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Metallic and silicate ions carry essential information about the evolution of the Earth and near-Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this presentation, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors (RAPID) on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin, as indicated by correlations with heavy ion observations from the ACE spacecraft at L1. Sputtering off the Moon is another possible source of the observed heavy ions.

The dynamics of fluxes of thermal and suprathermal H+ and O+ ions and the pressure variations of these components during 11 events of magnetic field dipolarization in the plasma sheet of the geomagnetic tail are analyzed based on Cluster satellite observations. It was found that the energy of H+ and O+ ions corresponding to the maximum flux approached or exceeded the upper energy threshold of CODIF thermal plasma mass spectrometers (~40 keV) in all of the events. During such periods, the determined values of the density, temperature, and pressure in an energy range up to 40 keV are underestimated as compared to the actual values. To determine the pressure during such intervals, we used measurements of the ion-component fluxes in an energy range up to 1.3 MeV based on a joint analysis of observations of CODIF and RAPID energy-mass spectrometers. As a result, it was found that the ion pressure during dipolarization with the high-energy component of the spectrum taken into account can be several times higher than the pressure determined in the range up to 40 keV. Using the superposed epoch analysis, we showed that the error associated with underestimation of the pressure of the H+ and O+ ion components is largest during the dipolarization growth phase. The underestimation is most significant for the O+ ion pressure.

We study acceleration of energetic electrons in an earthward plasma jet due to magnetic reconnection in the Earth magnetotail for one case observed by Cluster. The case has been selected based on the presence of high fluxes of energetic electrons, Cluster being in the burst mode and Cluster separation being around 1,000 km that is optimal for studies of ion scale physics. We show that two characteristic acceleration mechanisms are operating during this event. First, significant acceleration is achieved inside the magnetic flux pile-up of the jet, the acceleration mechanism being consistent with betatron acceleration. Second, strong energetic electron acceleration occurs in magnetic flux rope like structure forming in front of the magnetic flux pile-up region. Energetic electrons inside the magnetic flux rope are accelerated predominantly in the field-aligned direction and the acceleration can be due to Fermi acceleration in a contracting flux rope.

The Cluster mission has produced a large data set of electron flux measurements in the Earth's magnetosphere since its launch in late 2000. Electron fluxes are measured using Research with Adaptive Particle Imaging Detector (RAPID)/Imaging Electron Spectrometer (IES) detector as a function of energy, pitch angle, spacecraft position, and time. However, no adiabatic invariants have been calculated for Cluster so far. In this paper we present a step-by-step guide to calculations of adiabatic invariants and conversion of the electron flux to phase space density (PSD) in these coordinates. The electron flux is measured in two RAPID/IES energy channels providing pitch angle distribution at energies 39.2-50.5 and 68.1-94.5 keV in nominal mode since 2004. A fitting method allows to expand the conversion of the differential fluxes to the range from 40 to 150 keV. Best data coverage for phase space density in adiabatic invariant coordinates can be obtained for values of second adiabatic invariant, K, similar to 10(2), and values of the first adiabatic invariant mu in the range approximate to 5-20 MeV/G. Furthermore, we describe the production of a new data product "LSTAR," equivalent to the third adiabatic invariant, available through the Cluster Science Archive for years 2001-2018 with 1-min resolution. The produced data set adds to the availability of observations in Earth's radiation belts region and can be used for long-term statistical purposes., Zweitver��ffentlichungen der Universit��t Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1192

