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International audience; We report on six dipolarization fronts (DFs) embedded in fast earthward flows detected by the Magnetospheric Multiscale mission during asubstorm event on 23 July 2017. We analyzed Ohm’s law for each event and found that ions are mostly decoupled from the magnetic field byHall fields. However, the electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electrondecoupling at DF. We also analyzed the energy conversion process and found that the energy in the spacecraft frame is transferred from theelectromagnetic field to the plasma (J E > 0) ahead or at the DF, whereas it is the opposite (J E < 0) behind the front. This reversal ismainly due to a local reversal of the cross-tail current indicating a substructure of the DF. In the fluid frame, we found that the energy ismostly transferred from the plasma to the electromagnetic field (J E0 < 0) and should contribute to the deceleration of the fast flow.However, we show that the energy conversion process is not homogeneous at the electron scales due to electric field fluctuations likely relatedto lower-hybrid drift waves. Our results suggest that the role of DF in the global energy cycle of the magnetosphere still deserves more investigation. In particular, statistical studies on DF are required to be carried out with caution due to these electron scale substructures.

International audience

It is now well known that amplitude modulated HF transmissions into the ionosphere can be used to generate ELF/VLF signals using the so-called "electrojet antenna". Although most observations of the generated ELF/VLF signals have been made on the ground, several low and high-altitude satellite observations have also been reported (James et al., 1990). One of the important unknowns in the physics of ELF/VLF wave generation by ionospheric heating is the volume of the magnetosphere illuminated by the ELF/VLF waves. In an attempt to investigate this question further, ground-satellite conjunction experiments have recently been conducted using the four Cluster satellites and the HF heater of the High-Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska. Being located on largely closed field lines at L≈4.9, HAARP is currently also being used for ground-to-ground type of ELF/VLF wave-injection experiments, and will be increasingly used for this purpose as it is now being upgraded for higher power operation. In this paper, we describe the HAARP installation and present recent results of the HAARP-Cluster experiments. We give an overview of the detected ELF/VLF signals at Cluster, and a possible explanation of the spectral signature detected, as well as the determination of the location of the point of injection of the HAARP ELF/VLF signals into the magnetosphere using ray tracing.

The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (~50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ~46°. This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (~1 RE). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15–25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ~ 10) and a medium geomagnetic latitude (35° S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

The Cluster multi-point mission offers a unique collection of non-thermal continuum (NTC) radio waves observed in the 2–80 kHz frequency range over almost 15 years, from various view points over the radiating plasmasphere. Here we present rather infrequent case events, such as when primary electrostatic sources of such waves are embedded within the plasmapause boundary far from the magnetic equatorial plane. The spectral signature of the emitted electromagnetic waves is structured as a series of wide harmonic bands within the range covered by the step in plasma frequency encountered at the boundary. Developing the concept that the frequency distance df between harmonic bands measures the magnetic field magnitude B at the source (df = Fce, electron gyrofrequency), we analyse three selected events. The first one (studied in Grimald et al., 2008) presents electric field signatures observed by a Cluster constellation of small size (~ 200 to 1000 km spacecraft separation) placed in the vicinity of sources. The electric field frequency spectra display frequency peaks placed at frequencies fs = n df (n being an integer), with df of the order of Fce values encountered at the plasmapause by the spacecraft. The second event, taken from the Cluster tilt campaign, leads to a 3-D view of NTC waves ray path orientations and to a localization of a global source region at several Earth radii (RE) from Cluster (Décréau et al., 2013). The measured spectra present successive peaks placed at fs ~ (n+ 1/2) df. Next, considering if both situations might be two facets of the same phenomenon, we analyze a third event. The Cluster fleet, configured into a constellation of large size (~ 8000 to 25 000 km spacecraft separation), allows us to observe wide-banded NTC waves at different distances from their sources. Two new findings can be derived from our analysis. First, we point out that a large portion of the plasmasphere boundary layer, covering a large range of magnetic latitudes, is radiating radio waves. The radio waves are issued from multiple sources of small size, each related to a given fs series and radiating inside a beam of narrow cone angle, referred to as a beamlet. The beamlets illuminate different satellites simultaneously, at different characteristic fs values, according to the latitude at which the satellite is placed. Second, when an observing satellite moves away from its assumed source region (the plasmapause surface), it is illuminated by several beamlets, issued from nearby sources with characteristic fs values close to each other. The addition of radio waves blurs the spectra of the overall received electric field. It can move the signal peaks such that their position fs satisfiesfs = (n+α) df, with 0 < α < 1. These findings open new perspectives for the interpretation of NTC events displaying harmonic signatures.

