JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. A2, PAGES 2373-2379, FEBRUARY 1, 1997
Detection of Bernstein wave forbidden bands
in the Jovian
magnetosphere: A new way
to measure the electron density
Michel Moncuquet, Nicole Meyer-Vernet, and Sang Hoang
Département de Recherche Spatiale, Observatoire de Paris,
Meudon, France
R. J. Forsyth
The Blackett Laboratory, Imperial College, London
P. Canu
Centre d'Étude des Environnements Terrestres et Planétaires,
Vélizy, France
We analyze the power spectra measured by the radio
receiver of the Unified Radio and Plasma Wave experiment on
Ulysses during its passage through the Jovian inner magnetosphere
from 
in the outskirts of the Io plasma torus to 
near the plasma
sheet. Below the plasma frequency 
, these spectra are weakly banded between
gyroharmonics. These observations were interpreted by
[Meyer-Vernet, Hoang and Moncuquet, 1993]
as quasi-thermal fluctuations in
Bernstein waves. We show that above
each observed gyroharmonic band falls off very abruptly on its high-frequency
side. We interpret it as the ``forbidden band'' predicted by the Bernstein wave
dispersion equation between the so-called 
frequency and the consecutive
gyroharmonic, that is, a region where no Bernstein wave can propagate. This allows a
determination of the local cold plasma frequency and thus of the core electron
density with a 
uncertainty.
As a consistency check, we show that the thus determined are very close
to the frequencies of the resonances excited
by the relaxation sounder on Ulysses.
P. Canu, CETP, 10-12 avenue de l'Europe, 78140 Vélizy, France. (e-mail: canu@cetp.ipsl.fr). S. Hoang, N. Meyer-Vernet, and M. Moncuquet, DESPA, Observatoire de Paris-Meudon, 5 Place Jules Janssen, 92195 Meudon Cedex, France.(e-mail: hoang@megasx.obspm.fr; meyer@obspm.fr; moncuquet@obspm.fr). R. J. Forsyth, The Blackett Laboratory, Imperial College, London, SW7 2BZ, United Kingdom.(e-mail: r.forsyth@ic.ac.uk)
Received June 13, 1996; revised September 27, 1996; accepted October 24, 1996