Field‐Aligned Currents in Saturn's Magnetosphere: Observations From the F‐Ring Orbits. Issue 5 (22nd May 2018)

• Record Type: Journal Article
• Authors: Hunt, G. J.; Provan, G.; Bunce, E. J.; Cowley, S. W. H.; Dougherty, M. K.; Southwood, D. J.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 3806
• Page End: 3821
• Publication Date: 2018-05-22
• Subjects: Saturn -- field‐aligned currents -- magnetosphere -- periodicities -- F‐ring orbits -- Cassini; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2017JA025067
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We investigate the azimuthal magnetic field signatures associated with high‐latitude field‐aligned currents observed during Cassini's F‐ring orbits (October 2016–April 2017). The overall ionospheric meridional current profiles in the northern and southern hemispheres, that is, the regions poleward and equatorward of the field‐aligned currents, differ most from the 2008 observations. We discuss these differences in terms of the seasonal change between data sets and local time (LT) differences, as the 2008 data cover the nightside while the F‐ring data cover the post‐dawn and dusk sectors in the northern and southern hemispheres, respectively. The F‐ring field‐aligned currents typically have a similar four current sheet structure to those in 2008. We investigate the properties of the current sheets and show that the field‐aligned currents in a hemisphere are modulated by that hemisphere's "planetary period oscillation" (PPO) systems. We separate the PPO‐independent and PPO‐related currents in both hemispheres using their opposite symmetry. The average PPO‐independent currents peak at ~1.5 MA/rad just equatorward of the open closed field line boundary, similar to the 2008 observations. However, the PPO‐related currents in both hemispheres are reduced by ~50% to ~0.4 MA/rad. This may be evidence of reduced PPO amplitudes, similar to the previously observed weaker equatorial oscillations at similar dayside LTs. We do not detect the PPO current systems' interhemispheric component, likely a result of the weaker PPO‐related currents and their closure within the magnetosphere. We also do not detect previously proposed lower latitude discrete field‐aligned currents that act to "turn off" the PPOs. Key Points: We examine the northern and southern field‐aligned currents (FAC) from the Cassini F‐ring orbits and compare to previous 2008 observations FACs are modulated as expected by the planetary period oscillations (PPOs) but are generally weaker compared to 2008 observations Differences found in the meridional current profiles in the polar and equatorial regions are thought to be related to season and local time