Observations of equatorial magnetosonic waves made during the Cluster Inner Magnetospheric Campaign clearly show discrete spectra consisting of emissions around harmonics of the proton gyrofrequency. Equatorial magnetosonic waves are important because of their ability to efficiently scatter electrons in energy and pitch angle. This wave-particle interaction is numerically modeled through the use of diffusion coefficients, calculated based on a continuous spectrum such as that observed by spectrum analyzers. Using the Chirikov overlap resonance criterion, the calculation of the diffusion coefficient will be assessed to determine whether they should be calculated based on the discrete spectral features as opposed to a continuous spectrum. For the period studied, it is determined that the discrete nature of the waves does fulfill the Chirikov overlap criterion and so the use of quasi-linear theory with the assumption of a continuous frequency spectrum is valid for the calculation of diffusion coefficients.

l s’agit d’un patient de 53 ans presentant comme principaux antecedents, un diabete non insu-linodependant et une coronaropa-thie decouverte dans le cadre de la surveillance de son diabete, avec probable antecedent d’infarctus silencieux antero-septal, constatation d’une atteinte monotronculaire avec angioplastie de l’artere interventri-culaire anterieure et de la premiere diagonale en 2009 (Italie). Il est seden-taire, sans activite sportive reguliere ni autre facteur de risque cardiovascu-laire notable, notamment tabagique.Dans la prevision d’un projet de des-cente de la Vallee Blanche a ski (mas-sif du Mont-Blanc, France), il revoit son cardiologue traitant qui rea-lise un examen clinique et un elec-trocardiogramme (ECG) de repos, normaux. Il preconise la realisation d’un test non invasif de la reserve coronaire : realisation d’une echo-graphie de stress, sous dobutamine, sans anomalie retenue de la cine-tique segmentaire en dehors d’une hypokinesie antero-septale connue ne s’aggravant pas durant le test. Dans ces conditions, il est autorise a realiser ce projet.En cette fin mars 2013, la descente s’effectue par beau temps dans une neige lourde et profonde. Des le debut de la descente, le patient a des difficultes pour suivre le groupe ; il est asthenique, avec une sensa-tion de mal-etre, sans douleur thora-cique exprimee a l’entourage ou au guide. Il s’effondre a proximite du refuge du Requin (2516 m) lors de la remontee vers celui-ci. Un guide present, assiste de la gardienne du refuge debute les gestes qui sauvent et apporte le defibrillateur automa-tise externe (DAE) installe a l’annee dans ce refuge (programme d’equi-pement avec un financement de la Federation francaise de cardiologie, en collaboration avec l’Ifremmont et Pharefuge) (

The frequency range of the WHISPER relaxation sounder instrument on board CLUSTER, 4–80 kHz, has been chosen so as to encompass the electron gyro-frequency, Fce, and the electron plasma frequency, Fp, in most regions to be explored. Measurement of those frequencies, which are triggered as resonances by the sounder, provides a direct estimation of in situ fundamental plasma characteristics: electron density and magnetic field intensity. In the late mission phase, CLUSTER penetrated regions deep inside the plasmasphere where Fce and Fp are much higher than the upper frequency of the sounder's range. However, they are of the right order of magnitude as to place the lower hybrid frequency, Flh, in the 4–15 kHz band. This characteristic frequency, placed at a resonance of the medium, is triggered by the sounder's transmitter and shows up as an isolated peak in the received spectrum, not present in spectra of naturally occuring VLF waves. This paper illustrates, from analysis of case events, how measured Flh values give access to a plasma diagnostic novel of its kind. CLUSTER, travelling along its orbit, encounters favourable conditions where Fce is increasing and Fp decreasing, such that Fce/Fp increases from values below unity to values above unity. Measured Flh values thus give access, in turn, to the effective mass, Meff, indicative of plasma ion composition, and to the core plasmasphere electron density value, a parameter difficult to measure. The analysed case events indicate that the estimated quantities (Meff in the 1.0–1.4 range, Ne in the 5 × 102–104 cm−3 range) are varying with external factors (altitude, L value, geomagnetic activity) in a plausible way. Although covering only a restricted region (mid-latitude, low altitude inner plasmasphere), these measurements are available, since late 2009, for all CLUSTER perigee passes not affected by eclipses (on average, roughly a third of a total of ~200 passes per year) and offer multipoint observations previously unavailable in this region.

The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported.

The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported.

