Rapid Electron Acceleration in Low‐Density Regions of Saturn's Radiation Belt by Whistler Mode Chorus Waves

Woodfield, E. E.; Glauert, S. A.; Menietti, J. D.; Averkamp, T. F.; Horne, Richard B.; Shprits, Y. Y.

doi:10.1029/2019gl083071

Cited by 25 publications

(36 citation statements)

References 32 publications

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“…Roussos et al (2018) demonstrated that transport time scales from the middle magnetosphere to Saturn's electron radiation belts due to time-variable electric fields with a fixed local time pattern are on the order of 1-2 weeks. A competing process of wave-driven acceleration requires time scales of ∼ 1 day (Woodfield Glauert et al, 2019) around L = 5 to ∼100 days (Woodfield Horne et al, 2018) much further in. The convection and wave acceleration time scales are comparable at L > 5.…”

Section: Resultsmentioning

confidence: 99%

Spectral Signatures of Adiabatic Electron Acceleration at Saturn Through Corotation Drift Cancelation

Sun

Roussos

Krupp

et al. 2019

Geophysical Research Letters

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The energetic electron spectra of Saturn's radiation belts are studied using Cassini's 13 years of measurements by the Magnetosphere Imaging Instrument/Low Energy Magnetospheric Measurement System detector. We find that between L shells (L) of 10 and 4.5 the differential flux spectrum of 0.3‐ to 1.6‐MeV electrons evolves from a single power law to two power law functions separated at an energy cutoff (Ec). We show that inside L∼8, Ec has an L shell dependence that tracks consistently the energy of corotation drift cancelation (or resonance) ECDR, that is, the energy at which magnetic electron drifts and azimuthal corotation cancel, and is not associated with the absorbing effects of Saturn's moons. Ec also deviates from what conservation of the first adiabatic invariant would dictate. Our results verify that electrons around ECDR can be transported radially very efficiently by variable convective flows, such as those related to the noon‐midnight electric field in Saturn's magnetosphere.

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Section: Resultsmentioning

confidence: 99%

Spectral Signatures of Adiabatic Electron Acceleration at Saturn Through Corotation Drift Cancelation

Sun

Roussos

Krupp

et al. 2019

Geophysical Research Letters

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“…At L < 4 R S in Saturn’s magnetosphere, Woodfield et al. (2019) proposed that the acceleration of electrons to relativistic energies by whistler waves may lead to the butterfly PADs observed at L ∼ 3 R S (Paranicas, Mitchell, Krimigis, et al., 2010). It has also been shown that there are intense Z‐mode waves in this area (Menietti et al., 2015, 2016; Ye et al., 2010).…”

Section: Discussion: Pad Inward Of L = 4 Rs and The Implication On Rementioning

confidence: 99%

Cassini Observation of Relativistic Electron Butterfly Distributions in Saturn’s Inner Radiation Belts: Evidence for Acceleration by Local Processes

Yuan

Roussos

Wei

et al. 2021

Geophysical Research Letters

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The morphology of electron pitch angle distributions (PADs) helps to identify dynamic processes in Saturn's magnetosphere. Previous studies demonstrated convective transport being important for relativistic electron acceleration at L>4 in the inner magnetosphere, whereas closer to Saturn the situation is not as well established. We have investigated the PADs of relativistic electrons throughout radiation belts, using 13-year measurements from Cassini spacecraft. Our results show that at 3.57 MeV. These results suggest that convective transport continues to govern down to L=3.5. For even smaller L-shells, the independence of butterfly PAD from energy suggests that the acceleration by resonant interactions of electrons with waves likely serves as an additional key mechanism regulating the dynamics in the core region of radiation belts.

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“…As discussed by Horne and Thorne (1998) and Glauert and Horne (2005), Z-mode can efficiently scatter electrons similar to whistler-mode chorus. This emission has been studied at Saturn by Ye et al (2010), Gu et al (2013), and Menietti et al (2015), and modeled at Saturn by E. E. Woodfield et al (2018Woodfield et al ( , 2019. Source regions for narrowband Z-mode at Saturn are not well understood, but may be near density gradients along the inner edge of the Enceladus torus and near the ring plane in the inner magnetosphere, as well as near Saturn kilometric radiation source regions (cf.…”

Section: Observations Of Whistler-mode Chorus and Hiss Emissionmentioning

confidence: 99%

Low‐Latitude Whistler‐Mode and Higher‐Latitude Z‐Mode Emission at Jupiter Observed by Juno

et al. 2021

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Whistler‐mode chorus emission is important in the scattering and acceleration of electrons and filling of the radiation belts at Jupiter. In this work whistler mode magnetic intensity levels at Jupiter are comprehensively binned and parameterized. The frequency range of whistler mode under study extends from the proton cyclotron frequency, fcH, to fceq/2, where fceq is the cyclotron frequency mapped to the magnetic equator. Parametric dependence of magnetic plasma wave intensity is obtained versus frequency, latitude, and M‐shell, as determined using a current magnetic field model based on Juno data. The results extend similar analyses of Jupiter whistler‐mode emission obtained by the Galileo spacecraft, particularly on the nightside, and provide better coverage in latitude. Peaks in whistler‐mode emission occur near M ∼ 8–9, similar to previous studies, with average peak intensities approaching 10−2 nT2, as also found by Galileo on the dayside. Auroral hiss and probably Z‐mode are observed at higher latitudes. Jovian chorus emissions near an equatorial source region are more broad‐banded than terrestrial chorus, and are coincident with a broad‐banded electron distribution of free energy and strong electron scattering to large pitch angles. Intense whistler mode within a young plasma injection region is also observed, similar to injections in Saturn's magnetosphere. Future study of wave particle interactions within the chorus source region will be important. Possible Z‐mode emission at significant intensity levels is observed in Jupiter's inner magnetosphere, more intense, but not unlike Z‐mode observed at Saturn.

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Rapid Electron Acceleration in Low‐Density Regions of Saturn's Radiation Belt by Whistler Mode Chorus Waves

Cited by 25 publications

References 32 publications

Spectral Signatures of Adiabatic Electron Acceleration at Saturn Through Corotation Drift Cancelation

Spectral Signatures of Adiabatic Electron Acceleration at Saturn Through Corotation Drift Cancelation

Cassini Observation of Relativistic Electron Butterfly Distributions in Saturn’s Inner Radiation Belts: Evidence for Acceleration by Local Processes

Low‐Latitude Whistler‐Mode and Higher‐Latitude Z‐Mode Emission at Jupiter Observed by Juno

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