On the links between the radio flux and magnetodisk distortions at Jupiter

摘要

Using measurements of the Galileo magnetometer and plasma wave instrument, it is shown that the flux of the Jovian auroral radio emissions is correlated with the azimuthal component of the magnetic field (B_φ) measured in the plasma disk, the situations of large magnetic twist of the disk (large ΔB_φ, the difference between the measured and the model field) corresponding to enhanced radio intensities (frequency>300 kHz). For the four orbits discussed here (three in the postmidnight and one in the premidnight sector), representing ~44 days of observations, from 25 to 85 Jovian radius in the magnetodisk, the radio intensity observed during periods of small radial current (ΔB_φ5–6 nT). It is proposed that these variations are the direct consequences of enhanced magnetosphere/ionosphere coupling current systems linked to episodes of larger outward mass outflows in the disk, resulting in larger parallel currents and, thus, in enhanced auroral activity. The application of Hill's model shows that the observed variations of B_φ can be explained by increasing the mass outflow rate from ~150 kg/s (quiet periods) to more than 2 t/s ("energetic" events), for Pedersen conductance ranging from 0.1 to 1 S. This is consistent with the canonical values given in the literature. It is estimated that these modulations of the mass flow rates lead to variations of the power dissipated in the disk from ~10~(14) to 10~(15)W due to the torque exerted by the magnetic coupling with Jupiter's ionosphere, with a conversion rate into the power radiated by the radio waves of the order of 10~(-6).