Statistical characteristics of field-aligned currents in Saturn's nightside magnetosphere

Abstract

[1] During 2008, the Cassini spacecraft traversed Saturn's high-latitude field-aligned current systems on sequential north-south periapsis passes in the nightside magnetosphere. Two types of current systems have previously been identified, associated with antisymmetric azimuthal field signatures in the northern and southern hemispheres. The first exhibits exclusively "lagging" field morphology, while the second also includes an equatorward interval of "leading" field. Here we report the statistical characteristics of these currents, their strength, ionospheric location, and relationship to plasma boundaries. From high to low latitude, the first type comprises a downward current followed by an upward current, whose strengths are ∼0.5-3.5 MA per radian of azimuth. The downward current maps to ionospheric colatitudes of ∼13.5°and ∼16°in the north and south, respectively, usually centered in the outer magnetosphere, while the upward current maps to ∼16.5°and ∼19°in the north and south, located within the ring current region. The second type comprises a distributed downward current of ∼1-2 MA rad −1 flowing in the open field and outer magnetosphere regions, followed by an upward current of ∼2.5-5 MA rad −1 mapping to ∼15.5°and ∼18°in the north and south, corresponding to the outer magnetosphere and outer ring current, and a further downward current of ∼1-2.5 MA rad −1 mapping to ∼17.5°and ∼20°in the north and south, corresponding to the inner ring current.

Field‐aligned currents in Saturn's northern nightside magnetosphere: Evidence for interhemispheric current flow associated with planetary period oscillations

“…It was found that the form of the currents was well organized by the southern PPO phase and that these PPO-related variations give rise to the differing current morphologies noted previously by Talboys et al [2009Talboys et al [ , 2011 in initial study of this data. No obvious evidence was found for a strong influence at the northern period, the hypothesized interhemispheric currents shown in Figures 1d and 1g not withstanding.…”

Quasi-periodic injections of relativistic electrons in Saturn’s outer magnetosphere

“…11). The main aurora emission is located near or at the boundary between open and closed field lines Talboys et al, 2011). Field line tracing for the QP60 poleward of the main emission also indicates that they reside on open field lines, although this result depends on the set-up of the K06 magnetic field model.…”

Energetic Particle Signatures Above Saturn's Aurorae

“…FACs in Saturn's auroral regions have previously been investigated in detail based on magnetometer data (e.g., Cowley et al, 2008;Hunt et al, 2014Hunt et al, , 2015Hunt et al, , 2016Hunt et al, , 2018Talboys et al, , 2011, but Cassini's orbit greatly limited our ability to characterize the acceleration region in more detail before the last low spacecraft passes across the auroral region. FACs in Saturn's auroral regions have previously been investigated in detail based on magnetometer data (e.g., Cowley et al, 2008;Hunt et al, 2014Hunt et al, , 2015Hunt et al, , 2016Hunt et al, , 2018Talboys et al, , 2011, but Cassini's orbit greatly limited our ability to characterize the acceleration region in more detail before the last low spacecraft passes across the auroral region.…”