|
|
 |
|
|
Ann. Geophys., 19, 1711-1720, 2001
www.ann-geophys.net/19/1711/2001/
© European Geosciences Union 2001
How to determine the thermal electron density and the magnetic field strength from the Cluster/Whisper observations around the Earth
J. G. Trotignon1, P. M. E. Décréau1, J. L. Rauch1, O. Randriamboarison1, V. Krasnoselskikh1, P. Canu2, H. Alleyne3, K. Yearby3, E. Le Guirriec1, H. C. Séran1, F. X. Sené1, Ph. Martin1, M. Lévêque1, and P. Fergeau1
1Laboratoire de Physique et Chimie de l’Environnement, Centre National de la Recherche Scientifique, 3 A avenue de la Recherche Scientifique, F-45071 Orléans cedex 02, France
2Centre d’Etudes des Environnements Terrestres et Planétaires, Centre National de la Recherche Scientifique, Université Versailles Saint-Quentin-en-Yvelines, 10 avenue de l’Europe, F-78140, Vélizy Villacoublay, France
3Space Instrumentation Group, Department of ACSE, University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK
Abstract. The Wave Experiment
Consortium, WEC, is a highly integrated package of five instruments used to
study the plasma environment around the Earth. One of these instruments, the
Waves of HIgh frequency and Sounder for Probing of Electron density by
Relaxation, Whisper, aims at the thermal electron density evaluation and
natural wave monitoring in the 4–83 kHz frequency range. In its active
working mode, which is our primarily concern here, the Whisper instrument
transmits a short wave train at a swept frequency and receives echoes after a
delay. Incidentally, it behaves like a classical ground-based ionosonde.
Natural modes of oscillations may thus be excited in the surrounding medium.
This means that with suitable interpretations, the Whisper sounding technique
becomes a powerful tool for plasma diagnosis. By taking into account the
characteristic frequencies of the magnetoplasmas encountered by the Cluster
spacecraft, it is indeed possible to reliably and accurately determine the
electron density and, to a lesser degree, the magnetic field strength from the
Whisper electric field measurements. Due to the predominantly electrostatic
nature of the waves that are excited, observations of resonances may also lead
to information on the electron velocity distribution functions. The existence
of a hot population may indeed be revealed and the hot to cold density ratio
can be estimated.
Key words. Magnetospheric physics
(plasma waves and instabilities). Space plasma physics (active perturbation
experiments; instruments and techniques)
Full Article in PDF (942 KB) |
|
|
