Gyro-resonant electron acceleration at Jupiter

Horne, Richard B.; Thorne, R. M.; Glauert, S. A.; Menietti, J. D.; Shprits, Y. Y.; Gurnett, D. A.

doi:10.1038/nphys897

Cited by 90 publications

(135 citation statements)

References 24 publications

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“…Recently, Horne et al [2008] demonstrated that interactions between electrons and whistler mode waves in the Jovian magnetosphere cause significant acceleration of MeV electrons on a time scale of 30 days. Using wave power spectral density from Galileo measurements, Horne et al [2008] calculated quasi-linear pitch angle and energy diffusion coefficients and solved a two dimensional diffusion equation at 10 R J . They showed that fluxes of 1-6 MeV electrons increased by more than an order of magnitude within 30 days.…”

Section: Introductionmentioning

confidence: 99%

“…[4] In the calculation of Horne et al [2008], an empirical electron density model was used in calculation of diffusion coefficients. The empirical electron density model, however, does not consider the observed density decrease within plasma injection regions.…”

Section: Introductionmentioning

confidence: 99%

“…Horne et al [2008] assumed that the wave power peaks around wave normal angle y = 0°, based on previous studies on terrestrial whistler mode chorus waves [Horne et al, 2005a;Li et al, 2007]. However, several ray tracing studies and observations have shown that whistler waves tend to become more oblique at higher latitudes even when starting parallel from the equator Li et al, 2008Li et al, , 2009Haque et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

“…[6] In this work, we follow the modeling of Horne et al [2008], but also take into consideration cross diffusion terms D ap , which have been shown to be important for quantifying wave particle interactions in the terrestrial magnetosphere [Albert and Young, 2005;Tao et al, 2008Tao et al, , 2009Xiao et al, 2009]. The sensitivity of the main conclusions of Horne et al [2008] to the amount of density decrease inside the local plasma injection regions is analyzed in section 3.2.…”

Section: Introductionmentioning

confidence: 99%

“…The sensitivity of the main conclusions of Horne et al [2008] to the amount of density decrease inside the local plasma injection regions is analyzed in section 3.2. A ray tracing code HOTRAY [Horne, 1989] is then used to trace several whistler wave rays from the equator to higher latitudes to investigate change of their wave normal angle.…”

Section: Introductionmentioning

confidence: 99%

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Importance of plasma injection events for energization of relativistic electrons in the Jovian magnetosphere

et al. 2011

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[1] Effects of density decrease in plasma injection regions and a latitude-dependent wave normal angle distribution on the energization of electrons by whistler mode waves at Jupiter are investigated. Previous work showed that whistler mode waves could enhance the fluxes of a few MeV electrons by an order of magnitude on a time scale of 30 days. However, density decrease in plasma injection regions and latitude dependence of the wave normal angle distribution of waves were not considered. Because this information is difficult to obtain from available observations, we perform a sensitivity study to demonstrate that the effect of density decrease on energization of electrons becomes important when the density inside injection regions is reduced to 25% of that outside. We also investigate the effect of a latitude-dependent wave normal angle distribution on energization of electrons using a ray tracing program and demonstrate that a realistic latitude-dependent wave normal angle distribution increases the rate of pitch angle diffusion near the loss cone, and thus enhances the loss rate, of 1-3 MeV electrons. However, the flux of 10 MeV electrons is not significantly affected. Results of the work are useful for understanding energization of MeV electrons at Jupiter, especially when combined with observations from future missions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Importance of plasma injection events for energization of relativistic electrons in the Jovian magnetosphere

et al. 2011

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The origin of Jupiter's outer radiation belt

et al. 2014

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The intense inner radiation belt at Jupiter (>50 MeV at 1.5 R J ) is generally accepted to be created by radial diffusion of electrons from further away from the planet. However, this requires a source with energies that exceed 1 MeV outside the orbit of the moon Io at 5.9 R J , which has never been explained satisfactorily. Here we test the hypothesis that this source population could be formed from a very soft energy spectrum, by particle injection processes and resonant electron acceleration via whistler mode chorus waves. We use the British Antarctic Survey Radiation Belt Model to calculate the change in the electron flux between 6.5 and 15 R J ; these are the first simulations at Jupiter combining wave particle interactions and radial diffusion. The resulting electron flux at 100 keV and 1 MeV lies very close to the Galileo Interim Radiation Electron model spectrum after 1 and 10 days, respectively. The primary driver for the increase in the flux is cyclotron resonant acceleration by chorus waves. A peak in phase space density forms such that inside L ≈ 9 radial diffusion transports electrons toward Jupiter, but outside L ≈ 9 radial diffusion acts away from the planet. The results are insensitive to the softness of the initial energy spectrum but do depend on the value of the flux at the minimum energy boundary. We conclude by suggesting that the source population for the inner radiation belt at Jupiter could indeed be formed by wave-particle interactions.

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Saturn chorus latitudinal variations

et al. 2014

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The variation of propagation properties of whistler mode chorus as a function of latitude is not well known at Saturn but is important for the calculation of pitch angle diffusion and nonlinear growth of chorus. The Cassini spacecraft has spent a portion of its orbital time in high-inclination orbits, allowing traversal of the magnetic equator at nearly constant L shell for several passes. This is important since chorus is believed to propagate dominantly close to the magnetic field direction. We have investigated the change of wave normal angle, whistler mode magnetic intensity, and ambient magnetic field inhomogeneity as a function of latitude observed by the Radio and Plasma Wave investigation onboard the Cassini instrument. We find that wave normal angles along a nearly constant L shell remain close to field-aligned, except nearest the equator, and whistler mode wave intensity increases from the magnetic equator, according to a power law. The ambient magnetic field shows an inhomogeneity that is lower than Earth's, but there is a lack of drifting-frequency signatures nearest the equator. The bandwidth of the chorus emission can be described by a simple exponential. The bandwidth increases from the equator, peaking a few degrees away in a region of strong nonlinear growth and then decreases at higher latitudes.

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Gyro-resonant electron acceleration at Jupiter

Cited by 90 publications

References 24 publications

Importance of plasma injection events for energization of relativistic electrons in the Jovian magnetosphere

Importance of plasma injection events for energization of relativistic electrons in the Jovian magnetosphere

The origin of Jupiter's outer radiation belt

Saturn chorus latitudinal variations

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