The response of Saturn’s dawn field-aligned currents to magnetospheric conditions during the Proximal Orbits

Abstract:

The Proximal Orbits of the Cassini spacecraft during 2017 have given us the opportunity to examine the auroral field-aligned currents in the northern hemisphere dawn sector in relation to wider magnetospheric conditions. Here we will combine the results of three recent studies on the properties of the auroral field-aligned current, magnetospheric ring current and the overall compressional state of Saturn’s magnetosphere due to solar wind conditions. Using these results, we will examine the response of the auroral field-aligned currents in combination with the magnetospheric ring current to compressions and expansions of the Saturnian magnetosphere. We will show that for a compression of Saturn’s magnetosphere the current within in the downward current sheet, directed into the ionosphere, and located equatorward of the main auroral oval increases in strength with increasing total ring current. While the inverse relation occurs during an interval of quiet or expanded magnetospheric conditions. This response is akin to an Earth-like ‘region 2’ field aligned current within Saturn’s dawn magnetosphere. We will discuss the position of this current in relation to the hot plasma population within the magnetosphere. We will also discuss the implications of these observations for Saturn’s magnetospheric current systems and dynamics.