present sequential FTEs transfer from the dayside LLBL to the cusp. 31 32

Energetic oxygen ions O+ (> 1 keV) observed by the Magnetospheric Multiscale (MMS) satellites at the dusk flank magnetopause during the phase 1a and 1b are investigated. There are 31 dusk flank magnetopause crossing events during intense substorms (AE > 500 nT) are identified. These 31 events of energetic O+ at the dusk flank magnetopause include 9 events during the expansion phase and 22 events during the recovery phase of intense substorms. It is noted that 9 events of energetic O+ ion at the dusk flank magnetopause during intense substorms expansion phase are all under the southward IMF conditions. The number density of energetic O+ at the dusk flank magnetopause ranges from 0.01 cm−3 to 0.2 cm−3. The maximum number density ratio of O+/H+ is ~ 0.055 during intense substorm recovery phase with AE index about 610 nT and under the northward interplanetary magnetic field (IMF). The number density ratio of O+/H+ also shows an exponential increase with the IMF By. While IMF Bz seems play a minor role in O+ abundance at the dusk flank magnetopause during intense substrom. Our observations suggest that energetic oxygen ions play a key role in the mass and energy transferring from the tail to the dayside in the magnetosphere during intense substorms.

Unipolar pulses of kinetic Alfven waves (KAW) are first observed in the near-Earth plasma sheet (NEPS) associated with dipolarizations during substorm expansion phases. Two similar events are studied with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations during substorms on 3 February 2008 and 7 February 2008. The unipolar pulses were located at a trough-like Alfven speed profile in the northern plasma sheet at a distance of 10–11 R E from Earth. The dominant wave components consist of a southward δ E z toward the neutral plane and a +δ B y toward the dusk. The |δ E z |/|δ B y | ratio was in the range of a few times the local Alfven speed, a strong indication of KAW nature. The wave Poynting flux was earthward and nearly parallel to the background magnetic field. The pulse was associated with an earthward field-aligned current carried by electrons. These observational facts strongly indicate a KAW eigenmode that is confined by the plasma sheet but propagates earthward along the field line. The KAW eigenmode was accompanied by short timescale (1 min) dipolarizations likely generated by transient magnetotail reconnection. The observed polarity of the KAW field/current is consistent with that of the Hall field/current in magnetic reconnection, supporting the scenario that the Hall fields/current propagate out from reconnection site as KAW eigenmodes. Aurora images on the footprint of THEMIS spacecraft suggest that KAW eigenmode may power aurora brightening during substorm expansion phase.

Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeVelectron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼ 5.5, Van Allen Probes (Radiation Belt Storm Probes)‐A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL‐GEO, THEMIS‐D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons., Key Points Unambiguous evidence of deep injections of MeV electrons from multispacecraftExtremely large electric fields (50 mV/m) associated with the dipolarizationStrong dipolarizations may supply significant MeV electrons to radiation belts

International audience; Singly charged oxygen ions, O+, energized by kinetic Alfvén wave eigenmode (KAWE) in the plasma sheet boundary layer during dipolarizations of two intense substorms, 10:07 UT on 31 August 2004 and 18:24 UT on 14 September 2004, are investigated by Cluster spacecraft in the magnetotail. It is found that after the beginning of the expansion phase of substorms, O+ ions are clearly energized in the direction perpendicular to the magnetic field with energy larger than 1 keV in the near-Earth plasma sheet during magnetic dipolarizations. The pitch angle distribution of these energetic O+ ions is significantly different from that of O+ ions with energy less than 1 keV before substorm onset that is in the quasi-parallel direction along the magnetic field. The KAWE with the large perpendicular unipolar electric field, Ez -20 mV/m, significantly accelerates O+ ions in the direction perpendicular to the background magnetic field. We present good evidences that O+ ion origin from the ionosphere along the magnetic field line in the northward lobe can be accelerated in the perpendicular direction during substorm dipolarizations. The change of the move direction of O+ ions is useful for O+ transferring from the lobe into the central plasma sheet in the magnetotail. Thus, KAWE can play an important role in O+ ion transfer process from the lobe into the plasma sheet during intense substorms.

An ion flux dropout near the dipolarization front (DF) at around X GSM = −11 RE in the Earth’s plasma sheet was observed by Time History of Events and Macroscale Interaction during substorms (THEMIS) on March 31, 2009. The ion differential energy fluxes at energies from 450 eV to 150 keV measured by the ESA and SST instruments from THC began to decrease about 2 s before the detection of the DF and reached a local minimum 6 s later. Then, the ion fluxes gradually increased to form a dropout around the DF. The spatial extent of the dropout was about 4,000 km. For energies above 20 keV, the ion fluxes after the dropout are greater than those before it, contrary to the fluxes at energies below 20 keV. The associated ion density variation indicates that the ion flux dropout coincides with the ion density dropout. Taking advantage of multipoint observations, THD, THC, and THE detected the same DF consecutively. Only THC detected an obvious ion flux dropout; THD observed an indistinct one about 2 s before THC; no high-energy (E > 30 keV) ion flux dropout was observed by THE. Our study suggests that the ion flux dropout may evolve with the earthward-propagating DF, and its properties can depend on locations relative to the DF.