Metallic and silicate ions carry essential information about the evolution of the Earth and near‐Earth small bodies. Despite this, there has so far been very little focus on ions with atomic masses higher than oxygen in the terrestrial magnetosphere. In this paper, we report on abundances and properties of energetic ions with masses corresponding to that of silicon (Si) and iron (Fe) in Earth's geospace. The results are based on a newly derived data product from the Research with Adaptive Particle Imaging Detectors on Cluster. We find traces of both Si and Fe in all of the regions covered by the spacecraft, with the highest occurrence rates and highest intensities in the inner magnetosphere. We also find that the Fe and Si abundances are modulated by solar activity. During solar maximum, the probability of observing Fe and Si in geospace increases significantly. On the other hand, we find little or no direct correlation between geomagnetic activity and Si and Fe abundance in the magnetosphere. Both Si and Fe in the Earth's magnetosphere are inferred to be primarily of solar wind origin., Key Points: A new data product from the Cluster mission is utilized to study heavy ions in geospace. Traceable amounts of silicon (Si) and iron (Fe) are found in all regions of space traversed by Cluster. The detected Si and Fe are most likely of solar wind origin., Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) http://dx.doi.org/10.13039/501100002946

The dynamics of high-energy electron fluxes (with energies over 40 keV) is analyzed in 13 events of magnetic field dipolization observed by the Cluster satellites in the near-tail of the Earth magnetosphere. In all of the events, the observed energetic electron fluxes are enhanced simultaneously with initial dipolization. Good correlation (correlation coefficient >0.6) is observed between the dynamics of the energetic electron fluxes with energies up to 90 keV and the BZ component of the magnetic field. Electron fluxes with higher energies display a decline of correlation with the magnetic field. The increase in electron fluxes with energies up to 90 keV during dipolization development is shown to be mainly due to the mechanism of betatron acceleration. The dynamics of electron fluxes with higher energies is poorly described by the betatron scenario and requires consideration of other, probably nonadiabatic, mechanisms.

Usually, for the plasma pressure estimation in the plasma sheet ion observations in the energy range up to ~40 keV are used. However, the thermal part of the distribution function can pass beyond the high energy threshold of an instrument during active events like dipolarizations. In such cases the entire ion population is not measured and the ion pressure can be underestimated. We study this problem by using Cluster mission observations provided by two instruments: thermal plasma instrument - CODIF (up to 38 keV) and suprathermal instrument - RAPID (from 40 up to 1500 keV). We analyzed 11 dipolarization events and showed that in all events the maximum of ion energy flux was shifted to high energy threshold of CODIF instrument. Simultaneously, the energy flux increase in suprathermal energy range was observed by RAPID. For H+ and O+ ion components we calculate the pressure of suprathermal population and showed that the total pressure estimated by using both CODIF and RAPID instruments at some intervals exceeds the pressure estimated only from CODIF data up to 5 times. The superposed epoch analysis applied to 11 dipolarization events from our data base showed that the total pressure of H+ and O+ ion components can be in 2-5 times underestimated in the course of dipolarization.

International audience; Baryonic matter in geospace is almost exclusively in a plasma state, with protons (H +) and to some extent ionized helium (He) and oxygen (O) being the dominant ion species. But also other heavier ion species and even molecular ions are present in geospace. The Research with Adaptive Particle Imaging Detectors (RAPID) on board the Cluster satellites can identify and characterize some of these ions by utilizing their measured time of flight and energy. Usually, the measurements are then assigned into three discrete species channels; protons (H +), helium (He), and a common channel for carbon, nitrogen, and oxygen (CNO), each with flux, energy, and angular information. But RAPID also has a Direct Event (DE) diagnostic mode in which the full time of flight and energy information for a limited number of incident particles are stored. With knowledge about energy losses in the various detector parts, it is then possible to derive the atomic mass of the incident particle. In this paper we report on results from a study of Cluster DE events during the years 2001-2018, with a particular emphasis of iron (Fe) ions. We show that suprathermal Fe ions can be found all over geospace covered by Cluster, and that the time variation is consistent with modulation by geomagnetic disturbances and solar activity. We do not find any clear correlations between detection of suprathermal Fe and meteor showers or sputtering off the moon.

