Jovian radio wave propagation through the Io plasma torus
Résumé
We report on the Jovian radio wave propagation
through the Io torus plasma. We select cases of
Jovian hectometric (HOM) emission which are
subject to attenuation effect. The morphology of
such phenomena is characterized by the use of
RPWS experiment observations recorded during
the Cassini Jupiter flyby. This attenuation is
shown to depend on the Jovian magnetic field
where clear modulations appear at two central
meridian longitudes around ~180° and ~50°,
corresponding respectively to the position of the
magnetic field axis in the Northern and Southern
hemispheres. A detailed analysis of the dynamic
spectra leads us to confirm (previous work by
Lecacheux, JGR, 85, 1980) the presence of
refraction effect caused by the Io plasma torus.
The Jovian radio wave presents different spectral
features when it propagates through the Io plasma
torus. We note in particular three main cases: a
total emission extinction, a partial decrease of the
radiation and an enhancement of the intensity
before and after the attenuation of HOM emission.
The origins of such spectral effects depend on: the
source location (in the Northern or Southern
hemisphere), the observer position (e.g. Cassini
spacecraft) with regard to the magnetic equator of
the planet, and the electronic density in the Io
torus. We discuss our results and compare them to
previous studies based on data recorded by
Voyager, Galileo and Cassini spacecraft