Measuring the stress state of the Saturnian magnetosphere

The dynamics of a planetary magnetosphere can be quantified by subtracting the system's ground'' state from the observed state and tracking their difference. When a magnetosphere is stressed, by external and internal forces, the magnetic field lines become stretched or compressed. In this paper, we construct an index of the stress state of the Saturnian magnetosphere using magnetometer measurements made in the equatorial inner magnetosphere. This index is analogous to the Dst index produced for Earth's magnetosphere and a stress index created for Jupiter from the Galileo magnetometer data. This index identifies infrequent large perturbations of the magnetosphere from its ground state, and the smaller deviations that are consistent in duration and magnitude with those expected from pressure variations in the solar wind.