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We present observations of "lion roars" obtained in the magnetosheath by the Spectrum Analyser (SA) of the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment aboard Cluster. STAFF-SA calculates, in near real time, the complete auto- and cross-spectral matrix derived from three magnetic and two electric components of the electromagnetic field at 27 frequencies in the range of 8 Hz to 4 kHz. This allows the study of the properties of whistler mode waves and more particularly, the properties of "lion roars", which are intense, short-duration, narrow-banded packets of whistler waves. Their presence is favoured by the magnetic field troughs associated with mirror mode structures. During two short periods of well-defined mirror modes, we study the depth δB/B of the magnetic troughs, and the direction of propagation of the lion roars. During the first period, close to the magnetopause, deep magnetic troughs pass the satellites. Lion roars are then observed to propagate simultaneously in two directions, roughly parallel and anti-parallel to the magnetic field: this probably indicates that during this period, the satellites were within the successive source regions of lion roars. For the second period, far from the magnetopause, the magnetic troughs are less deep. Lion roars are propagating in only one direction, roughly anti-parallel to the magnetic field, suggesting that the source regions are more distant and predominantly on one side of the satellites.Key words. Magnetospheric physics (magnetosheath; plasma waves and instabilities) Radio science (radiowave propagation)

For the first time the evolution of interplanetary rotational discontinuities (RDs) are observed in the solar wind, in the magnetosheath and in the dayside magnetosphere by the ISEE 1-2-3 spacecraft. Interaction of a RD with the bow shock builds up a transient density event (TDE) in the magnetosheath, displaying two density peaks anticorrelated to the magnetic field modulus. TDEs are convected from the bow shock to the dayside magnetopause without spreading. The duration of a TDE is around 15 s and two close TDEs can merge in a single structure. The density in a TDE exceeds the surrounding level by a factor of about 35%, while the field modulus can decrease by a large amount. The interaction of a TDE with the magnetopause is analyzed in terms of impulsive penetration process. The element of plasma injected in the magnetosphere is filamentary, its signature is different from the signature of a flux transfer event or a surface wave.

The ISEE radio wave propagation electron density experiment allowed the determination of the integrated electron density between the ISEE 1 and ISEE 2 satellites at the relatively high rate of 8 or 32 Hz. When the component of the spacecraft separation vector in the direction of the normal to the magnetopause is significantly smaller than the thickness of the current layer, this data set allows the internal structure of the magnetopause to be studied and compared with theoretical predictions. For a particular triple subsolar magnetopause crossing with high magnetic shear, an electron density overshoot is observed in the current layer adjacent to the magnetosheath. The similarity of the three crossings indicates that the internal structure of the magnetopause does not change dramatically during the time interval considered. A superposed epoch analysis of these crossings is consistent with the density profile obtained from kinetic simulations. The general relationship between magnetic field asymmetry, magnetic field rotation angle and electron density overshoot is discussed. It is concluded that a density overshoot could be a typical feature of the subsolar magnetopause with high magnetic shear. This conclusion is supported by two other dayside magnetopause crossings for which high time resolution electron density data are available.

International audience; Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth's magnetosheath, the ISEE 1-2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ? 0.5 – 4 × 10–9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to1RE) just downstream of the shock ramp, and close to the magnetopause.

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 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.

The radio receiver of the Unified Radio and Plasma experiment aboard the Ulysses spacecraft records spectra of the quasi-thermal plasma noise. The interpretation of these spectra allows the determination of the total electron density Ne and of the cold (core) electron temperature Tc in the solar wind. A single power law does not fit the variations of Ne which result from the contribution from different solar wind structures. The distribution of the values of Tc suggests that, on the average, the solar wind is nearly isothermal.

ISEE1 and 2 high resolution electron density and magnetic field measurements have been used to study characteristic structures, identified as FTEs, observed inside the magnetosphere close to the magnetopause. We investigate new properties: a volcano-like signature in the magnetic field strength, a thin sheet structure at the leading edge, and a wake. The plasma compressibility is analysed through the structure. Auto and cross spectral analysis of the data reveal the signature of compressive modes in the wake of the FTE.

[1] On June 30, 2001, around 0530 UT, Cluster was moving along the magnetopause with spacecraft on both sides of the discontinuity. The configuration was ‘quasi-ideal’ with magnetic field and plasma flow almost aligned in the magnetosheath and nearly anti-parallel to the magnetospheric field. Cluster observed several perturbations with leading and trailing edges corresponding respectively to tangential and rotational discontinuities. They present a complex 3D topology, consistent with the inter-linking of flux tubes resulting from reconnections occurring at different sites.

