Properties of Jupiter's magnetospheric turbulence observed by the Galileo spacecraft

Tao, Chihiro; Sahraoui, Fouad; Fontaine, Dominique; Patoul, Judith de; Chust, T.; Kasahara, Satoshi; Retinò, Alessandro

doi:10.1002/2014ja020749

Cited by 50 publications

(75 citation statements)

References 66 publications

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“…The perturbation of the magnetic field is then δ B ( t ) = B ( t ) − B 0 , and perpendicular fluctuations of the magnetic field are given by δ B ( t ) ⊥ = δ B ( t ) − δ B ( t ) ∥ , where δ B ( t ) ∥ is the component of the fluctuation of the magnetic field parallel to B 0 . The power spectrum of vector components of δ B ( t ) ⊥ is then estimated as in Tao et al []:

P (f) = \frac{2}{NΔt} \sum_{i = 1}^{N} Δt {(||, W_{i} (t_{i}, f))}^{2}

where W i ( t i , f ) is a Morlet wavelet with the period of (1.03 f ) 1 [ Farge , ; Torrence and Compo , ]. The total power spectrum of the perpendicular fluctuation is calculated as the square root of the sum of the squares of the components.…”

Section: Discussionmentioning

confidence: 99%

Local time dependence of turbulent magnetic fields in Saturn's magnetodisc

Kaminker

Delamere

et al. 2017

JGR Space Physics

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Net plasma transport in magnetodiscs around giant planets is outward. Observations of plasma temperature have shown that the expanding plasma is heating nonadiabatically during this process. Turbulence has been suggested as a source of heating. However, the mechanism and distribution of magnetic fluctuations in giant magnetospheres are poorly understood. In this study we attempt to quantify the radial and local time dependence of fluctuating magnetic field signatures that are suggestive of turbulence, quantifying the fluctuations in terms of a plasma heating rate density. In addition, the inferred heating rate density is correlated with magnetic field configurations that include azimuthal bend forward/back and magnitude of the equatorial normal component of magnetic field relative to the dipole. We find a significant local time dependence in magnetic fluctuations that is consistent with flux transport triggered in the subsolar and dusk sectors due to magnetodisc reconnection.

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P (f) = \frac{2}{NΔt} \sum_{i = 1}^{N} Δt {(||, W_{i} (t_{i}, f))}^{2}

Section: Discussionmentioning

confidence: 99%

Local time dependence of turbulent magnetic fields in Saturn's magnetodisc

Kaminker

Delamere

et al. 2017

JGR Space Physics

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“…During this time interval, the spacecraft traversed from the magnetic pileup region to the magnetosheath and finally into the upstream region (see Figure d). Performing a wavelet transform on the magnetic field time series as in Tao et al [], we compute power spectral densities (PSDs) for the magnetic field fluctuations (see Figure c):

normalPSD (f) = \frac{2 Δt}{N} \sum_{j = 1}^{N} | W_{x} (t_{j}, f) |^{2} + | W_{y} (t_{j}, f) |^{2} + | W_{z} (t_{j}, f) |^{2},

where W x , W y , and W z are the wavelet transforms of the x , y , and z MSO components of the magnetic field. Here Δ t is the inverse sampling rate of the magnetometer.…”

Section: Methodsmentioning

confidence: 99%

“…Turbulence in these plasma environments shows both similarities and differences with that of the solar wind turbulence. In particular, similar to the solar wind, magnetic field fluctuations in these plasma environments display different spectral indices in different frequency ranges [ Zimbardo et al , ; Hadid et al , ; Tao et al , ]. However, the spectral index in a given frequency range has different values in different regions of a given plasma environment [ Zimbardo et al , ].…”