The fine magnetic field structure of two successive plasmoids previously reported is investigated by magnetic rotation analysis using four Cluster satellite data. Between these two plasmoids, opposite trends of curvature radius (R-c) variations of the magnetic field lines from the boundary to the inner part are found. The different variations of R-c reflect that the two plasmoids have different magnetic configurations. The electric current density distributions for both plasmoids are found distinct. The B-y increase and abundant field-aligned currents in the narrow core region of the first plasmoid indicate that a possible magnetic flux rope (MFR) core exists inside. The results indicate that the first observed plasmoid is of a magnetic loop (ML) type (with possible MFR core) and the second plasmoid is of a magnetic flux rope (MFR) type. The coexistence of ML and MFR in the near-Earth plasma sheet may imply that multiple X line reconnection can occur by either an antiparallel or a component-parallel way.

The magnetic field dipolarization in the vicinity of substorm onset and during substorm expansion phase during the period of 06:00–06:40 UT on 15 February 2008 is investigated with observations from multiple probes of THEMIS. It is found that the magnetic dipolarization at the substorm onset (the onset time was about 06:14 UT) was not accompanied by obvious magnetic disturbance and ion bulk speed variation. The magnetic dipolarizations taking place during the substorm expansion phase observed by P4~(−10.97, 2.04, −3.03) RE and P3~(−11.32, 1.15, −3.10) RE were mostly accompanied by high speed earthward ion bulk flow, but the magnetic dipolarizations occurring during the substorm expansion phase observed by P5~(−9.45, 1.07, −2.85) RE were not accompanied by high speed earthward ion bulk flow. Before substorm onset THEMIS P3, P4, P5 all observed the Bx component fluctuation with a period of about 300 s. After substorm onset earthward high speed ion bulk flow and significant magnetic disturbances both occurred at P3 and P4 locations. These results indicate that there is no one-to-one relationship between the near-Earth magnetic dipolarization and the earthward ion bulk flow. In particular, the magnetic dipolarization occurring on the earthward side of the inner near-Earth plasma sheet is not accompanied by high speed earthward ion bulk flow. The dipolarization at substorm onset is a local and small scale phenomenon. There are multiple magnetic dipolarizations occurring during the substorm expansion phase. The dipolarization process is very complex and is not simply an MHD process. It is accompanied by some kinds of plasma instabilities, the plasma sheet azimuthal expansion not only by earthward ion bulk flow during substorm. A sharp increase of the AE index does not always give an accurate substorm onset time for substorm analysis.

Substorm injections bring energetic particles to the inner magnetosphere. But the role of the injected population in building up the storm time ring current is not well understood. By surveying Los Alamos National Laboratory geosynchronous data during 34 storm main phases, we show evidence that at least some substorm injections can contribute to substorm-time scale SYM-H/Dst depressions in the main phase of storms. For event studies, we analyze two typical events in which the main-phase SYM-H index exhibited stepwise depressions that are correlated with particle flux enhancement due to injections and with AL index. A statistical study is performed based on 95 storm time injection events. The flux increases of the injected population (50–400 keV) are found proportional to the sharp SYM-H depressions during the injection interval. By identifying dispersionless and dispersive injection signals, we estimate the azimuthal extent of the substorm injection. Statistical results show that the injection regions of these storm time substorms are characterized with an azimuthal extent larger than 06:00 magnetic local time. These results suggest that at least some substorm injections may mimic the large-scale enhanced convection and contribute to sharp decreases of Dst in the storm main phase.

On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front (i.e., southward turning). When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times (MLTs) all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.

Based on measurements of FGM and HIA on board TC-1 at its apogee on September 14, 2004, we analyzed the ion high-speed flows in the near-Earth plasma sheet observed during the substorm expansion phase. Strong tailward high-speed flows (Vx ∼ −350 km/s) were first seen at about X ∼ −13.2 RE in near-Earth magnetotail, one minute later the flows reversed from tailward to earthward. The reversal process occurred quickly after the substorm expansion onset. The near-Earth magnetotail plasma sheet was one of key regions for substorm onset. Our analysis showed that the ion flow reversal from tailward to earthward was likely to be in close relation with the substorm expansion initiation and might play an important role in triggering the substorm expansion onset.

We analyze Double Star TC-1 magnetic field data from July to September in 2004 and find that plasmoids exist in the very near-Earth magnetotail. It is the first time that TC-1 observes the plasmoids in the magnetotail at X>-13 R-E. According to the difference of the magnetic field structure in plasmoids, we choose two typical cases for our study: the magnetic flux rope on August 6 with the open magnetic field and the magnetic loop on September 14 with the closed magnetic field. Both of the cases are associated with the high speed earthward flow and the magnetic loop is related to a strong substorm. The ions can escape (from the magnetic flux rope along its open field line, but the case of the closed magnetic loop can trap the ions. The earthward flowing plasmoids observed by TC-1 indicate that the multiple X-line magnetic reconnection occurs beyond the distance of X=-10 R-E from the earth.