International audience; We have investigated the dependence of mass, energy, and charge of solar wind (SW) transport across Earth?s bow shock. An examination of 111 crossings during quiet SW in both quasi-perpendicular and quasi-parallel shock regions shows that 64 crossings had various degrees of heating and thermalization of SW. We found 22 crossings where the SW speed was

We present data from the sixth Cassini flyby of Titan (T5), showing that the magnetosphere of Saturn strongly interacts with the moon's ionosphere and exo-ionosphere. A simple electron ionisation model provides a reasonable agreement with the altitude structure of the ionosphere. Furthermore, we suggest that the dense and cold exo-ionosphere (from the exobase at 1430 km and outward to several Titan radii from the surface) can be explained by magnetospheric forcing and other transport processes whereas exospheric ionisation by impacting low energy electrons seems to play a minor role.

Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles have been derived from the electron plasma frequency identified by the WHISPER sounder supplemented, in-between soundings, by relative variations of the spacecraft potential measured by the electric field instrument EFW; ion velocity is also measured onboard these satellites. The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 RE every 10 min; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations of three plume events and compare CLUSTER in-situ data with global images of the plasmasphere obtained by IMAGE. In particular, we study the geometry and the orientation of plasmaspheric plumes by using four-point analysis methods. We compare several aspects of plume motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary as observed by the wave experiment WHISPER on the four spacecraft, (ii) drift velocity measured by the electron drift instrument EDI onboard CLUSTER and (iii) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.

The Cassini Radio and Plasma Wave Science (RPWS) Langmuir probe (LP) sensor observed the cold plasma environment around Titan during the first two flybys. The data show that conditions in Saturn's magnetosphere affect the structure and dynamics deep in the ionosphere of Titan. The maximum measured ionospheric electron number density reached 3800 per cubic centimeter near closest approach, and a complex chemistry was indicated. The electron temperature profiles are consistent with electron heat conduction from the hotter Titan wake. The ionospheric escape flux was estimated to be 10 25 ions per second.

We present observations of plasma density structures crossed by the CLUSTER spacecraft constellation near orbit perigee, with the spacecraft located in the vicinity of the plasmapause boundary. Although the constellation is not arranged as a perfect tetrahedron, the four-point measurements reveal interesting properties of density structures, unknown before the four-points in situ observations from the CLUSTER mission. The set of plasma density profiles shown are derived from the EFW and WHISPER instruments observations in the dusk sector of the plasmasphere region. They yield new insights into: (i) comparative along and cross-field dimensions; (ii) the dynamics of small-scale structures. They illustrate the great opportunity offered by the CLUSTER mission to resolve new challenges in magnetospheric physics, including a clearer understanding of the physics involved in the dynamics of the plasmasphere and the formation of its outer boundary: the plasmapause. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

The electron density profiles derived from the EFW and WHISPER instruments on board the four Cluster spacecraft reveal density structures inside the plasmasphere and at its outer boundary, the plasmapause. We have conducted a statistical study to characterize these density structures. We focus on the plasmasphere crossing on 11 April 2002, during which Cluster observed several density irregularities inside the plasmasphere, as well as a plasmaspheric plume. We derive the density gradient vectors from simultaneous density measurements by the four spacecraft. We also determine the normal velocity of the boundaries of the plume and of the irregularities from the time delays between those boundaries in the four individual density profiles, assuming they are planar. These new observations yield novel insights about the occurrence of density irregularities, their geometry and their dynamics. These in-situ measurements are compared with global images of the plasmasphere from the EUV imager on board the IMAGE satellite.

The Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation, WHISPER, performs high frequency electric field measurements on the four satellites of the CLUSTER mission. In active mode, the WHISPER behaves like a classical topside sounder. It provides, via the identification of resonances that are excited at characteristic frequencies of the encountered plasmas reliable and accurate determination of the total electron density and magnetic field strength. Whenever the transmitter is switched off, the WHISPER becomes a simple wave receiver (passive mode). The 2 to 80 kHz frequency range of the electric component of natural waves is then monitored. The main objective of the presentation is to highlight the plasma and natural waves diagnosis capabilities of the WHISPER instrument. The way the plasma resonances are extracted and identified is pointed out and results obtained from the solar wind down to the Earth's plasmasphere are shown.

