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

Roussos, E.; Krupp, N.; Mitchell, D. G.; Paranicas, C.; Krimigis, S. M.; Andriopoulou, M.; Palmaerts, Benjamin; Kurth, W. S.; Masters, A.; Dougherty, M. K.

doi:10.1016/j.icarus.2015.04.017

Cited by 41 publications

(85 citation statements)

References 57 publications

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“…This picture would be consistent with the observations of Mitchell et al (2016), Roussos et al (2016), Palmaerts et al (2016), and Bader et al (2019), who discuss observations of~1-hr periodicities of LEMMS and RPWS data. These observations are consistent with SKR occurring along a recently reconnected field line containing an upward current (downward electrons) while the auroral hiss occurs along return current (upward electrons).…”

Section: Discussionsupporting

confidence: 91%

“…These observations have a parallel with terrestrial electron beam-generated auroral hiss seen on downward current field lines near upward current magnetic field lines supporting auroral kilometric radiation source regions (Gurnett et al, 1983). In addition, Roussos et al (2016) and Palmaerts et al (2016) demonstrate that the~1-hr periodicities of Cassini LEMMS injection signatures lie mainly outside of Titan's orbit (20 Rs), often close to the magnetopause, and predominantly on the duskside; however, Palmaerts et al (2016) identified~1-hr electron pulsations in the high-latitude magnetosphere as well, some of them simultaneous with auroral hiss quasiperiodic oscillations. These authors suggest that they are related to electron injections and auroral hiss observations, and are likely due to "recurrent small-scale magnetodisk reconnection on closed field lines."…”

Section: Introductionmentioning

confidence: 52%

“…occur at lower latitude than the periodic auroral hiss episodes in each hemisphere Roussos et al (2016). We plot (top) low-rate hiss intensity, (middle) LEMMS detrended electron flux, and (bottom) electron pitch angle data.…”

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confidence: 99%

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Quasiperiodic Saturn Auroral Hiss Observed During a Cassini Proximal Orbit

Menietti

Palmaerts²,

Zãhlava

et al. 2020

JGR Space Physics

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Saturn auroral hiss is intense whistler mode emission similar in morphology to terrestrial auroral hiss, and is observed at high latitude very often in quasiperiodic episodes with a period of approximately 1 hr. Bader et al. (2019) report auroral pulsations that may be due to duskside magnetodisk reconnection. The source of the 1-hr period is not definitively known but has been purported to be due to second harmonic Alfven waves standing along near planet magnetic field lines (Yates et al., 2016). Observations of auroral hiss at high latitude along Cassini proximal orbits are often excellent, and we have focused on an event for which we have concurrent ultraviolet auroral images as well as electron flux data. A series of repeating auroral hiss episodes is observed to initiate near the magnetic field line that traverses a Saturn kilometric radiation source region in each hemisphere, with periodic episodes of hiss recurring at higher L-shells. Magnetic field lines centered on individual hiss episodes have auroral footprints that lie near and within a region of intense auroral ultraviolet emissions. These observations have a parallel in terrestrial return current electron beam-generated auroral hiss seen near magnetic field lines supporting auroral kilometric radiation source regions. Recent findings link periodic plasma injections with Saturn reconnection sites observed preferentially on the duskside. These injections may spawn Saturn kilometric radiation source regions and periodic auroral hiss emission in nearby return current regions.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 52%

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Quasiperiodic Saturn Auroral Hiss Observed During a Cassini Proximal Orbit

Menietti

Palmaerts²,

Zãhlava

et al. 2020

JGR Space Physics

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“…Two surveys have been conducted of short periodicities, and both involve energetic electrons measured by Cassini instruments. The first of these investigated quasi‐periodic injections of relativistic electrons [ Roussos et al ., ]. These injections had recurrence periods of ~60 min and were generally observed outside Titan's orbit (at 20 R S , 1 R S = 60,268 km = Saturn radius) over a wide range of latitude and local time.…”

Section: Introductionmentioning

confidence: 95%

Short periodicities in low‐frequency plasma waves at Saturn

2016

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Short‐period amplitude modulations (~60 min period) have been detected in the ~100 Hz plasma wave emissions observed by the Radio Plasma Wave Science instrument on the Cassini spacecraft in orbit around Saturn. These periodicities were detected throughout the mission from mid‐2004 to the present, and this is the first statistical study of them. The modulations are observed throughout the magnetosphere and can last from ~2 h to ~20 h, although the duration may be biased by spacecraft observing conditions. The periodicities are statistically much more likely to be seen at high latitudes, both north and south, and at local times between dusk and midnight. When corrected for latitude and local time, the occurrence frequency has declined in time since 2005. Considering all observations, the mean period of these events is 65.3 ± 20.7 min, with a peak (modal value) at 63.3 min. The period has no dependence on local time or latitude. Alfvén waves have interhemispheric transit times commensurate with the mean periods and should thus be considered principal candidates for their production.

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“…Clark et al (2014) extended this work by providing a complete summary of energetic electron PADs from 2004 to 2012. Within quasiperiodic events (called "QP60 events" wherein fluxes have periods of~60 min), the PADs are likely to have strongly bidirectional distributions and may be associated with certain plasma wave and magnetic field fluctuations (Palmaerts et al, 2016;Roussos et al, 2016). A plasmasphere-like boundary, detected at high latitudes using Langmuir probe and plasma wave data, was associated with a change in the PADs of energetic electrons, signaling open magnetic field lines on the poleward side of this boundary .…”

Section: Introductionmentioning

confidence: 99%

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

Carbary

Mitchell

Kollmann

et al. 2018

Geophysical Research Letters

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Pitch angle distributions (PADs) of very energetic electrons (110–365 keV) are examined during the ring‐grazing and proximal orbits of the Cassini spacecraft, from day 320 2016 (15 November) to day 257 2017 (14 September). These repeating orbits allowed a statistical evaluation of the PADs within the magnetopause on the nightside of Saturn. Along L‐shells (i.e., equatorial crossing distances of magnetic field lines) near and outside that of Titan and north of the equator, the electron fluxes were unidirectionally field‐aligned going away from Saturn. Along L‐shells inside Titan's and south of the equator, the electrons had bidirectional or pancake (trapping) PADs. This behavior suggests that the field lines within Titan's L‐shell are generally closed, while those outside of that L‐shell are generally open. This result strictly applies only to the nightside local times sampled during the final Cassini orbits, but one may infer a similar behavior at other times.

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

Cited by 41 publications

References 57 publications

Quasiperiodic Saturn Auroral Hiss Observed During a Cassini Proximal Orbit

Quasiperiodic Saturn Auroral Hiss Observed During a Cassini Proximal Orbit

Short periodicities in low‐frequency plasma waves at Saturn

Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits

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