One of the objectives of the Cluster mission is to study sources of various electromagnetic waves using the four satellites. This paper describes the methods we have applied to data recorded from the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. This spectral matrix is analysed to determine, for each satellite, the direction of the wave normal relative to the Earth’s magnetic field as a function of frequency and of time. Due to the Cluster orbit, chorus emissions are often observed close to perigee, and the data analysis determines the direction of these waves. Three events observed during different levels of magnetic activity are reported. It is shown that the component of the Poynting vector parallel to the magnetic field changes its sense when the satellites cross the magnetic equator, which indicates that the chorus waves propagate away from the equator. Detailed analysis indicates that the source is located in close vicinity of the plane of the geomagnetic equator. Key words. Magnetospheric physics (plasma waves and instabilities; storms and substorms); Space plasma physics (waves and instabilities)

In this paper we present an analysis of the satellite current-voltage (I-V) characteristics observed during the TSS-IR mission. The satellite I-V curves were compared with the predictions by two theoretical models: the first one [Parker and Murphy, 1967] considers the channeling effect of the terrestrial magnetic field as the dominating process in the current collection, whereas the second one [Alpert et al., 1965] neglects the magnetic field and assumes an isotropic spherical geometry. Even though neither of the two theories reproduces rigorously the TSS experimental situation, as they neglect both the motion of the body and possible anomalous collisions, we find that both the models, in certain conditions, could reproduce theoretical curves in agreement with the data. However we suggest that, when the effect of the plasma turbulence is considered, the data could be better interpreted on the basis of the Alpert formulation.

Ulysses spacecraft radio and plasma wave observations indicate that some variations in the intensity and occurrence rate of electric and magnetic wave events are functions of heliographic latitude, distance from the sun, and phase of the solar cycle. At high heliographic latitudes, solartype Ill radio emissions did not descend to the local plasma frequency, in contrast to the emission frequencies of some bursts observed in the ecliptic. Short-duration bursts of electrostatic and electromagnetic waves were often found in association with depressions in magnetic field amplitude, known as magnetic holes. Extensive wave activity observed in magnetic clouds may exist because of unusually large electron-ion temperature ratios. The lower number of intense in situ wave events at high latitudes was likely due to the decreased variability of the high- latitude solar wind.

There have been many reports of the terrestrial foreshock as a source of freely propagating electromagnetic (e.m.) radiation1–7, identified as plasma emission at twice the solar-wind plasma frequency, 2fp. The 2fp source is close behind the curved surface defined by the interplanetary magnetic field lines tangent to the Earth's bow shock. Electrons accelerated at the shock over a wide range of energies propagate along these field lines where, from a time-of-flight effect6, they have a distribution that is unstable to the production of Langmuir waves6,8. These Langmuir waves9,10 and the unstable electron distributions11,12 have been observed. The mechanism suggested for generating the 2fp radiation5,6,13,14 by the terrestrial foreshock is closely related to present models of type III solar radio emission and rely on some of the energy in the Langmuir waves converting to e.m. waves. The e.m. emission of type III bursts is known to be produced in the solar wind at both the fundamental and second harmonic15, and whether fundamental emission is produced in the terrestrial foreshock is of considerable interest. Comparison of nearby fundamental and harmonic emissions and the Langmuir wave energy density in the source will help discriminate between the different conversion models8,14,16. We present here unambiguous measurements made with the sounder experiment aboard the International Sun–Earth Explorer-1 (ISEE-1) and the radio experiment on ISEE-3 of simultaneous fundamental and second harmonic e.m. emission from the Earth's foreshock.

Data from three ISEE experiments has been analyzed during several periods of turbulence observed in the solar wind upstream of the earth's quasi-parallel bow shock. Radio observations are used to validate a shock model, which is subsequently used to compute various geometrical parameters during all the periods studied. One typical 9-hour period on November 4, 1977, is discussed in some detail to illustrate the parameters studied and the correlations found. It is shown that during this period, the radio noise spectrum has two components, one centered around the local electron plasma frequency and the other at somewhat lower frequencies; the latter component has a shorter wavelength and correlates with the level of MHD turbulence. A multivariate canonical statistical analysis of particle and MHD data during a 2-week period shows that the proton anisotropy and turbulence level correlate well with the minimum backstreaming proton parallel velocity pmin which, as defined here, is a purely geometrical parameter. Trivariate analysis shows that the correlation of particles and turbulence with the angle between the magnetic field and the shock normal have their sense reversed when allowance is made for the strong correlations with pmin. A very good correlation has been found between power and compressibility in magnetic fluctuations.

