Spectral Signatures Recorded By WHISPER Sounder Mode On Board CLUSTER2 Mission Inside Different Magnetosphere Regions: Plasma Frequency Determination
Résumé
The Wave of High frequency and Sounder for Probing of Electron density by Relaxation (WHISPER) performs the measurement of the electron density on the four satellites of the CLUSTER2 mission. The two main purposes of the WHISPER experiment are to record the natural waves and to make a diagnostic of the electron density using the sounding technique, the various working modes and the fourier transforms calculated on board provide a good frequency resolution obtained in the bandwidth 2-80 kHz and a well instrumental adaptability to determine the electron density in various plasma. In this presentation, we focus our attention to the active mode when WHISPER is working as a sounder. Cluster2 orbits cross various plasmas around the earth with a weak or a strong magnetic field (solar wind, magnetosheat, cusp, aurora zones, magnetotail etc). Plasma response is strongly different following region. Spectra exhibit numerous resonances where it is difficult to recognize the plasma frequency .We shall show the characteristics features in each region and we shall describe the methods to identify observed resonances as electron gyro frequency and harmonics, plasma frequency, upper-hybrid frequency and Bernstein modes.