Signatures of field‐aligned currents in Saturn's nightside magnetosphere

Talboys, D. L.; Arridge, C. S.; Bunce, E. J.; Coates, A. J.; Cowley, S. W. H.; Dougherty, M. K.; Khurana, K. K.

doi:10.1029/2009gl039867

Cited by 39 publications

(76 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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.…”

Section: Introductionmentioning

confidence: 60%

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

et al. 2015

Self Cite

View full text Add to dashboard Cite

We investigate the magnetic perturbations associated with field‐aligned currents observed on 34 Cassini passes over the premidnight northern auroral region during 2008. These are found to be significantly modulated not only by the northern planetary‐period oscillation (PPO) system, similar to the southern currents by the southern PPO system found previously, but also by the southern PPO system as well, thus providing the first clear evidence of PPO‐related interhemispheric current flow. The principal field‐aligned currents of the two PPO systems are found to be co‐located in northern ionospheric colatitude, together with the currents of the PPO‐independent (subcorotation) system, located between the vicinity of the open‐closed field boundary and field lines mapping to ~9 Saturn radius (Rs) in the equatorial plane. All three systems are of comparable magnitude, ~3 MA in each PPO half‐cycle. Smaller PPO‐related field‐aligned currents of opposite polarity also flow in the interior region, mapping between ~6 and ~9 Rs in the equatorial plane, carrying a current of ~ ±2 MA per half‐cycle, which significantly reduce the oscillation amplitudes in the interior region. Within this interior region the amplitudes of the northern and southern oscillations are found to fall continuously with distance along the field lines from the corresponding hemisphere, thus showing the presence of cross‐field currents, with the southern oscillations being dominant in the south, and modestly lower in amplitude than the northern oscillations in the north. As in previous studies, no oscillations related to the opposite hemisphere are found on open field lines in either hemisphere.

show abstract

Section: Introductionmentioning

confidence: 60%

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

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…Talboys et al . [, ] showed that the azimuthal field data have a number of features in common with those observed in 2006–2007 near noon and dusk, and a number of differences. Specifically, lagging fields were present on open field lines in both hemispheres, increasing in strength on outer closed field lines in association with an outer downward current ~1–2 MA rad −1 , then dropping to smaller and in some cases reversed leading field values in association with an upward current of similar magnitude to those observed prenoon, ~2–5 MA rad −1 .…”

Section: Introductionmentioning

confidence: 83%

“…Lagging fields associated with plasma subcorotation, for example, produce negative azimuthal fields in the northern hemisphere and positive azimuthal fields in the southern hemisphere relative to the northern spin axis (see Figure introduced in section 1.1). Such perturbations have been observed on sequences of inclined Cassini orbits that reach to high polar latitudes, where not only lagging fields were observed indicative of subcorotation, however, but also variable layers of “leading” fields of opposite polarity, indicative of supercorotation [ Bunce et al ., ; Talboys et al ., , , ]. Southwood and Kivelson [] and Talboys et al .…”

Section: Introductionmentioning

confidence: 99%

“…Such a study is undertaken in the present paper, using the same extended sequence of Cassini high‐latitude passes over Saturn's nightside auroral regions during 2008 as investigated by Talboys et al . [, ], but focusing specifically on the southern hemisphere for reasons to be discussed below. In the following subsections we review the above topics in greater detail, focusing in particular on the expected nature of the subcorotation and PPO current systems in order to both guide the analysis and inform the interpretation of results.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Field‐aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components

et al. 2014

Self Cite

View full text Add to dashboard Cite

We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern postmidnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are separated from PPO-related currents using the antisymmetry of the latter with respect to PPO phase. PPO-independent downward currents~1.1 MA per radian of azimuth flow over the polar open field region indicative of significant plasma subcorotation are enhanced in an outer plasma sheet layer of elevated ionospheric conductivity carrying~0.8 MA rad À1and close principally in an upward directed current sheet at~17°-19°ionospheric colatitude carrying 2.3 MA rad À1 that maps to the outer hot plasma region in Saturn's magnetosphere (equatorial rangẽ 11-16 Saturn radii (R S )) colocated with the UV oval. Subsidiary downward and upward currents~0.5 MA rad À1 lie at~19°-20.5°colatitude mapping to the inner hot plasma region, but no comparable currents are detected at larger colatitudes mapping to the cool plasma regime inside~8 R S . PPO-related currents at~17.5°-20°colatitude overlap the main upward and subsidiary downward currents and carry comparable rotating upward and downward currents peaking at~1.7 MA rad À1 . The overall current layer colatitude is also modulated with 1°amplitude in the PPO cycle, maximum equatorward adjacent to the peak upward PPO current and maximum poleward adjacent to peak downward PPO current. This phasing requires the current system to be driven from the planetary atmosphere rather than directly from the magnetosphere.

show abstract

“…From the magnetometer data presented in Figure 1g, two upward current regions can be identified (highlighted in red): a first upward current layer on closed field lines typical of the predusk high‐latitude magnetosphere [ Talboys et al , 2009b; Bunce et al , 2010] in the 0620–0640 UT time interval, and a second (unusual) upward current layer coincident with the SKR source region, in the 0750–0900 UT time interval. In both cases there are no obvious strong asymmetries in the electron flux to indicate larger downgoing fluxes in order to carry the field‐aligned currents suggested by the magnetometer data.…”

Section: Observations In the Upward Current Regions And Skr Source Rementioning

confidence: 99%

Auroral electron distributions within and close to the Saturn kilometric radiation source region

et al. 2011

Self Cite

View full text Add to dashboard Cite

[1] On 17 October 2008, Cassini observed for the first time the electron populations associated with the crossing of a Saturn kilometric radiation source region and its surroundings. These observations allow for the first time the constraint and quantification of the high-latitude acceleration processes, the current systems, and the origin of the low-frequency electromagnetic waves. Enhanced fluxes of field-aligned energetic electrons were measured by the Cassini electron plasma spectrometer in conjunction with unusual intense field-aligned current systems identified using the magnetometer instrument. In the region where downward field-aligned currents were measured, electron data show evidence of two types of upward accelerated electron beams: a broadband energetic (1-100 keV) electron population that is observed throughout the region and a narrow-banded (0.1-1 keV) electron population that is observed sporadically. In the regions where the magnetic field signatures showed evidence for upward field-aligned currents, we observe electron loss cone distributions and some evidence of shell-like distributions. Such nonthermal electron populations are commonly known as a potential free energy source to drive plasma instabilities. In the downward current region, the low-energy and energetic beams are likely the source of the very low frequency emissions. In the upward current region, the shell distribution is identified as a potential source for Saturn kilometric radiation generation via the cyclotron maser instability.

show abstract

Signatures of field‐aligned currents in Saturn's nightside magnetosphere

Cited by 39 publications

References 12 publications

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

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

Field‐aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components

Auroral electron distributions within and close to the Saturn kilometric radiation source region

Contact Info

Product

Resources

About