Particle injections in the magnetosphere transport electrons and ions from the magnetotail to the radiation belts. Here we consider generation mechanisms of dispersionless injections, namely, those with simultaneous increase of the particle flux over a wide energy range. In this study we take advantage of multisatellite observations which simultaneously monitor Earth's magnetospheric dynamics from the tail toward the radiation belts during a substorm event. Dispersionless injections are associated with instabilities in the plasma sheet during the growth phase of the substorm, with a dipolarization front at the onset and with magnetic flux pileup during the expansion phase. They show different spatial spread and propagation characteristics. Injection associated with the dipolarization front is the most penetrating. At geosynchronous orbit (6.6R(E)), the electron distributions do not have a classic power law fit but instead a bump on tail centered on similar to 120keV during dispersionless electron injections. However, electron distributions of injections associated with magnetic flux pileup in the magnetotail (13R(E)) do not show such a signature. We surmise that an additional resonant acceleration occurs in between these locations. We relate the acceleration mechanism to the electron drift resonance with ultralow frequency waves localized in the inner magnetosphere.

The Cluster mission, launched in 2000, has produced a large database of electron flux intensity measurements in the Earths magnetosphere by the Research with Adaptive Particle Imaging Detector (RAPID)/ Imaging Electron Spectrometer (IES) instrument. However, due to background contamination of the data with high-energy electrons (>400 keV) and inner- zone protons (230-630 keV) in the radiation belts and ring current, the data have been rarely used for inner-magnetospheric science. The current paper presents two algorithms for background correction. The first algorithm is based on the empirical contamination percentages by both protons and electrons. The second algorithm uses simultaneous proton observations. The efficiencies of these algorithms are demonstrated by comparison of the corrected Cluster/RAPID/IES data with Van Allen Probes/Magnetic Electron Ion Spectrometer (MagEIS) measurements for 2012-2015. Both techniques improved the IES electron data in the radiation belts and ring current.Yearly averaged flux intensities of the two missions show the ratio of measurements close to 1. IES corrected measurements were also compared with Arase Medium-Energy Particle Experiments-Electron Analyzer (MEP-e) electron data during two conjunction periods in 2017 and also exhibited ratio close to 1. We demonstrate a scientific application of the corrected IES electron data analyzing its evolution during solar cycle. Spin-averaged yearly mean IES electron intensities in the outer belt for energies 40-400 keV at L-shell between 4 and 6 showed high positive correlation with AE index and solar wind dynamic pressure during 2001- 2016. Relationship between solar wind dynamic pressure and IES electron measurements in the outer radiation belt was derived as a uniform linear-logarithmic equation.

International audience; The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (Pdyn) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models.

Erreur sur l'affiliation : Dominique Delcourt : 1, 21 : Laboratoire de Physique des Plasmas, Ecole Polytechnique, CNRS, france2, LPC2E, UMR7328, CNRS, Université d'Orléans, 45071 Orléans Cedex 2; International audience; Magnetic field dipolarizations are often observed in the magnetotail during substorms. These generally include three temporal scales: (1) actual dipolarization when the normal magnetic field changes during several minutes from minimum to maximum level; (2) sharp Bz bursts (pulses) interpreted as the passage of multiple dipolarization fronts with characteristic time scales < 1 min, and (3) bursts of electric and magnetic fluctuations with frequencies up to electron gyrofrequency occurring at the smallest time scales (≤ 1 s). We present a numerical model where the contributions of the above processes (1)-(3) in particle acceleration are analyzed. It is shown that these processes have a resonant character at different temporal scales. While O+ ions are more likely accelerated due to the mechanism (1), H+ ions (and to some extent electrons) are effectively accelerated due to the second mechanism. High-frequency electric and magnetic fluctuations accompanying magnetic dipolarization as in (3) are also found to efficiently accelerate electrons.

This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some extent electrons) can be more effectively accelerated due to the mechanism (C) than the single dipolarization (B). It is found that high-frequency electric and magnetic fluctuations accompanying multiple DFs (D) can strongly accelerate electrons e− and really weakly influence other populations of plasma. The results of modeling demonstrated clearly the distinguishable spatial and temporal resonance character of particle acceleration processes. The maximum particle energies depending on the scale of the magnetic acceleration region and the value of the magnetic field are estimated. The shapes of energy spectra are discussed.This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some exten...