We have performed auto and cross spectral analysis of the electron density and vector magnetic field fluctuations recorded aboard ISEE 1 and 2 in the magnetosheath close the Earth's bow shock when in quasiperpendicular configuration. The analysis shows the characteristic signatures of mirror type modes downstream of the undershoot of the shock. copyright American Geophysical Union 1989

The French electron density experiment aboard the ISEE 1 and 2 satellites really consists of two separate, but complementary, experiments to measure the total electron density by means of radio techniques. Both experiments are new: one flew above the ionosphere for the first time on the satellite GEOS, launched in April 1977, while the other takes advantage of the unique ISEE feature of having two spacecraft which are always relatively close together. The principles and the realization of both experiments are described.

Plasma, electric-field and magnetic-field data from several experiments on board the spacecraft ISEE 1 and 2 have been analysed in the interaction region upstream of the Earth's bow shock. Upstream waves which are known to be associated with diffuse distributions of backstreaming protons are shown to correlate also with variability in the distribution of the incoming solar-wind protons. Both phenomena are also clearly connected with the presence of enhanced electric-field turbulence. On the basis of these relations, a preliminary discussion can be given of the complex nonlinear plasma processes occurring in the foreshock region.

The receiver in the satellite UK-2 is briefly described. Interference-free data received where the satellite is near the apogee of its orbit is of interest for astronomical and ionospheric work, and typical samples of such data are shown, the salient features being pointed out. Among the tatter are the ionospheric noise bands, and the propagation of waves in the i-mode. The method of determination of the orientation of the satellite at any given time is described, and the consequent conclusions about the polarisation of the signals are stated.

We analyse the fluctuations of the electron density and of the magnetic field in the Earth's magnetosheath to identify the waves observed below the proton gyrofrequency. We consider two quiet magnetosheath crossings i.e. 2 days characterized by small-amplitude waves, for which the solar wind dynamic pressure was low. On 2 August 1978 the spacecraft were in the outer magnetosheath. We compare the properties of the observed narrow-band waves with those of the unstable linear wave modes calculated for an homogeneous plasma with Maxwellian electron and bi-Maxwellian (anisotropic) proton and alpha particle distributions. The Alfvén ion cyclotron (AIC) mode appears to be dominant in the data, but there are also density fluctuations nearly in phase with the magnetic fluctuations parallel to the magnetic field. Such a phase relation can be explained neither by the presence of a proton or helium AIC mode nor by the presence of a fast mode in a bi-Maxwellian plasma. We invoke the presence of the helium cut-off mode which is marginally stable in a bi-Maxwellian plasma with α particles: the observed phase relation could be due to a hybrid mode (proton AIC+helium cut-off ) generated by a non-Maxwellian or a non-gyrotropic part of the ion distribution functions in the upstream magnetosheath. On 2 September 1981 the properties of the fluctuations observed in the middle of the magnetosheath can be explained by pure AIC waves generated by protons which have reached a bi-Maxwellian equilibrium. For a given wave mode, the phase difference between BVert and the density is sensitive to the shape of the ion and electron distribution functions: it can be a diagnosis tool for natural and simulated plasmas.

Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth's magnetosheath, the ISEE 1-2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5 – 4 × 10–9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to1RE) just downstream of the shock ramp, and close to the magnetopause.

The ISEE-1 and 2 spacecraft contain two complementary experiments to measure the ambient electron density by radio techniques: a propagation experiment which measures the integrated electron density between ISEE-1 and 2, and a resonance sounder which measures the electron density in the vicinity of ISEE-1, and also provides AC electric field data. These experiments have been described elsewhere (Harvey et al., 1978). Results from these two experiments are presented here for the first time. The propagation experiment permits high time resolution studies of density fluctuations in the solar wind and magnetospheric frontier regions. The sounder experiment has detected for the first time plasma resonances in the solar wind and in the Earth’s magnetosheath, as well as in the regions of the magnetosphere where resonances have already been observed by the spacecraft GEOS-1. We present here a preliminary review of the different types of electric field noise observed in the solar wind and magnetosheath, and discuss their relationship to the measured plasma density.

We report results from the first low-frequency radio receiver to be transported into the Jupiter magnetosphere. We obtained dramatic new information, both because Voyager was near or in Jupiter's radio emission sources and also because it was outside the relatively dense solar wind plasma of the inner solar system. Extensive radio spectral arcs, from above 30 to about 1 megahertz, occurred in patterns correlated with planetary longitude. A newly discovered kilometric wavelength radio source may relate to the plasma torus near Io's orbit. In situ wave resonances near closest approach define an electron density profile along the Voyager trajectory and form the basis for a map of the torus. Detailed studies are in progress and are out-lined briefly.

