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Wave and plasma measurements carried out by the Phobos-2 spacecraft in the Martian environment indicate that a part of solar wind electrons and ions are reflected and accelerated at the Martian bow shock. These particles streaming back into the solar wind lead to the formation of the foreshock region upstream the planetary bow shock. It is shown that the general structure of the foreshock at Mars is similar to that of the foreshock region upstream the Earth’s bow shock. However, the electric emissions observed at frequencies around 100 Hz at the leading edge of electron foreshock at Mars have been never reported for observations in the similar region at Earth. The burst of these waves occurs before the spacecraft enters the electron foreshock identified with the onset of electron plasma waves and calculations of the magnetic connection to the planetary bow shock.

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and search-coil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.

Impedance probes, which are well known in geophysical prospection, in particular for ground permittivity investigations, have been successfully transposed to space plasmas. Transmitting and receiving electrodes are used for measuring on open circuit the dynamic impedance of the system at several fixed frequencies over a range that includes characteristic frequencies of the ambient plasma. The measurements are then interpreted using a suitable theory and the values of plasma parameters, such as the electron density, temperature, and possibly the relative velocity of the plasma and the spacecraft, can be deduced. To show how powerful this technique is, results obtained in the Earth's plasmasphere by the mutual impedance probe onboard ROSETTA are presented.

An original method for calculating and representing the excitation coefficients of longitudinal electron waves is applied to the case of a hot, collisionless, homogeneous and isotropie plasma with a bi-Maxwellian velocity distribution function. Using a Van Kampen treatment we introduce a ‘wave density’ distribution which is represented graphically. When hot electrons are added to a plasma of cool electrons the Landau mode is distorted and its damping increases with the hot/cold temperature ratio θ. The Landau mode separates into two modes for θ ≥ θ0 where θ0 increases as the hot/cold density ratio α decreases. We show that no wave seems to be able to propagate at frequencies below the plasma frequency. Using an abrupt cut-off in the hot electron distribution function, we recover the results for a Maxwellian plus water-bag distribution.

Using a Van Kampen treatment, we study the longitudinal electron oscillations for a plasma with a cut-off Maxwellian velocity distribution. Having defined and computed excitation coefficients in the real w, k plane, we represent this ‘wave density’ through the greyness of this plane. This representation should be useful as a help to the experimenter. Moreover we show the appearance of a slightly damped pole with a phase velocity slightly smaller than the cut-off velocity Vc if this velocity is in the interval 2 to 4VT and a modification of the Landau mode which propagates for higher and higher frequencies when Vc decreases.

The Phobos-2 spacecraft has been inserted in a Mars orbit to rendezvous with one of the two Martian satellites, Phobos, in early 1989. The Plasma Wave System (PWS) is part of the scientific payload; this instrument will record, for the first time in a Martian environment, the spectra of natural waves with an electric dipole in the frequency range 0-150 kHz and measure the ionospheric plasma density distribution with a Langmuir probe. In-flight data show that the system performs well and that PWS should meet its scientific goals.

We study the nonlinear steady state structures created in a one-dimensional collisionless electron plasma by a transparent grid raised to a given potential. Moreover, natural structures, i.e., in the absence of a grid and consequently of any external charge, can also be obtained. For the electrons (here ions are supposed motionless and uniform), the structure must involve a hole in the trapped electron density distribution and is consequently attractive. A relationship between the depth of the potential and its possible length is obtained. These studies are preliminary to the problems of stability and waves propagating in strongly inhomogeneous plasma structures.

Examples of results from a dual satellite (GEOS-1 and ISEE-1) study of terrestrial non-thermal electromagnetic continuum radiation are presented. The problems of sources and generation mechanisms are discussed in the context of simultaneous measurements of radiation arrival directions, radiation cut-offs, and detailed spectral observations. The results, which imply significant contributions from the magnetospheric volume to the low frequency (‘trapped’) component, confirm the near-plasmapause as the source of the higher frequency (‘escaping’) component. The detection of significant X mode radiation and the implied presence of localized non-directive sources lead us to conclude that current theories of generation are inadequate.

