Field-aligned currents in Saturn's nightside magnetosphere: subcorotation and planetary period oscillation components during northern spring - Bradley, TJ; Cowley, SWH; Provan, G; Hunt, GJ; Bunce, EJ; Wharton, SJ; Alexeev, II; Belenkaya, ES; Kalegaev, VV; Dougherty, MK (Journal of Geophysical Research: Space Physics, 2018)