Modelling plasma entry in the polar cusp has been successful in reproducing ion dispersions observed in the cusp at low and mid-altitudes. The use of a realistic convection pattern, when the IMF-By is large and stable, allowed Wing et al. (2001) to predict double cusp signatures that were subsequently observed by the DMSP spacecraft. In this paper we present a cusp crossing where two cusp populations are observed, separated by a gap around 1° Invariant Latitude (ILAT) wide. Cluster 1 (C1) and Cluster 2 (C2) observed these two cusp populations with a time delay of 3 min, and about 15 and 42 min later Cluster 4 (C4) and Cluster 3 (C3) observed, respectively, a single cusp population. A peculiarity of this event is the fact that the second cusp population seen on C1 and C2 was observed at the same time as the first cusp population on C4. This would tend to suggest that the two cusp populations had spatial features similar to the double cusp. Due to the nested crossing of C1 and C2 through the gap between the two cusp populations, C2 being first to leave the cusp and last to re-enter it, these observations are difficult to be explained by two distinct cusps with a gap in between. However, since we observe the cusp in a narrow area of local time post-noon, a second cusp may have been present in the pre-noon sector but could not be observed. On the other hand, these observations are in agreement with a motion of the cusp first dawnward and then back duskward due to the effect of the IMF-By component.

Hot flow anomalies (HFAs) were first discovered in the early 1980s at the bow shock of the Earth. In the 1990s these features were studied, observed and simulated very intensively and many new missions focused the attention to this phenomenon again. Many basic features and the HFA formation mechanism were clarified observationally and using hybrid simulation techniques. We described previous observational, theoretical and simulation results in the research field of HFAs. We introduced HFA observations performed at the Earth, Mars, Venus and Saturn in this paper. We share different observation results of space mission to give an overview to the reader. Cluster multi-spacecraft measurements gave us more observed HFA events and finer, more sophisticated methods to understand them better. In this study, HFAs were studied using observations of the Cluster magnetometer and the Cluster plasma detector aboard the four Cluster spacecraft. Energetic particle measurements (28.2-68.9 keV) were also used to detect and select HFAs. We studied several specific features of tangential discontinuities generating HFAs on the basis of Cluster measurements in the period February-April 2003, December 2005-April 2006 and January-April, 2007, when the separation of spacecraft was large and the Cluster fleet reached the bow shock. We have confirmed the condition for forming HFAs, that the solar wind speed is higher than the average. This condition was also confirmed by simultaneous ACE magnetic field and solar wind plasma observations at the L1 point 1.4 million km upstream of the Earth. The measured and calculated features of HFA events were compared with the results of different previous hybrid simulations. During the whole spring season of 2003, the solar wind speed was higher than the average. Here we checked whether the higher solar wind speed is a real condition of HFA formation also in 2006 and 2007., review paper, 11 pages, 11 figures, published in 2010

For energetic particle measurements whose spectra follow a power law, it is often challenging to define a characteristic ("effective") energy of an energy channel. In order to avoid time-consuming calculations, the geometric mean is often used as an approximation for the effective energy. This approximation is considered to be pretty good. It is, however, potentially inadequate in cases with wide energy channels and soft spectral slopes. In order to determine the limits of the goodness of the approximation, we derive formulas to calculate the deviation of the effective energy, phase space density and energy density based on the geometric mean approximation from those based on the power law. The results show that the geometric mean approximation is usually adequate and that corrections are needed only in extraordinary cases.

