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

Sun, Yixin; Roussos, E.; Krupp, N.; Zong, Qiugang; Kollmann, P.; Zhou, X.‐Z.

doi:10.1029/2019gl084113

Cited by 14 publications

(21 citation statements)

References 35 publications

(64 reference statements)

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“…Questions remain as to their major trigger, but from the various possibilities available we can safely exclude ICME shocks, while evidences are in favor of CIRs as their candidate trigger. The transients' regularity and fast radial transport, in conjunction with the findings of Sun et al (), indicate that they likely comprise electrons in corotation‐drift resonance. Future work on the transients' electron spectra and further analysis of single events and different aspects of our survey results would be necessary to bring closure to new questions opened here.…”

Section: Discussionsupporting

confidence: 53%

“…One important aspect we know about electron spectra in the MeV range comes from the study of Sun et al (). They surveyed high‐energy resolution electron measurements of LEMMS down to L =5.…”

Section: Discussionmentioning

confidence: 99%

“…For electrons about 1 MeV, the transport process is especially efficient, since around that energy magnetic drifts cancel out corotation, and the convection electric field can easily bring them inward. Sun et al () provided convincing evidence to support this corotation‐drift resonance (cancelation) scenario by the analysis of electron energy spectra obtained throughout the Cassini mission. Roussos et al () argued that the variable noon‐midnight electric field can explain the fast development and inward transport of the transient electron belt extension observed in 2016.…”

Section: Introductionmentioning

confidence: 91%

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Sustaining Saturn's Electron Radiation Belts Through Episodic, Global‐Scale Relativistic Electron Flux Enhancements

et al. 2020

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The L shell distributions of MeV electrons in Saturn's radiation belt are investigated orbit by orbit for the 13-year exploration of Cassini. It is found that in addition to the monotonic decrease profiles, there are orbits showing superimposed transient extensions. The extensions are found to stand out above the background population during 50% of belt crossings. We estimate that there is high probability (>72%) that transient extensions contribute more than 10% electron content in the radiation belt. The high occurrence frequency of one extension every 2-3 weeks, together with the relative content, demonstrate that the extensions constitute a regular and fundamental process populating and sustaining the electron belts of Saturn. The transients regularity excludes interplanetary coronal mass ejections as dominant trigger and implies corotation interaction regions and/or internal processes as candidates. Statistical results suggest that the communication of electrons between the middle magnetosphere and the radiation belts is largely through convective radial transport, which produces transient radiation belt extensions. Plain Language SummaryThe electrons with velocities comparable to light speed residing in Saturn's magnetosphere, namely its electron radiation belt, are highly variable. One prominent feature of this variability is that the shape of permanently trapped population can be severely distorted by episodic, global-scale enhancements. A case study suggested that such an enhancement can be rapidly transmitted from large distances to the radiation belts by global-scale flows. These flows act on electrons in a similar manner engine impulses propel a spacecraft on a different orbit around a celestial body. It is of interest the role played by these enhancements on the evolution of the radiation belt, and which dynamic processes are responsible. In this study, enhancements are sought in the radial distributions of radiation belt electrons for the full, 13-year exploration of Cassini spacecraft. It is demonstrated that these enhancements constitute a regular and fundamental process that populates and sustains the radiation belts of Saturn. The enhancements' regularity implies periodic solar wind perturbations and/or internal magnetospheric dynamics as their major triggers. Among the large number of enhancements analyzed, we find evidence for several traveling radially inward, supporting the scenario that electrons are transported from large distances under the influence of global-scale flows.

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Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 91%

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Sustaining Saturn's Electron Radiation Belts Through Episodic, Global‐Scale Relativistic Electron Flux Enhancements

et al. 2020

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“…The time scale of 1 year in the simulations of Woodfield et al (2018) is probably too long. In fact, Roussos, Kollmann, Krupp, Paranicas, et al (2018), Yuan et al (2020) and Hao et al (2020) suggest relativistic electrons have residence time of the order of few days, due to the prevalence of Saturn's noon-midnight electric field all the way down to the planet's rings (Roussos et al, 2019;Paranicas, Mitchell, Roussos, et al, 2010), at least for the electrons measured by channels E4 and E6. However, the 100s-of-day time scale estimated by Woodfield et al (2018) was based on an initial condition that assumes a power-law electron spectrum with very low intensity at L < 4RS, while we see that the adiabatic heating from larger distances, may already provide a pre-accelerated electron distribution from which electrons are further heated to ultrarelativistic energies over shorter intervals.…”

Section: Accepted Articlementioning

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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“…The C22 event is morphologically similar to the enhancement of MeV electrons, i.e., transient extensions, frequently observed in the Kronian electron radiation belt (Roussos et al, 2018; Yuan et al, 2020). Roussos et al (2018), Hao et al (2020), Sun et al (2019) and Yuan et al (2020) proposed that a potential mechanism for the transient extensions is an energy dependent adiabatic acceleration associated with convective transport, due to large‐scale noon‐midnight electric fields in Saturn's magnetosphere (Paranicas et al, 2010; Thomsen et al, 2012; Andriopoulou et al, 2012, 2014). The existence of a similar large‐scale electric field in Jupiter's magnetosphere, albeit in the dawn‐dusk direction, has been inferred from the local time (LT) asymmetry of extreme ultraviolet (EUV) emissions of the Io plasma torus (IPT) (Barbosa & Kivelson, 1983; Ip & Goertz, 1983; Murakami et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Large-scale episodic enhancements of relativistic electron intensities in Jupiter's radiation belt

Yuan

Zuo

Roussos

et al. 2021

Earth and Planetary Physics

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Previous studies indicate that, in the Jovian magnetosphere, the long‐term trend of the radial profile of relativistic electron intensities is primarily shaped by slow radial diffusion. However, measurements by the Galileo spacecraft reveal the existence of transient increases in MeV electron intensities well above the ambient distribution. It is unclear how common such transient enhancements are, and to which dynamic processes in Jupiter's magnetosphere their occurrence is linked. We investigate the radial distributions of >11 MeV and >1 MeV electron intensities from 9RJ to 40RJ(RJ=71492 km denotes the Jovian radius), measured by the Galileo spacecraft from 1996 to 2002. We find transient enhancements of MeV electrons during seven Galileo crossings, mostly occurring around ∼20RJ. An apparent dawn‐dusk asymmetry of their occurrence is resolved, with a majority of events discovered at dawn. This dawn‐dusk asymmetry, as well as the average recurrence time scale of a few days, implies a potential relationship between the MeV electron transients and the storm‐like dynamics in the middle and outer magnetosphere detected using a variety of Galileo, Juno and remote sensing aurora observations. We suggest that the observations of some of these transients in the inner magnetosphere may result from a synergy between the convective transport by a large‐scale dawn‐dusk electric field and the sources provided by injections in the middle magnetosphere.

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

Cited by 14 publications

References 35 publications

Sustaining Saturn's Electron Radiation Belts Through Episodic, Global‐Scale Relativistic Electron Flux Enhancements

Sustaining Saturn's Electron Radiation Belts Through Episodic, Global‐Scale Relativistic Electron Flux Enhancements

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

Large-scale episodic enhancements of relativistic electron intensities in Jupiter's radiation belt

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