The source of Saturn's periodic radio emission

Abstract

This paper proposes a model of the link between the pulsing radio signals from Saturn (Saturn kilometric radiation), known to be most intense on the morningside, and the rotating magnetic (cam) field structure identified on low‐latitude orbits. On the high‐inclination orbits of the Cassini spacecraft in late 2006, large‐scale azimuthal deviations of the magnetic field, corresponding to upward field‐aligned currents, have been detected in the late morning sector. There is evidence that their intensity is modulated by the rotating cam magnetic field, the periodic field structure seen deeper inside the magnetosphere. It is proposed that the local intensification of field‐aligned currents that gives rise to the modulation of the radio signal occurs in conjunction with the passage through the morning magnetosphere of the swept‐forward sector of the perturbation field imposed beyond the shells that carry the cam currents. The morningside magnetosphere is unique as a region in which not only does the magnetopause compress rotating plasma inside the magnetosphere but also magnetic shear develops between the magnetic shells of the middle magnetosphere and an outer region of magnetic field swept back by the solar wind. The link between radio pulsing and magnetic rotation arises through the interaction of the cam currents with structures unique to this part of the magnetosphere.