Jean Gabriel Trotignon

Plasma wave system measurements of the Martian bow shock from the Phobos 2 spacecraft

The high-resolution data of the electric field observations performed by the plasma wave system (PWS) during some of the Martian bow shock intersections by Phobos 2 were analyzed. Plasma and wave detectors are very useful instruments for locating the shock transition region and studying structures in the upstream region, such as the foot or the electron foreshock. The electron plasma oscillations that develop in the latter give access to the plasma density of the solar wind. Shock surface models derived from the PWS data are compared to those obtained by other authors, and attention is paid to similarities and differences between the electric field measurements obtained for Mars, Venus, and Earth

Location of the Martian bow shock measurements by the plasma wave system on Phobos 2

During the early months of 1989, the Plasma Wave System, PWS, onboard the Soviet spacecraft Phobos-2 made plasma and electric-field spectrum measurements near the Martian bow shock. A total of 26 shock boundaries were unambiguously identified in the PWS data coming from the high-resolution mode. The location of these boundaries was modeled and the results compared with other studies. Despite the limited coverage of the Phobos-2 observations, the previous shock-surface models and ours show a relatively good agreement.

Testing of the backward wave oscillator model by using the spectral characteristics of VLF chorus elements

A generation mechanism for chorus was suggested by Trakhtengerts (1995) on the basis of the backward wave oscillator (BWO) regime of the magnetospheric cyclotron maser. According to this model, step-like deformation on the electron distribution function is the most important factor of chorus generation, but such a feature is very difficult to observe. By measuring the frequency sweep rates in chorus elements detected by the Cluster spacecraft we determine the mean values and distributions of a dimensionless parameter characterizing the step feature. These values are in agreement with the results of numerical simulations of chorus elements based on the BWO model.

Lessons learned from WHISPER relaxation sounder in ten years of CLUSTER mission

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 Fp, electron plasma frequency, and of Fce, electron gyro-frequency. Those quantities give access to electron density and intensity of magnetic field, key parameters defining local plasma regime. WHISPER sounders 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, Fp and Fce frequency values are far above the working frequency range of the instrument. This range, however, includes the lower hybrid frequency, Flh, which shows up as a clear resonance triggered by the sounder, and allows measurement of Ne whenever Fp/Fce < 1.