Source mechanism of Saturn narrowband emission

Menietti, J. D.; Yoon, Peter H.; Ye, Shengyi; Cecconi, Baptiste; Rymer, A. M.

doi:10.5194/angeo-28-1013-2010

Cited by 15 publications

(21 citation statements)

References 28 publications

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“…Z mode emission at Saturn is observed associated with narrowband emission as discussed by Ye et al [2010]. The clearest examples are the 5 kHz narrowband emission as shown in Figure 9, but Z mode is also associated with upper hybrid emission near strong density gradients and source regions of 20 kHz narrowband emission as discussed by Menietti et al [2009, 2010]. In Figure 9 narrowband emission near 5 kHz is seen both above and below f c .…”

Section: Saturn Chorus Observationsmentioning

confidence: 73%

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

Menietti¹,

Shprits²,

Horne³

et al. 2012

J. Geophys. Res.

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In this paper we compare and contrast chorus, electron cyclotron harmonics (ECH), and Z mode emissions observed at Jupiter and Saturn and relate them to recent work on electron acceleration at Earth. Intense chorus emissions are observed near the magnetic equator, the likely source region, but the strongest intensities are on either side of the magnetic equator. Chorus intensities at Jupiter are generally about an order of magnitude larger than at Saturn, and the bandwidth of chorus at Jupiter can reach 7 or 8 kHz (∼0.6 fc), while at Saturn it is typically <2 kHz (∼0.6 fc, also). No higher‐latitude information is available at Jupiter; however, high inclination orbits at Saturn by Cassini reveal strong chorus intensities at latitudes extending to over 30°. At Jupiter, initial studies reveal the chorus intensities are sufficient to accelerate electrons by a stochastic process; however, the high density levels near the source region of chorus at Saturn indicate a less efficient process except for local regions such as within plasma injection regions. The role of Z mode in electron acceleration and the role of ECH waves in pitch angle scattering at both Jupiter and Saturn require further study.

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Section: Saturn Chorus Observationsmentioning

confidence: 73%

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

Menietti¹,

Shprits²,

Horne³

et al. 2012

J. Geophys. Res.

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“…Computation of growth rate for Z mode waves by Menietti et al . [, , ] also indicated that Z mode waves have very large normal angles. In this study, we assume that the wave normal angle distribution of Z mode waves is Gaussian with a peak at 89°, which is described as follows [e.g., Glauert and Horne , ; Ni et al ., ]:

g (X) = {\begin{cases} left & exp (- {((), \frac{X - X_{m}}{X_{w}})}^{2}) & X_{min} \leq X \leq X_{max} \\ left & 0 & otherwise \end{cases},

where X = tan( θ ) with θ as the wave normal angle, X m (=tan θ m ) is the peak, X w (=tan θ w ) is the angle width, and X min (=tan θ min ) and X max (=tan θ max ) are the lower and upper cutoff.…”

Section: Modelsmentioning

confidence: 99%

Resonant diffusion of energetic electrons by narrowband Z mode waves in Saturn's inner magnetosphere

Thorne

et al. 2013

Geophysical Research Letters

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[1] Banded emissions near 5 and 20 kHz are observed by the Cassini Radio and Plasma Wave Science (RPWS) instrument and are identified as Z mode waves in the regions where the plasma frequency is below the electron gyrofrequency. Using wave parameters derived from Gaussian fits to the measured power spectral density for narrow-band Z mode waves and the ambient density and magnetic field information at L =~4, we compute the bounce-averaged diffusion coefficients for the Saturnian radiation belt electrons. Our results indicate that 5 kHz Z mode emissions can cause resonant scattering of electrons from~2 MeV to tens of megaelectron volts, while 20 kHz waves can interact with electrons from hundreds of kiloelectron volts to~2 MeV. In principle, the rate of momentum diffusion can be an order of magnitude larger than that of pitch angle diffusion and cross diffusion for electrons at equatorial pitch angles >~10 , suggesting that Z mode waves on Saturn are responsible for local acceleration of radiation belt energetic electrons at intermediate pitch angles. Citation: Gu, X., R. M. Thorne, B.Ni, and S.-Y. Ye (2013), Resonant diffusion of energetic electrons by narrowband Z mode waves in Saturn's inner magnetosphere, Geophys. Res. Lett., 40,[255][256][257][258][259][260][261]

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“…Although the energy source for the generation of the Z-mode waves is still unclear, linear growth rate calculations indicate that the observed plasma distributions are unstable to the growth of electrostatic cyclotron harmonic emission. Electromagnetic Z-mode could also be directly generated by the cyclotron maser instability Menietti et al, 2010]. (6) Similar to SKR, the 5 kHz NB emissions have a clock-like source and display two distinct modulation periods identical to the northern and southern hemisphere periods of SKR [Ye et al, 2010b].…”

Section: Resultsmentioning

confidence: 99%

“…f UH ∼ = nf ce Menietti et al, 2010]. These Z-mode waves can then mode convert to L-O mode on a density gradient or density irregularities.…”

Section: Source Mechanismmentioning

confidence: 99%

An Overview of Saturn Narrowband Radio Emissions Observed by Cassini RPWS (invited)

Ye¹,

Fischer²,

Menietti³

et al. 2011

Planetary Radio Emissions Vii

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Saturn narrowband (NB) radio emissions are detected between 3 and 70 kHz, with occurrence probability and wave intensity peaking around 5 kHz and 20 kHz. The emissions usually occur periodically for several days after intensification of Saturn kilometric radiation (SKR). Originally detected by the Voyagers, the extended duration of the Cassini mission and the improved capabilities of the Radio and Plasma Wave Science (RPWS) instrument have significantly advanced our knowledge about them. For example, RPWS measurements of the magnetic component have validated the electromagnetic nature of Saturn NB emissions. Evidences show that the 20 kHz NB emissions are generated by mode conversion of electrostatic upper hybrid waves on the boundary of the plasma torus, whereas direction-finding results point to a source in the auroral zone for the 5 kHz component. Similar to SKR, the 5 kHz NB emissions have a clock-like modulation and display two distinct modulation periods identical to the northern and southern hemisphere periods of SKR. Polarization measurements confirm that most NB emissions are propagating in the L-O mode, with the exception of second harmonic NB emissions. At high latitudes closer to the planet, RPWS detected right hand polarized Z-mode NB emissions below the local electron cyclotron frequency (f ce ), which are believed to be the source of the L-O mode NB emissions detected above the local f ce . Although the energy source for the generation of the Z-mode waves is still unclear, linear growth rate calculations indicate that the observed plasma distributions are unstable to the growth of electrostatic cyclotron harmonic emission. Alternatively, electromagnetic Z-mode might be directly generated by the cyclotron maser instability. The source Z-mode waves, upon reflection, propagate to the opposite hemisphere before escaping through mode conversion, which could explain the fact that both rotational modulation periods of NB emissions are observable in each hemisphere.

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Source mechanism of Saturn narrowband emission

Cited by 15 publications

References 28 publications

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

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

Resonant diffusion of energetic electrons by narrowband Z mode waves in Saturn's inner magnetosphere

An Overview of Saturn Narrowband Radio Emissions Observed by Cassini RPWS (invited)

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