In a companion paper we have reported results from a survey of strong energetic ion (E > 25 keV) anisotropies in the central geomagnetic tail based on 2 years of data from the ISEE 2 spacecraft. Here we extend this study with particular emphasis on the relation of high ion anisotropies to recent models of geomagnetic substorms and include magnetic field and ground-based data. Beyond 16 RE downtail distance, we find a correlation between the magnetic field north-south component (Bz) and the streaming direction of the energetic ions. Earthward ion streaming is observed almost exclusively when Bz is positive while tailward streaming tends to occur with negative Bz. Strong ion anisotropies are magnetic field aligned rather than perpendicular to it suggesting that most of them are observed at the plasma sheet boundary. However, they are also found in the central plasma sheet. A superposed epoch analysis using the AL index yields a relation between substorm phases and the observation of high ion anisotropies. Earthward streaming at larger distances from the Earth and/or the neutral sheet usually occurs during substorm recovery while earthward streaming closer to the Earth and tailward streaming events are related to the substorm expansion phase. Three events characterized by strong tailward ion and plasma streaming detected first changing to earthward streaming later on are presented in some detail. The overall features of two of these events strongly suggest the formation of a magnetic neutral line earthward of the satellite at substorm onset moving tailward around recovery. While most observations during the third event also indicate such a sequence, there are some puzzling details which do not match this interpretation. Although a certain By signature proposed by numerical simulations of near-Earth reconnection could not be found, we conclude that the statistical properties of strong ion anisotropies can consistently be explained in terms of the near-Earth neutral line model of substorms if the substorm neutral line sometimes forms well inside the ISEE orbit. Other recently published models of substorm onset such as the thermal catastrophe model and the current disruption model can also account for part of the observations but still require further refinement.

During 1978 and 1979, the medium energy particles experiment on board the ISEE 2 spacecraft (apogee 22.7 RE) collected almost 122 days of data in the central region of the Earth's magnetotail. We have surveyed 16-s averages of the energetic ion (E > 25 keV) and plasma measurements in order to establish the statistical properties of high ion anisotropy events (|A| > 1) which are frequently observed in the near-Earth plasma sheet. Our major findings from the analysis of 1944 high-anisotropy samples (HAS) are as follows: (1) Strong energetic ion anisotropies are not maintained over long periods of time but occur in bursts lasting for fractions of a minute up to a few minutes. (2) For almost 80% of the HAS, the anisotropy vector points either earthward or tailward rather than across the tail (3) The ratio of HAS toward the Earth and HAS toward the tail is approximately 4.8:1. (4) The probability of observing high-anisotropy events is well enhanced beyond ≈16 RE downtail distance, on the duskside, and close (within 2–3 RE) to the neutral sheet. (5) Strong tailward anisotropies can be observed anywhere in the near-Earth plasma sheet. However, their occurrence frequency is considerably above average beyond xSE ≈ −19 RE and within 2 RE of the neutral sheet. (6) Both plasma bulk flow and ion anisotropy at higher energy (>115 keV) are generally in the same direction as the energetic ion anisotropy at E > 25 keV. (7) Streaming energetic electron populations in the same direction as the ions are significantly more often observed when the ions are streaming tailward than simultaneously with earthward streaming ions when the electrons are usually isotropic. We conclude that statistically the observation of strong tailward ion streaming indicates the existence of a particle source in the near-Earth magnetotail between the spacecraft and the Earth. Certain features suggest that this source might be identical with a near-Earth magnetic neutral line.

The RAPID instrument on board the four Cluster spacecraft delivers 3-D distributions of energetic (≳ 30 keV) ion and electron flux for up to eight energy channels. To make this data set available to the general scientific community, both during the operations phase and beyond the end of the mission, the RAPID Team is delivering processed data to the Cluster Active Archive (CAA). These data consist of both fluxes generated with the best current calibrations available, as well as raw count rates for knowledgeable users. Diagnostic products, caveats, documentation, and summary plots are also part of the deliverables. The intention is that once the Cluster Mission is completed and the instrument teams disbanded, this will be the sole repository of all available RAPID data and knowledge about it. This article gives an overview of the RAPID data products at CAA, and is intended to summarize the more complete description given in the Interface Control Document.

