Survey of Saturn <i>Z</i>‐mode emission

Menietti, J. D.; Averkamp, T. F.; Ye, Shengyi; Horne, Richard B.; Woodfield, E. E.; Shprits, Y. Y.; Gurnett, D. A.; Persoon, A. M.; Wahlund, Jan‐Erik

doi:10.1002/2015ja021426

Cited by 13 publications

(56 citation statements)

References 30 publications

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“…We suggest the localized nature of this acceleration could explain the observed asymmetries in the high-energy electron population in this region 24 as asymmetries in Z-mode wave intensity are also observed 14 . Our results suggest that Z-mode waves may also play an important role in radiation belt dynamics at Jupiter, particularly inside the orbit of Io where the plasma density is low, and also at the other magnetized planets of the solar system.…”

Section: Discussionmentioning

confidence: 64%

“…Figure 5a, b show how the strength of the acceleration by Z-mode waves varies with radial distance. The changes in plasma density and magnetic field strength parameters counteract the increase in wave strength as we move closer to the planet 14 by shifting upwards the energy range over which electrons resonate with the Z-mode waves. Inside ~2.7 R S the acceleration becomes slower, although it is still present all the way to the outer edge of the A-ring at 2.3 R s .…”

Section: Resultsmentioning

confidence: 97%

“…The plasma density drops off very rapidly with latitude and also decreases notably away from the plasma source of Enceladus. Z-mode waves are frequently observed inside 4 R S where the combination of low plasma density and higher magnetic field strength resulting from proximity to the planet allows an abundance of Z-mode waves to propagate 14 . A case study of Z-mode waves at Saturn 16 assumed that the direction of wave propagation with respect to the magnetic field (known as the wave normal angle (WNA)) was highly oblique.…”

Section: Resultsmentioning

confidence: 99%

“…The intensity of the Z-mode waves varies with radial distance from Saturn, exponentially increasing towards the planet 14 . Figure 5a, b show how the strength of the acceleration by Z-mode waves varies with radial distance.…”

Section: Resultsmentioning

confidence: 99%

“…However, at Saturn a combination of lower chorus wave power and higher plasma density means that electron acceleration by chorus waves is very weak 11 . We suggest that a different approach is required at Saturn where magnetic and plasma conditions are such that Z-mode waves are intense inside 4 R S 14 . Initial studies of Z-mode interactions with electrons at the Earth show they are a very good candidate for electron acceleration 7,15 .…”

Section: Introductionmentioning

confidence: 99%

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Formation of electron radiation belts at Saturn by Z-mode wave acceleration

et al. 2018

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At Saturn electrons are trapped in the planet’s magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.

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Section: Discussionmentioning

confidence: 64%

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formation of electron radiation belts at Saturn by Z-mode wave acceleration

et al. 2018

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Source region and growth analysis of narrowband Z‐mode emission at Saturn

et al. 2016

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Intense Z‐mode emission is observed in the lower density region near the inner edge of the Enceladus torus at Saturn, where these waves may resonate with MeV electrons. The source mechanism of this emission, which is narrow‐banded and most intense near 5 kHz, is not well understood. We survey the Cassini Radio and Plasma Wave Science data to isolate several probable source regions near the inner edge of the Enceladus density torus. Electron phase space distributions are obtained from the Cassini Electron Spectrometer, part of the Cassini Plasma Spectrometer investigation. We perform a plasma wave growth analysis to conclude that an electron temperature anisotropy and possibly a weak loss cone can drive the Z mode as observed. Electrostatic electron acoustic waves and perhaps weak beam modes are also found to be unstable coincident with the Z mode. Quasi‐steady conditions near the Enceladus density torus may result in the observations of narrowband Z‐mode emission at Saturn.

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Survey of Saturn electrostatic cyclotron harmonic wave intensity

et al. 2017

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We conduct a survey of electrostatic electron cyclotron harmonic (ECH) emissions observed at Saturn by the radio and plasma wave science investigation on board the Cassini spacecraft. These emissions are known to be effective at interacting with electrons in the terrestrial inner magnetosphere, producing electron scattering into the loss cone and acceleration (cf. Horne and Thorne, 2000; Thorne et al., 2010). At Saturn ECH emission occurs with high probability and at strong intensity near the magnetic equator, outside the Enceladus torus in the range ~5 < L < ~10. Inside the inner boundary of the torus, ECH emissions are also observed near the equator and at higher latitude. Intensity levels of ECH emission are comparable to those observed at Earth, higher than Saturn chorus and Z‐mode emission, and are likely to scatter electrons into the loss cone as at Earth. ECH waves are particularly intense and extend to higher harmonics within some plasma injection regions. We present results for a survey of over 8 years of Saturn data for fundamental and up to three harmonics of fce, the electron cyclotron frequency.

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Survey of Saturn Z‐mode emission

Cited by 13 publications

References 30 publications

Formation of electron radiation belts at Saturn by Z-mode wave acceleration

Formation of electron radiation belts at Saturn by Z-mode wave acceleration

Source region and growth analysis of narrowband Z‐mode emission at Saturn

Survey of Saturn electrostatic cyclotron harmonic wave intensity

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