Kinetic Alfven waves (KAWs) driven by the diamagnetic drift instability that is excited by the density inhomogeneity in low- β plasmas, such as plasmas in the auroral region, are investigated by adopting the particle aspect analysis and loss-cone distribution function. The results obtained in this paper indicate that the propagation and evolution of kinetic Alfven waves decrease and the kinetic Alfven wave excitation becomes not easier with increasing loss-cone index J . But the spatial scales of the perpendicular perturbation driving kinetic Alfven waves have a decreasing tendency with the larger values of J , which perhaps is in relation with the decreasing width of loss-cone. A single hump appears in the plots of the growth rate of the instability when J = 2 . But the hump cannot emerge when J = 0 or J = 1 . The density inhomogeneity of ions plays an important role in driving KAWs and it cannot be ignored. KAWs can be easier driven and KAWs can propagate and evolve faster with the increasing level of density inhomogeneity. However, the range of the perpendicular wave number of the wave instability decreases, namely, the longer the scale of perpendicular disturbance the easier the excitation of KAW. As the density inhomogeneity increases, the tendency of numerical solutions of the dispersion relation is similar to that obtained by the kinetic theory and Maxwellian distribution function ( Duan and Li, 2004 ). But the profiles of the plots of numerical solutions are different. This means that the velocity distribution function of particles is important for KAW driven in magnetoplasmas, especially in the active regions of the magnetosphere, such as auroral region, and plasma sheet boundary.

Taken the two-fluid magnetohydrodynamic (MHD) model to describe ion and electron motion, the properties of solitary kinetic Alfven waves (SKAWs) in the low-β plasma of the inertial limit region (ILR) were studied based on the undisturbed theory. The solitons were taken as the classical particles and the Sagdeev potential function was derived according to the foundational equations, then the SKAWs solutions were obtained by numerical calculation. The results show that the influence of hot ions on the properties of solitary kinetic Alfven waves can't be neglected and both dip solitons and hump solitons exist in the ILR. These results agree well with the data detected by the Freja satellite over the auroral region. As Alfven solitary waves accompanied by the parallel electric field, take an important part to accelerate the charged particles. This provides a novel kind of physical mechanism for the acceleration of polar aurora in the auroral region.

Bloomfield’s book Language has long been recognized for laying down the foundation of formal descriptive linguistic analysis. However, he was criticized too often for his dismissal of serious study of meaning in linguistics. The fact is that in his 1933 book Language, a separate chapter is devoted to the discussion of meaning and some of the most important formal units of linguistic analysis introduced by Bloomfield like phoneme and morpheme could not have been properly defined without involving meaning. He forcefully challenged the contemporary popular mentalism in linguistic study, as has often been bypassed. His contention that linguistic study must start from form not meaning should not be taken at face value as neglect of meaning but in the historical context as an opposition to mentalistic subjective interpretation of meaning.

A substorm dispersionless injection event observed during the storm recovery phase on 11 March 1998 at geosynchronous orbit is carefully studied. The event shows the notable characteristics that for energetic ions the flux enhancement ratio before and after injection increases and remains elevated with increasing energy, while for energetic electrons it tends to decrease with increasing energy. In order to explain the unique injection feature, the authors propose a possible mechanism that velocity space diffusion in common to electric acceleration adjusts the particle injection state. Spectral characteristics of four different phases (pregrowth phase, the growth phase, the substorm expansion phase, and the recovery phase) have been investigated. The differential fluxes of electrons from 50 keV to 1.5 Mev and ions from 50 keV to 1.2 MeV measured by Synchronous Orbit Plasma Analyzer (SOPA) instrument onboard LANL satellite 1991-080 are found to be best fitted with the three-parameter kappa distribution function (f similar to A(0) . E[1 + E / (kappa E-0)](-kappa-1)) by Levenberg-Marquardt and Universal Global Optimization methods. The evolutions of the three parameters in the above kappa distribution in different substorm phases have been depicted for both electrons and ions. In each phase, E-0 and kappa show an approximately linear relationship kappa(E-0) = kappa(0) + eta E-0. This linear relationship can be obtained by solving the velocity space diffusion equation with an initial superthermal kappa distribution. Ion and electron are found to have opposite trend of parameters kappa(0) and eta in each phase, which indicates that the different species of particles exert different velocity space diffusion processes so that their flux enhancement ratios before and after injection are rather different. This implies that not only electric field acceleration, but also velocity space diffusion plays a very important role in the particle injection.

Low frequency electromagnetic fluctuations in the vicinity of a magnetospheric substorm onset were investigated using simultaneous observations by THEMIS multiple probes in the near-Earth plasma sheet in the magnetotail. The observations indicate that in the vicinity of a substorm onset, kinetic Alfven waves can be excited in the high-β plasma sheet (β=2µ0nT/B2, the ratio of plasma thermal pressure to magnetic pressure) within the near-Earth magnetotail. The kinetic Alfven wave has a small spatial scale in the high-β plasma. The parallel electric field accompanying kinetic Alfven waves accelerates the charged particles along the magnetic field. The kinetic Alfven waves play an important role in the substorm trigger process, and possibly in the formation of a substorm current wedge.