Chorus, ECH, and Z mode emissions observed at Jupiter and Saturn and possible electron acceleration

Menietti, J. D.; Shprits, Y. Y.; Horne, Richard B.; Woodfield, E. E.; Hospodarsky, G. B.; Gurnett, D. A.

doi:10.1029/2012ja018187

Cited by 56 publications

(52 citation statements)

References 102 publications

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“…Menietti et al . [, ] reported a similar decrease of chorus intensity and bandwidth near the magnetic equator for Saturn chorus emissions. Summers et al .…”

Section: Introductionsupporting

confidence: 53%

Saturn chorus intensity variations

et al. 2013

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[1] Whistler mode chorus plasma wave emissions have been observed at Saturn near the magnetic equator and the source region. During crossings of the magnetic equator along nearly constant L shells, the Cassini Radio and Plasma Wave Science Investigation often observes a local decrease in whistler mode intensity and bandwidth closest to the magnetic equator, where linear growth appears to dominate, with nonlinear structures appearing at higher latitudes and higher frequencies. We investigate linear growth rate using the Waves in a Homogeneous, Anisotropic, Multi-component Plasma dispersion solver and locally observed electron phase space density measurements from the Electron Spectrometer sensor of the Cassini Plasma Spectrometer Investigation to determine the parameters responsible for the variation in chorus intensity and bandwidth. We find that a temperature anisotropy (T ⊥ /T ∥~1 .3) can account for linear spatiotemporal growth rate of whistler mode waves, which provides a majority of the observed frequency-integrated power. At the highest frequencies, intense, nonlinear, frequency-drifting structures (drift rates~200 Hz/s) are observed a few degrees away from the equator and can account for a significant fraction of the total power. Chorus emission at higher frequencies is distinct from lower frequency whistler mode emission and is sometimes correlated with simultaneously observed low-frequency electromagnetic ion cyclotron waves. These electromagnetic ion cyclotron waves appear to modulate a slow frequency drift (~15 Hz/s) which develops into nonlinear growth with much larger frequency drift associated only with the higher-frequency chorus.

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“…Menietti et al . [, ] reported a similar decrease of chorus intensity and bandwidth near the magnetic equator for Saturn chorus emissions. Summers et al .…”

Section: Introductionsupporting

confidence: 53%

Saturn chorus intensity variations

et al. 2013

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“…The orbit of Galileo was such that it covered regions close to the magnetic equator, but the quantity of wave data falls off dramatically at latitudes λ 10 • . Evidence from both the Earth and Saturn, where chorus is observed up to 45 • (Meredith et al, 2012;Bunch et al, 2012;Menietti et al, 2012), suggest that chorus may be present at Jupiter far from the equator.…”

Section: Calculating Diffusion Coefficientsmentioning

confidence: 99%

“…At Jupiter wave observations have only been made for latitudes 10 • in the region outside Io; previous work to calculate the electron acceleration due to chorus waves assumed the waves only extended to 10 • . However, observations at Earth and Saturn show that waves are observed up to latitudes of 45 • (Meredith et al, 2001(Meredith et al, , 2012Bunch et al, 2012;Menietti et al, 2012). Since the plasma density drops significantly with increasing latitude (Bagenal, 1994), the conditions for acceleration may be more favorable at higher latitudes.…”

Section: Introductionmentioning

confidence: 99%

Electron acceleration at Jupiter: input from cyclotron-resonant interaction with whistler-mode chorus waves

et al. 2013

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Abstract. Jupiter has the most intense radiation belts of all the outer planets. It is not yet known how electrons can be accelerated to energies of 10 MeV or more. It has been suggested that cyclotron-resonant wave-particle interactions by chorus waves could accelerate electrons to a few MeV near the orbit of Io. Here we use the chorus wave intensities observed by the Galileo spacecraft to calculate the changes in electron flux as a result of pitch angle and energy diffusion. We show that, when the bandwidth of the waves and its variation with L are taken into account, pitch angle and energy diffusion due to chorus waves is a factor of 8 larger at Lshells greater than 10 than previously shown. We have used the latitudinal wave intensity profile from Galileo data to model the time evolution of the electron flux using the British Antarctic Survey Radiation Belt (BAS) model. This profile confines intense chorus waves near the magnetic equator with a peak intensity at ∼ 5 • latitude. Electron fluxes in the BAS model increase by an order of magnitude for energies around 3 MeV. Extending our results to L = 14 shows that cyclotron-resonant interactions with chorus waves are equally important for electron acceleration beyond L = 10. These results suggest that there is significant electron acceleration by cyclotron-resonant interactions at Jupiter contributing to the creation of Jupiter's radiation belts and also increasing the range of L-shells over which this mechanism should be considered.

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“…The typical frequency range of chorus is several hundreds of hertz to several kilohertz [cf. Menietti et al ., 2008, Figure 2; Menietti et al ., , Figure 3]. The free energy source of this chorus may be associated with warm plasma within inward convecting magnetic flux tubes associated with the interchange instability in a corotation‐dominated magnetosphere [ Hill et al ., ; Pontius et al ., ; Thorne et al ., ; Bolton et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Survey of whistler mode chorus intensity at Jupiter

et al. 2016

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Whistler mode chorus emission is important in the acceleration of electrons and filling of the radiation belts at Jupiter. In this work chorus magnetic intensity levels (frequency‐integrated spectral density, PB) at Jupiter are comprehensively binned and parameterized. The frequency range of chorus under study extends from the lower hybrid frequency, flh, to fceq/2 and fceq/2 < f < 0.8 fceq, where fceq is the cyclotron frequency mapped to the magnetic equator. The goal is to obtain a quantized distribution of magnetic intensity for use in stochastic modeling efforts. Parametric fits of magnetic plasma wave intensity are obtained, including PB versus frequency, latitude, and L shell. The results indicate that Jupiter chorus occurrence probability and intensity are higher than those at Saturn, reaching values observed at Earth. Jovian chorus is observed over most local times, confined primarily to the range 8 < L < 15, outside the high densities of the Io torus. The largest intensity levels are seen on the dayside; however, the sampling of chorus on the nightside is much less than on the dayside. Peak intensities occur near the equator with a weak dependence on magnetic latitude, λ. We conclude that Jovian chorus average intensity levels are approximately an order of magnitude lower than those at Earth. In more isolated regions the intensities are comparable to those observed at Earth. The spatial range of the chorus emissions extends beyond that assumed in previous Jovian global diffusive models of wave‐particle electron acceleration.

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Chorus, ECH, and Z mode emissions observed at Jupiter and Saturn and possible electron acceleration

Cited by 56 publications

References 102 publications

Saturn chorus intensity variations

Saturn chorus intensity variations

Electron acceleration at Jupiter: input from cyclotron-resonant interaction with whistler-mode chorus waves

Survey of whistler mode chorus intensity at Jupiter

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