We present a method to combine spectral information from the Cluster RAPID (Research with Adaptive Particle Imaging) and CIS (Cluster Ion Spectroscopy) instruments. Preliminary results from the magnetotail show that the kappa distribution can fit the ion distributions in the magnetotail, for example in thin plasma sheets during quiet and disturbed times with kappa factors ≃ 4.4 and ≃ 10, respectively. With the most recent RAPID and CIS/CODIF calibration files the average ratio of CIS fluxes (approximated using the kappa-fit to the effective energy of the first RAPID energy channel) to the RAPID fluxes at the first energy channel is about 0.74 ± 0.24. This result is perfectly acceptable for these two experiments, based on two very different measurement principles, therefore no further spectral shift or recalibrations are needed.

[1] We use multipoint observation data by Cluster during time periods when the interspacecraft separation distance was between 1 and 1.5 Earth radii in order to study the physical processes related to diffuse ions at

[1] The Energetic Particles Detector and magnetometer measurements on Galileo showed that the Jovian magnetosphere undergoes reconfiguration processes which are very similar to the characteristics of a terrestrial substorm. At Jupiter the reconfiguration process occurs quasi-periodically with a repetition period of several days. In the terrestrial magnetosphere periodic substorms have been observed during magnetic storms. The comparison of the periodic magnetospheric disturbances at Jupiter and Earth shows that they are similar in dynamic features as well as in spatial distribution but have different energy sources. In the case of Earth, the well-established energy source is the solar wind. In the case of the Jovian magnetosphere, it is believed that internal energy is supplied by the fast planetary rotation and the moon Io which releases ∼1000 kg s−1 of plasma into the magnetosphere. It is established that the energy accumulation and subsequent release lead to similar features in the magnetospheres of both planets. The particle data show periodic intensity fluctuations and plasma pressure variations. In addition, recurring signatures of stretching and dipolarization are observed in the magnetic field at the terrestrial and Jovian magnetospheres. Furthermore, the release process is associated with an intensification of auroral emissions. The typical phases for terrestrial substorms like growth, expansion and recovery are also found in the periodic substorms at Jupiter. As a lesson taken from the Jovian magnetosphere it is proposed that under certain conditions periodic magnetospheric substorms at Earth can be driven by mass-loading from the plasmasphere.

[1] The composition of ions plays a crucial role for the fundamental plasma properties in the terrestrial magnetosphere. We investigate the oxygen-to-hydrogen ratio in the near-Earth magnetosphere from −10 RE 274 keV O+ ion intensities, relative to the corresponding hydrogen intensities; (3) In contrast to ∼10 keV ions, the >274 keV O+ions show the strongest acceleration during growth phase and not during the expansion phase itself. This suggests a connection between the energy input to the magnetosphere and the effective energization of energetic ions during growth phase; (4) The ratio between quiet and disturbed times for the intensities of ion ionospheric outflow is similar to those observed in the near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic ion intensity during disturbed time is likely due to the intensification and the effective acceleration of the ionospheric source. In conclusion, the energization process in the near-Earth magnetosphere is mass dependent and it is more effective for the heavier ions.

Open questions concerning structures and dynamics of diffusion regions and electron acceleration in collisionless magnetic reconnection are addressed based on data from the four-spacecraft mission Cluster and particle-in-cell simulations. Using time series of electron distribution functions measured by the four spacecraft, distinct electron regions around a reconnection layer are mapped out to set the framework for studying diffusion regions. A spatially extended electron current sheet (ecs), a series of magnetic islands, and bursts of energetic electrons within islands are identified during magnetotail reconnection with no appreciable guide field. The ecs is collocated with a layer of electron-scale electric fields normal to the ecs and pointing toward the ecs center plane. Both the observed electron and ion densities vary by more than a factor of 2 within one ion skin depth north and south of the ecs, and from the ecs into magnetic islands. Within each of the identified islands, there is a burst of supr...