This paper is related to the propagation characteristics of a chorus emission recorded simultaneously by the 4 satellites of the CLUSTER mission on 29 October 2001 between 01:00 and 05:00 UT. During this day, the spacecraft (SC) 1, 2, and 4 are relatively close to each other but SC3 has been delayed by half an hour. We use the data recorded aboard CLUSTER by the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the wave normal directions relative to the Earth’s magnetic field. This calculation is done for the 4 satellites at different times and different frequencies and allows us to check the directions of these waves. Measurements around the magnetic equator show that the parallel component of the Poynting vector changes its sign when the satellites cross the equator region. It indicates that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it is also observed on SC1, SC2, and SC4 that lower intensity waves propagate toward the equator simultaneously with the SC3 intense chorus waves propagating away from the equator. Both waves are at the same frequency. Using the wave normal directions of these waves, a ray tracing study shows that the waves observed by SC1, SC2, and SC4 cross the equatorial plane at the same location as the waves observed by SC3. SC3 which is 30 minutes late observes the waves that originate first from the equator; meanwhile, SC1, SC2, and SC4 observe the same waves that have suffered a Lower Hybrid Resonance (LHR) reflection at low altitudes (based on the ray tracing analysis) and now return to the equator at a different location with a lower intensity. Similar phenomenon is observed when all SC are on the other side of the equator. The intensity ratio between magnetic waves coming directly from the equator and waves returning to the equator is between 0.005 and 0.01, which is in agreement with previously published theoretical calculation of the growth rates with the particle distribution seen by GEOS.Key words. Magnetospheric physics (plasma waves and instabilities) – Ionosphere (wave propagation) – Radio science (magnetospheric physics)

MANY experiments to measure the radio noise intensity in the topside ionosphere have found an intense “band” of noise in the range of frequency between the plasma frequency and the upper hybrid resonance frequency1–4. Various explanations have been suggested, including plasma instability, radiation by energetic particles5 and anomalous behaviour of the antenna impedance4. Data received by the UK-2 (Ariel 2) satellite suggest that the energy for this noise comes from the particles trapped in the inner Van Allen radiation belt.

Data collected by the ISEE dual-spacecraft mission (on November 7, 1977) on a slowly moving, supercritical, high-beta, quasi-perpendicular bow shock are presented, and the local geometry, spatial scales, and stationarity of this shock wave are assessed in a self-consistent Rankine-Hugoniot-constrained frame of reference. Included are spatial profiles of the ac and dc magnetic and electric fields, electron and proton fluid velocities, current densities, electron and proton number densities, temperatures, pressures, and partial densities of the reflected protons. The observed layer profile is shown to be nearly phase standing and one-dimensional in a Rankine-Hugoniot frame, empirically determined by the magnetofluid parameters outside the layer proper.

An attempt is made to explain the observed frequency-time profiles of type III solar radiobursts in terms of a rapid plasma wave decay rate combined with the exciter model recently proposed by the author. The decay rate is assumed to be sufficiently rapid for the plasma wave energy density profile to be similar to the excitor power density time profile; this is consistent with the exciter model, the rapid decay being caused by Landau damping on the electrons of the modified high energy tail of the ambient plasma electron velocity distribution. The model is compared with radio observations by making simple assumptions about the dependence of the radio intensity upon the plasma wave energy. A comparison is made with simultaneous radio and electron observations by further assuming a simple power-law velocity distribution for the electrons at their point of ejection from the Sun.

The analysis of the fluid continuum level within the shock layer observed on November 7, 1977 by the ISEE satellites (Scudder et al., 1986) is extended to examine, within the framework of Vlasov electrodynamics, direct observational evidence for 'collisionless' resistivity. The analysis is based on the measured wave turbulence and the deviation of the observed electron velocity distribution function from the form predicted using the reversible individual electron trajectories in the presence of dc forces.

Plasma waves associated with the magnetosphere from the magnetosheath to the outer magnetosphere are investigated to obtain a clear definition of the boundaries and regions, to characterize the waves observed in these regions, to determine which wave modes are present, and to determine their origin. Emphasis is on high time resolution data and a comparison between measurements by different antenna systems. It is shown that the magnetosheath flux transfer events, the magnetopause current layer, the outer magnetosphere, and the boundary layer can be identified by their magnetic field and plasma wave characteristics, as well as by their plasma and energetic particle signatures. The plasma wave characteristics in the current layer and in the boundary layer are very similar to the features in the flux transfer events, and upon entry into their outer magnetosphere, the plasma wave spectra are dominated by intense electromagnetic chorus bursts and electrostatic emissions.