Remote sensing of the Io torus plasma ribbon using natural radio occultation of the Jovian radio emissions

摘要

We study the Jovian hectometric (HOM) emissions recorded by the RPWS (Radio and Plasma WaveScience) experiment onboard the Cassini spacecraft during its Jupiter flyby.We analyze the attenuation band associated with the intensityextinction of HOM radiation. This phenomenon is interpreted as arefraction effect of the Jovian hectometric emission inside the Ioplasma torus. This attenuation band was regularly observed during periods ofmore than 5 months, from the beginning of October 2000 to the end ofMarch 2001. We estimate for this period the variation of theelectron density versus the central meridian longitude (CML). Wefind a clear local time dependence. Hence the electron density wasnot higher than 5.0 × 104 cm?3 during 2 months, when thespacecraft approached the planet on the dayside. In the lateafternoon and evening sectors, the electron density increases to1.5 × 105 cm?3 and reach a higher value at some specific occasions.Additionally, we show that ultraviolet and hectometric wavelengthobservations have common features related to the morphology of theIo plasma torus. The maxima of enhancements/attenuations of UV/HOMobservations occur close to the longitudes of the tip of themagnetic dipole in the southern hemisphere (20° CML) and inthe northern hemisphere (200° CML), respectively. This is asignificant indication about the importance of the Jovian magneticfield as a physical parameter in the coupling process betweenJupiter and the Io satellite.