Section: Introductionmentioning

confidence: 99%

“…For example, Hadid et al [] observed that, in the magnetosheath of Saturn, the spectral index changes from a value of approximately −1.2 at low frequencies to a value of approximately −2.5 at high frequencies (frequencies higher than the proton gyrofrequency) without forming the intermediate inertial range that has the Kolmogorov scaling value, unlike in the solar wind. The absence of the inertial range has also been observed at the Earth's magnetosheath and Jupiter's magnetosphere [ Zimbardo et al , ; Tao et al , ]. However, the absence of the frequency range with the Kolmogorov scaling value is not a universal feature in planetary plasma environments.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of turbulence in the Mars plasma environment with MAVEN observations

et al. 2017

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We characterize turbulence in the Mars plasma environment in a global scale for the first time by computing spectral indices for magnetic field fluctuations (slopes in the magnetic field power spectra) and determining how they vary with frequency and in different regions. In the magnetosheath, unlike in the solar wind, we find an absence of the inertial range which has a spectral index value equal to the Kolmogorov scaling value of −5/3. Instead, as observed in the magnetosheaths of other planets, we find that the spectral indices transition from low negative values close to −0.5 at low frequencies (< proton gyrofrequency) to values much lower than −5/3 at high frequencies (> proton gyrofrequency). This indicates that the pristine solar wind is modified at the Martian bow shock and that the fluctuations are dominated by locally generated fluctuations in the magnetosheath. The absence of spectral indices with the Kolmogorov scaling value indicates that the fluctuations in the magnetosheath do not have sufficient time to interact with one another leading to a fully developed energy cascade. Spectral index values near the Kolmogorov scaling value are observed for the low‐frequency range near the magnetic pileup boundary, and this indicates the presence of fully developed energy cascade. In the wake, we find that the spectral indices have approximately the same values, typically near −2, for both the low‐ and high‐frequency ranges. We observe seasonal variations of the spectral indices, mainly in the upstream region, which indicate the seasonal variations of the proton cyclotron waves.

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“…These velocities can be determined using an empirically fitted radial profile (Thomsen et al, ). For a given 1‐s‐averaged MAG time series, the one‐dimensional power spectrum

P false(f false)

δ B_{⊥}

is calculated with a Morlet wavelet transform (Tao et al, ). Similarly to section ,

{false(P false(f false) f false)}^{3 false/ 2} \sim δ B_{⊥}^{2}

is integrated with a factor

k_{⊥}

, as in equation .…”

Section: Disturbed Magnetic Fields Near Saturn's Magnetopausementioning

confidence: 99%

Identifying Active Kelvin–Helmholtz Vortices on Saturn's Magnetopause Boundary

Burkholder

Delamere

2020

Geophysical Research Letters

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For ∼2,000 Cassini magnetopause encounters, we analyse plasma and magnetic fields. The boundary can be unstable to the Kelvin–Helmholtz instability (KHI), which can drive large‐scale flows identifiable in plasma measurements. Bulk flow reversed from the expected direction near the magnetopause can indicate vorticity associated with active KH, and events are found dominantly in the dawn–subsolar region. KHIs are also responsible for magnetic field fluctuations, and hybrid simulations indicate heating, and transport is significant in an actively growing vortex. Cassini observations are filtered for disturbed magnetic fields near the magnetopause, similar to the signatures from hybrid simulations, with significant fluctuation and current sheet crossings. We also find that these occur most frequently in the dawn–subsolar region. A turbulent heating rate density and mass diffusion coefficient are calculated for these disturbed events and compared with the hybrid simulation to test whether enhanced values for these quantities can identify active KH events.

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Properties of Jupiter's magnetospheric turbulence observed by the Galileo spacecraft

Cited by 50 publications

References 66 publications

Local time dependence of turbulent magnetic fields in Saturn's magnetodisc

Local time dependence of turbulent magnetic fields in Saturn's magnetodisc

Characterization of turbulence in the Mars plasma environment with MAVEN observations

Identifying Active Kelvin–Helmholtz Vortices on Saturn's Magnetopause Boundary

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