The WHISPER relaxation sounder that is onboard the four CLUSTER spacecraft has as its main scientific objectives to monitor the natural waves in the 2 kHz–80 kHz frequency range and, mostly, to determine the total plasma density from the solar wind down to the Earth's plasmasphere. To fulfill these objectives, the WHISPER uses the two long double sphere antennae of the Electric Field and Wave experiment as transmitting and receiving sensors. In its active working mode, the WHISPER works according to principles that have been worked out for topside sounding. A radio wave transmitter sends an almost monochromatic and short wave train. A few milliseconds after, a receiver listens to the surrounding plasma response. Strong and long lasting echoes are actually received whenever the transmitting frequencies coincide with characteristic plasma frequencies. Provided that these echoes, also called resonances, may be identified, the WHISPER relaxation sounder becomes a reliable and powerful tool for plasma diagnosis. When the transmitter is off, the WHISPER behaves like a passive receiver, allowing natural waves to be monitored. This paper aims mainly at the resonance identification process description and the WHISPER capabilities and performance highlighting.

International audience; Magnetosonic waves are commonly observed in the vicinity of the terrestrial magnetic equator. It has been proposed that within this region they may interact with radiation belt electrons, accelerating some to high energies. These wave-particle interactions depend upon the characteristic properties of the wave mode. Hence, determination of the wave properties is a fundamental part of understanding these interaction processes. Using data collected during the Cluster Inner Magnetosphere Campaign, this paper identifies an occurrence of magnetosonic waves, discusses their generation and propagation properties from a theoretical perspective, and utilizes multispacecraft measurements to experimentally determine their dispersion relation. Their experimental dispersion is found to be in accordance with that based on cold plasma theory.

International audience; Cluster multipoint measurements are used to study two successive magnetosheath flux transfer events (FTEs). Magnetic field lines in the leading region are found to be closed magnetospheric field lines. For event 1 these field lines are wounded up by a large current structure oriented eastward and moving poleward. Conversely, the trailing region corresponds to opened magnetic field lines. For both events the leading edge of the FTEs is a tangential discontinuity separating the magnetosheath from closed field lines. In the case of event 1 magnetosheath ions are accelerated through the FTE trailing edge via a rotational discontinuity and penetrate on closed field lines through a second discontinuity. Thus, the ion jet is accelerated equatorward of the spacecraft but the backtracking of the discontinuities and the lack of dispersion show that ion acceleration occurs at less than 2 RE from Cluster. On the other hand the extrapolation forward indicates that the FTE bulge steepens as in simulations of Dorelli and Bhattacharjee). Evidence is given for the penetration of magnetosheath ions inside the core of the FTE, on closed field lines. Magnetosheath electrons are accelerated in parallel and antiparallel directions on open and on closed field lines, thus breaking the frozen-in condition. Event 2 is also split in two distinct regions but no evidence is found for accelerated bidirectional magnetosheath electrons. For event 2 the two discontinuities at the trailing region are stacked together when they are crossed by the spacecraft, suggesting that the current splitting is a reconnection signature.

International audience; Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.

On August 18, 1999, the Cassini spacecraft flew by Earth at an altitude of 1186 km on its way to Saturn. Although the flyby was performed exclusively to provide the spacecraft with sufficient velocity to get to Saturn, the radio and plasma wave science (RPWS) instrument, along with several others, was operated to gain valuable calibration data and to validate the operation of a number of capabilities. In addition, an opportunity to study the terrestrial radio and plasma wave environment with a highly capable instrument on a swift fly-through of the magnetosphere was afforded by the encounter. This paper provides an overview of the RPWS observations at Earth, including the identification of a number of magnetospheric plasma wave modes, an accurate measurement of the plasma density over a significant portion of the trajectory using the natural wave spectrum in addition to a relaxation sounder and Langmuir probe, the detection of natural and human-produced radio emissions, and the validation of the capability to measure the wave normal angle and Poynting flux of whistler-mode chorus emissions. The results include the observation of a double-banded structure at closest approach including a band of Cerenkov emission bounded by electron plasma and upper hybrid frequencies and an electron cyclotron harmonic band just above the second harmonic of the electron cyclotron frequency. In the near-Earth plasma sheet, evidence for electron phase space holes is observed, similar to those first reported by Geotail in the magnetotail. The wave normal analysis confirms the Polar result that chorus is generated very close to the magnetic equator and propagates to higher latitudes. The integrated power flux of auroral kilometric radiation is also used to identify a series of substorms observed during the outbound passage through the magnetotail.