The principal objective of the Sounder experiment aboard ISEE 1 is to study the plasma frequency along the spacecraft trajectory. This represents a considerable amount of data for the duration of the mission (3 years). Thus an automatic method is necessary to recognize the plasma resonances. We present here a resonance recognition methodology based on the Sebestyen's discrimination approach. The preliminary results of this method, obtained from a set of known resonances, show a good efficiency (more than 90% of the known plasma resonances are recognized). This method will be used in the future to identify other resonances in the magnetosphere.

We advance the achievements of Interball-1 and other contemporary missions in exploration of the magnetosheath-cusp interface. Extensive discussion of published results is accompanied by presentation of new data from a case study and a comparison of those data within the broader context of three-year magnetopause (MP) crossings by Interball-1. Multi-spacecraft boundary layer studies reveal that in ∼80% of the cases the interaction of the magnetosheath (MSH) flow with the high latitude MP produces a layer containing strong nonlinear turbulence, called the turbulent boundary layer (TBL). The TBL contains wave trains with flows at approximately the Alfvén speed along field lines and "diamagnetic bubbles" with small magnetic fields inside. A comparison of the multi-point measurements obtained on 29 May 1996 with a global MHD model indicates that three types of populating processes should be operative: large-scale (∼few RE) anti-parallel merging at sites remote from the cusp; medium-scale (few thousandkm) local TBL-merging of fields that are anti-parallel on average; small-scale (few hundredkm) bursty reconnection of fluctuating magnetic fields, representing a continuous mechanism for MSH plasma inflow into the magnetosphere, which could dominate in quasi-steady cases. The lowest frequency (∼1–2mHz) TBL fluctuations are traced throughout the magnetosheath from the post-bow shock region up to the inner magnetopause border. The resonance of these fluctuations with dayside flux tubes might provide an effective correlative link for the entire dayside region of the solar wind interaction with the magnetopause and cusp ionosphere. The TBL disturbances are characterized by kinked, double-sloped wave power spectra and, most probably, three-wave cascading. Both elliptical polarization and nearly Alfvénic phase velocities with characteristic dispersion indicate the kinetic Alfvénic nature of the TBL waves. The three-wave phase coupling could effectively support the self-organization of the TBL plasma by means of coherent resonant-like structures. The estimated characteristic scale of the "resonator" is of the order of the TBL dimension over the cusps. Inverse cascades of kinetic Alfvén waves are proposed for forming the larger scale "organizing" structures, which in turn synchronize all nonlinear cascades within the TBL in a self-consistent manner. This infers a qualitative difference from the traditional approach, wherein the MSH/cusp interaction is regarded as a linear superposition of magnetospheric responses on the solar wind or MSH disturbances. Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers) – Space plasma physics (turbulence; nonlinear phenomena)

International audience; Relaxation sounders have proved to be successful in measuring the electron density in dilute space plasmas. The resonances excited at the characteristic frequencies of the medium depend very much on the local plasma. We present here methods to determine automatically, by a computer, the plasma frequency in the various regions encountered. In the solar wind and in the magnetosheath, only one strong, long‐lasting resonance appears close to the plasma frequency fpe, yielding directly the electron density. We use a pattern recognition method based on Sebestyen';s discrimination approach, and each identified resonance is given with a quality criterion. From one year of data there is no drift of the resonance features, and the method is used with a success rate of 95% as determined by manual means. In the magnetosphere various types of resonances are excited at the characteristic frequencies of the medium (cyclotron harmonic frequencies nfce and maximum frequencies of the Bernstein';s modes fqn). We compare the dispersion relation of electrostatic waves, which contains fce and fpe as parameters, to the observed frequencies of the resonances. First fce is extracted using the harmonicity of the nfce resonances, and then the fqn series is compared to the dispersion relation for various values of fpe. In 93% of 250 cases the error for fpe is less than 10%. In the magnetotail where the resonances are closely spaced in frequency, the frequency resolution of the experiment does not allow us to use this method and we determine fpe by the enhancement of the resonances power.