The ISEE-3 Geotail Mission has extended our knowledge of the terrestrial magnetotail out to distances of 235 R e . This paper presents a review of the observations from this mission pertaining to the size, shape, and structure of the magnetotail. The data sets available include magnetic fields, electron plasma, electromagnetic waves, plasma composition, energetic ions (H, He, C, N, O) and electrons (2D), and energetic ion spectra in 3D. The observations show that the distant terrestrial magnetotail is similar to the the near-earth region, except that the predominant direction of flows is away from the earth. The shape becomes elliptical, with the major axis in the east-west direction. A semi-permanent X-line is deduced to be near 80 to 100 R e . A solar wind component is found in the ion compositions. Vortex-like events and magnetic flux ropes, both known from other missions, have also been found.

The distribution of energetic ion anisotropies in flux transfer events (FTEs) about the dayside magnetopause has been determined for ISEE 2 crossings of the boundary in 1977 and 1978. When the events are sorted according to the sign of the east-west component of the magnetic field in the magnetosphere, a clear correlation is observed on the northern morningside. When the field is eastward, particles flow antiparallel to the field, implying field line connection to the Northern Hemisphere; when the field is westward, the opposite is true. On the afternoonside, the particle anisotropies are correlated with latitude. Explanations for this pattern are discussed which involve FTE formation at low latitudes with subsequent motion at a velocity given by the vector superposition of the Alfven velocity from the release of magnetic tension and the magnetosheath bulk flow velocity. Evidence that the geomagnetic and not the geocentric solar magnetospheric equator is the source of FTEs is considered.

The September 8, 1978, crossing of the magnetopause by ISEE 1 and 2 has been studied in the light of energetic ion and electron data in order to derive the magnetic field topology. The plasma and magnetic field observations during this crossing provided evidence for the occurrence of plasma acceleration intrinsic to reconnection between interplanetary and magnetospheric magnetic field lines. The energetic particle observations result in two different pictures of the open and closed field lines within the magnetosphere, depending on either the ion or electron observations. According to the ion measurements, the high-speed flow can be placed exclusively on open field lines. The electrons, however, exhibit trapped distributions during these times. This apparent dilemma can be resolved by invoking magnetic mirroring of the electrons off the increased magnetosheath field, as shown in a companion paper by Daly and Fritz (1982).

Energetic electron (E greater than 20 keV) and ion (E greater than 25 keV) enhancements have been observed using the Isee 1 and 2 spacecraft during magnetic flux transfer events in the dayside magnetosheath just outside the magnetopause. The ions are seen to be streaming along the magnetic field, filling the 90-180 deg pitch angle region. The electrons are more isotropic and yet exhibit slight anisotropy in the direction opposite to that of the ions. From their intensities and spectra the ions appear to be of magnetospheric origin. With the interpretation of the flux transfer events as 'patchy' interconnection of magnetosheath and magnetospheric field lines, the ions are then seen to be previously trapped magnetospheric particles escaping along freshly opened field lines.

In a previous paper on the September 8, 1978, magnetopause crossing by the ISEE spacecraft, observations of trapped-like electron distributions coexisting with streaming ion distributions were reported. These observations were made for particles in the energy range >20 keV, inside the magnetopause, and near a possible reconnection event. In this paper we have investigated the idea that the electrons could be trapped by magnetic mirroring from the field in the magnetosheath. The loss cone angle predicted from the instantaneously measured magnetic field and the observed maximum field in the magnetosheath compares very favorably with the observed loss cone angles. The measured loss cone is always slightly wider than the predicted one, which can result from superimposing the magnetospheric source distribution onto the loss cone, but follows the magnetic field strength variations as the predicted value does. We argue that the ions are not similarly reflected because they fail to meet the adiabatic condition during the passage through the magnetopause. Having thus resolved the conflicting predictions about field line topology based on electrons and ions, we can be much more confident that the September 8, 1978, crossing of the magnetopause by ISEE is indeed a reconnection event.