Cassini plasma wave and particle observations are combined with magnetometer measurements to study Titan´s induced magnetic tail. In this study, we report and analyze the plasma acceleration in Titan´s induced magnetotail observed in flybys T17, T19, and T40. Radio and Plasma Wave Science observations show regions of cold plasma with electron densities between 0.1 and a few tens of electrons per cubic centimeter. The Cassini Plasma Spectrometer (CAPS)-ion mass spectrometer (IMS) measurements suggest that ionospheric plasma in this region is composed of ions with masses ranging from 15 to 17 amu and from 28 to 31 amu. From these measurements, we determine the bulk velocity of the plasma and the Alfvén velocity in Titan's tail region. Finally, a Walén test of such measurements suggest that the progressive acceleration of the ionospheric plasma shown by CAPS can be interpreted in terms of magnetic tension forces. Fil: Romanelli, Norberto Julio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Modolo, R.. Latmos; Francia Fil: Dubinin, E.. Max Planck Institut; Alemania Fil: Berthelier, J. J.. Latmos; Francia Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Wahlund, J. E.. Swedish Institute Of Space Physics; Suecia Fil: Leblanc, F.. Latmos; Francia Fil: Canu, P.. Ecole Polytechnique; Francia Fil: Edberg, N. J. T.. Swedish Institute Of Space Physics; Suecia Fil: Waite, H.. Southwest Research Institute; Estados Unidos Fil: Kurth, W. S.. University of Iowa; Estados Unidos Fil: Gurnett, D.. University of Iowa; Estados Unidos Fil: Coates, A.. University College London; Estados Unidos Fil: Dougherty, M.. Imperial College London; Reino Unido

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks as observed by the Ulysses spacecraft. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions (EDF) in the energy range 1.6 to 862 eV measured by the spacecraft, we compute the wave growth rate of the electromagnetic electron cyclotron and Landau instabilities for the case of oblique propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows mostly downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations.

The WHISPER sounder on the Cluster spacecraft is primarily designed to provide an absolute measurement of the total plasma density within the range 0.2–80 cm-3. This is achieved by means of a resonance sounding technique which has already proved successful in the regions to be explored. The wave analysis function of the instrument is provided by FFT calculation. Compared with the swept frequency wave analysis of previous sounders, this technique has several new capabilities. In particular, when used for natural wave measurements (which cover here the 2–80 kHz range), it offers a flexible trade-off between time and frequency resolutions. In the basic nominal operational mode, the density is measured every 28 s, the frequency and time resolution for the wave measurements are about 600 Hz and 2.2 s, respectively. Better resolutions can be obtained, especially when the spacecraft telemetry is in burst mode. Special attention has been paid to the coordination of WHISPER operations with the wave instruments, as well as with the low-energy particle counters. When operated from the multi-spacecraft Cluster, the WHISPER instrument is expected to contribute in particular to the study of plasma waves in the electron foreshock and solar wind, to investigations about small-scale structures via density and high-frequency emission signatures, and to the analysis of the non-thermal continuum in the magnetosphere.

International audience; The main part of Cluster Spatio Temporal Analysis of Field Fluctuations (STAFF) experiment consists of triaxial search coils allowing the measurements of the three magnetic components of the waves from 0.1 Hz up to 4 kHz. Two sets of data are produced, one by a module to filter and transmit the corresponding waveform up to either 10 or 180 Hz (STAFF-SC) and the second by an onboard Spectrum Analyser (STAFF-SA) to compute the elements of the spectral matrix for five components of the waves, 3 × B and 2 × E (from EFW experiment) in the frequency range 8 Hz to 4 kHz. In order to understand the way the output signal of the search coils are calibrated, the transfer functions of the different parts of the instrument are described as well as the way to transform telemetry data into physical units, across various coordinate systems from the spinning sensors to a fixed and known frame. The instrument sensitivity is discussed. Cross-calibration inside STAFF (SC and SA) is presented. Results of cross-calibration between the STAFF search coils and the Cluster Flux Gate Magnetometer (FGM) data are discussed. It is shown that these cross-calibrations lead to an agreement between both data sets at low frequency within a 2% error. By means of statistics done over 10 yr, it is shown that the functionalities and characteristics of both instruments have not changed during this period.

International audience; Shock waves are widespread in collisionless space plasmas throughout the Universe. How particles are accelerated at these shocks has been the subject of much research attention. The dominant source of the high-energy particles that pervade our Galaxy (cosmic rays) is thought to be the high-Mach number collisionless shocks that form around young supernova remnants, but it is unclear how much the lower Mach number collisionless shock waves frequently encountered by spacecraft in Solar System space plasmas can tell us about particle acceleration in the higher Mach number regime. Here we review recent studies of the shock wave that stands in the solar wind in front of the planet Saturn (Saturn's bow shock), based on Cassini spacecraft observations. This review represents a new direction of shock physics research, with the potential to bridge the gap between Solar System and astrophysical shocks. These studies have confirmed that Saturn's bow shock is one of the strongest shocks in the Solar System, and a recent discovery indicates that electron acceleration at high-Mach numbers may occur irrespective of the upstream magnetic field geometry. This is important because astrophysical shocks can often only be studied remotely via emissions associated with accelerated electrons. We discuss possible future directions of this emerging sub-field of collisionless space plasma shock physics.

International audience; Two of the many features associated with nonlinear upstream structures are (1) the solar wind (SW) mean flow slows down and deviates substantially and (2) the temperature of the plasma increases in the structure. In this Letter, we show that the SW beam can be present throughout the entire upstream event maintaining a nearly constant beam velocity and temperature. The decrease of the velocity is due to the appearance of new particles moving in the opposite direction that act against the SW beam and reduce the mean velocity as computed via moments. The new population, which occupies a larger velocity space, also contributes to the second moment, increasing the temperature. The new particles include the reflected SW beam at the bow shock and another population of lower energies, accelerated nearby at the shock or at the boundary of the nonlinear structures.

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks in and out of the ecliptic plane, as observed by the Ulysses spacecraft. We focus here on one shock in the ecliptic plane as a reference and three shocks obtained at −30, −54 and −55.4 degrees of heliographic latitude respectively. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions in the energy range 1.6 to 862 eV, we compute the temperature anisotropy and the wave growth rate of the electromagnetic electron cyclotron instability for the case of parallel propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows only downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations. Broadening of the wave reduced frequency range of the instability and an increase of the temperature anisotropy with latitude are observed.

There is evidence that mast cells and their degranulation products are involved in resistance against tumours. Previously, we have shown that tumour incidence and growth were inversely correlated with basal histamine levels, i.e. mast cell numbers, in tissues of W/Wv (mast cell-deficient), Wv/+ (partially mast cell-depleted), and +/+ (mast cell-sufficient) mice, and that histamine levels were increased in numerous tissues of tumour-bearing animals, including C57BL/6 and C3H mice, Sprague-Dawley and Commentry rats. The aim of this work was to analyse the incidence and growth of a grafted tumour (fibrosarcoma MC-B6-1) in W/+ mice, as compared with W/Wv, Wv/+ and +/+ mice, and to study the modifications in tissue histamine levels in W/+, W/Wv, Wv/+ and +/+ tumour-grafted mice, in order to determine whether or not these modifications were correlated with resistance to tumours. We report confirmation that tumour incidence and growth are inversely correlated with basal tissue histamine levels in W/Wv, Wv/+, and +/+ fibrosarcoma-bearing mice. However, in W/+ mice (normal tissue histamine levels), tumour incidence was the same as in Wv/+ mice. Histamine levels in tissues of W/Wv, Wv/+, W/+ and +/+ tumour bearing mice were not significantly different from those in controls. They were higher in some tissues of Wv/+ mice rejecting the tumour than in Wv/+ mice not rejecting the tumour. However, in W/+ and +/+ mice, histamine levels were not significantly different, and even tended to be lower in most tissues of mice rejecting the tumour than in mice accepting the tumour. Overall, these results suggest that resistance to tumours cannot be ascribed solely to mast cells, and that other mechanisms may also be involved. Thus, further experiments are needed to clarify the exact role of mast cells and mast cell-derived mediators and cytokines in the defence against tumours.

International audience; The four WHISPER instruments, part of the Wave Experiment Consortium on board the multi satellite CLUSTER mission, include each a relaxation sounder aimed to measure with a good precision and reliability the frequency positions of F p , electron plasma frequency, and of F ce , electron gyro-frequency. Those quantities give access to electron density and intensity of magnetic field, key parameters defining local plasma regime. WHISPER sounder's design and realization, based on the expertise provided by successful missions operated in late seventies and eighties (GEOS, ISEE, Viking), is characterized by use of a processor devoted to on board frequency analysis via FFT. This choice makes those relaxation sounders unique of their kind, allowing in particular a complete plasma diagnostic to be made in only 1.5 s, almost one order of magnitude faster than in the past. The CLUSTER mission itself is unique, by its multi-point capability, and by its orbit, which along the mission allowed exploring a large variety of key regions of the magnetosphere. We present in this paper a few examples of WHISPER instrument behaviour and results, exploring in particular magnetosheath, polar cap, outer and inner plasmasphere. In the latter region, F p and F ce frequency values are far above the working frequency range of the instrument. This range, however, includes the lower hybrid frequency, F lh , which shows up as a clear resonance triggered by the sounder, and allows measurement of Ne whenever F p /F ce

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The aurorae are dynamic, luminous displays that grace the night skies of Earth’s high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth’s atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The “ideal magnetohydrodynamics” description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfvén concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.

International audience; Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the $k$-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross- Scale mission.

Turbulence at MagnetoHydroDynamics (MHD) scales in the solar wind has been studied for more than three decades, using data analysis, theoretical and numerical modeling. However, smaller scales have not been explored until very recently. Here, we review recent results on the first observation of cascade and dissipation of the solar wind turbulence at the electron scales. Thanks to the high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectra of turbulence up to ∼ 100 Hz (in the spacecraft reference frame) and found evidence of energy dissipation around the Doppler-shifted electron gyroscale f ρ e . Before its dissipation, the energy is shown to undergo two cascades: a Kolmogorov-like cascade with a scaling f − 1.6 above the proton gyroscale, and a new f − 2.3 cascade at the sub-proton and electron gyroscales. Above f ρ e the spectrum has a steeper power law ∼ f − 4.1 down to the noise level of the instrument. Solving numerically the linear Maxwell–Vlasov equations combined with recent theoretical predictions of the Gyro-Kinetic theory, we show that the present results are consistent with a scenario of a quasi-two-dimensional cascade into Kinetic Alfven modes (KAW). New analyses of other data sets, where the Cluster separation (of about ∼ 200 km ) allowed us to explore the sub-proton scales using the k-filtering technique, and to confirm the 2D nature of the turbulence at those scales.

Data acquired during several multiday periods in 1982 at ground stations Siple, Halley, and Kerguelen and on satellites Dynamics Explorer 1, International Sun Earth Explorer 1, and GEOS 2 have been used to investigate thermal plasma structure and dynamics in the duskside plasmasphere bulge region of the Earth. The distribution of thermal plasma in the dusk bulge sector is difficult to describe realistically, in part because of the time integral manner in which the thermal plasma distribution depends upon on the effects of bulk cross-B flow and interchange plasma flows along B. While relatively simple MHD models can be useful for qualitatively predicting certain effects of enhanced convection on a quiet plasmasphere, such as an initial sunward entrainment of the outer regions, they are of limited value in predicting the duskside thermal plasma structures that are observed. Furthermore, use of such models can be misleading if one fails to realize that they do not address the question of the formation of the steep plasmapause profile or provide for a possible role of instabilities or other irreversible processes in plasmapause formation. Our specific findings, which are based both upon the present case studies and upon earlier work, include the following: (1) during active periods the plasmasphere appears to become divided into two entities, a main plasmasphere and a duskside bulge region. (2) in the aftermath of an increase in convection activity, the main plasmasphere tends (from a statistical point of view) to become roughly circular in equatorial cross section, with only a slight bulge at dusk; (3) the abrupt westward edge of the duskside bulge observed from whistlers represents a state in the evolution of sunward extending streamers; (4) in the aftermath of a weak magnetic storm, 10 to 30% of the plasma 'removed' from the outer plasmasphere appears to remain in the afternoon-dusk sector beyond the main plasmasphere. (5) outlying dense plasma structures may circulate in the outer duskside magetosphere for many days following an increase in convection, unless there is extremely deep quieting; (6) a day-night plasmatrough boundary may be identified in equatorial satellite data; (7) factor-of-2-to-10 density irregularities appear near the plasmatrough from the ionosphere at L = 4.6, predominantly bidirectional field aligned and equatorially trapped light ion pitch angle distributions give away to a predominantly isotropic distribution (as seen by DE 1) when the plasma density reaches a level a factor of about 3 below the satured plasmasphere level; (9) some outlying dense plasma structures are effectively detached from the main plasmasphere, while others appear to be connected to that body.

The Ulysses spacecraft encountered the planet Jupiter in February 1992, on its journey towards high heliospheric latitude. During the approach to the planet, as well as on the outbound pass, while receding from the Jovian bow shock, the Plasma Frequency Receiver that is part of the Unified Radio and Plasma Wave experiment (URAP) recorded bursts of plasma waves in the frequency range of a few kHz. These emissions, first observed by the PWS experiment onboard the Voyager spacecraft, have been identified as upstream electron plasma waves. In this paper, we present the first analysis of the characteristics of these emissions, which are very similar to those found in the Earth's electron foreshock, upstream of the Earth's bow shock. These bursty emissions, with a peak frequency very close to the local electron plasma frequency Fpe, have a typical electric field amplitude in the range 0.01–0.1 mV m−1, with some bursts above 1 mV m−1. The frequency bandwidth over which significant power can be found above the instrument background noise ranges from below 0.2 Fpc to about 2 Fpc. On the basis of our present knowledge of similar emissions observed at Earth, we suggest that the broadband emissions are triggered by suprathermal (a few tens of eV) electrons, streaming back from Jupiter's bow shock.

The electron analyzer of the solar wind plasma experiment aboard the Ulysses spacecraft measured the plasma properties of the Jovian magnetosphere and surrounding regions during the February 1992 encounter with Jupiter. In addition to sampling a new region of the Jovian magnetosphere, the Ulysses electron measurements were unique in that they included fine directional sampling over nearly 4π sr in look direction, for electron energies up to 862 eV. In this paper we present an overview of electron bulk parameters and a sampling of distribution shapes for the magnetosphere and adjacent plasma regions. The magnetopause was crossed 10 times, with each crossing characterized by a boundary layer with mixed magnetospheric and magnetosheath-like electron distributions. The spacecraft transited the dayside, prenoon, equatorial magnetosphere inbound, and the near-terminator, dusk magnetosphere at mid-latitudes outbound. The middle and inner magnetosphere contained a distinct plasma sheet, well-ordered in magnetic latitude, while the outer magnetosphere was less cleanly structured. Field-aligned electron anisotropies were observed throughout the magnetosphere. Unique electron spectra were seen in probable open-field line regions at the highest sampled magnetic latitudes in the inner magnetosphere. Azimuthal flow velocities indicated significant departures from rigid corotation, perhaps representing a combination of corotation and tailward flow. Radial plasma flows were slightly outward in the prenoon plasma sheet and strongly outward throughout the dusk terminator region, but were inward at higher latitudes on the dayside. Strong southward flows were observed in the outer magnetosphere on the dusk side.

The spacecraft Ulysses flew through the Jovian magnetosphere during February 1992. This paper compares the magnetic field observations recorded during the inbound pass of the flyby with the electron density as derived from the URAP instrument. In general, it is expected that the density variations will anti-correlate with the magnetic field strength in order to maintain pressure balance, although there may be instances when a temperature or energy rise alone could balance the static stress. Furthermore, there is the possibility that a dynamic process could occur which would cause both the density and field magnitude to rise in unison. In the middle magnetosphere, anti-correlation is found to exist between the two data sets; however, in the outer magnetosphere (which was characterized by very disturbed fields) and in the transition region between the outer and middle magnetospheres, there is no simple relationship between the density and field. Examples of anti-correlation, temperature or energy increases and dynamic processes are found.

During the Ulysses flyby of Jupiter, a whistler-mode emission was periodically detected by the unified Radio and Plasma wave (URAP) experiment during intervals when the spacecraft extended to high magnetic latitudes. The signal was detected between the local electron plasma frequency and lower hybrid resonance and appears as a funnel-shaped structure on frequency-versus-time spectrograms; these characteristics are very reminiscent of whistler-mode auroral hiss observed at high latitudes at Earth. Ray tracing of the emission occurrences suggests the emission source is on magnetic field lines extending out to at least 65 R(sub J). This location associates the emission with the boundary between open and closed field lines -- not the Io torus. The emission radiates about 10(exp 7) W of power. Consequently, the auroral input power derived from the solar wind to drive the emission is believed to be 10(exp 10-12) W (or about 1% of the energy associated with Io torus electrical processes).

International audience; We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfve´n waves with !plas 0:1!ci down to k?i 2. Each k spectrum in the direction perpendicular to B0 shows two scaling ranges separated by a breakpoint (in the interval ½0:4; 1k?i): a Kolmogorov scaling k1:7 ? followed by a steeper scaling k4:5 ? . We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate.

[1] We investigate the excellent correlation between ionospheric upgoing electron beams and broadband electrostatic emissions (0-6 kHz) observed by Cluster, at ~5 to 9 Earth's radii above the polar cap. In the absence of detailed, high time resolution waveform data in that region, we precisely analyzed several electron beams to obtain information concerning wave-particle interactions. Our results indicate that these beams are extremely variable and occasionally show multiple components. The processes involved might then occur on very short time scales, of the order of or shorter than sampling rates, typically 100 ms. We suggest that non linearities are at the origin of the spread of the frequency range of the waves simultaneously observed, as well as of the beam variability. We conclude that these electron beams are likely to destabilize Langmuir waves and, by the non-linear evolution of the electron bump-on-tail instability, could be responsible for the appearance of electrostatic solitary waves above the polar cap.

The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of aurorallike hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the lo plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the lo torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.