Standing Alfvén Waves in Jupiter's Magnetosphere as a Source of ∼10‐ to 60‐Min Quasiperiodic Pulsations

Manners, Harry; Masters, A.; Yates, J. N.

doi:10.1029/2018gl078891

Cited by 22 publications

(46 citation statements)

References 55 publications

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“…The periodic oscillations from ULF waves have been observed throughout the Jovian magnetosphere. Manners et al () propose that all

\sim

10‐ to 60‐min QPOs within the Jovian magnetosphere may arise from standing Alfvén waves. This complements the work of Khurana and Kivelson () and Wilson and Dougherty () who found 10‐ to 20‐min ULF wave pulsations in the middle magnetosphere.…”

Section: Discussionmentioning

confidence: 99%

Chandra Observations of Jupiter's X‐ray Auroral Emission During Juno Apojove 2017

et al. 2020

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Jupiter's auroral X-rays have been observed for 40 years with an unknown driver producing quasiperiodic emission, concentrated into auroral hot spots. In this study we analyze an ∼ 10-hr Chandra observation from 18:56 on 18 June 2017. We use a new Python pipeline to analyze the auroral morphology, perform timing analysis by incorporating Rayleigh testing, and use in situ Juno observations to infer the magnetosphere that was compressed during the Chandra interval. During this time Juno was near its apojove position of ∼112 R J , on the dawn flank of the magnetosphere near the nominal magnetopause position. We present new dynamical polar plots showing an extended X-ray hot spot in the northern auroral region traversing across the Jovian disk. From this morphology, we propose setting a numerical threshold of >7 photons per 5 • System III longitude × 5 • latitude to define a photon concentration of the northern hot spot region. Our timing analysis finds two significant quasiperiodic oscillations (QPOs) of ∼37 and ∼26 min within the extended northern hot spot. No statistically significant QPOs were found in the southern X-ray auroral emission. The Rayleigh test is combined with Monte Carlo simulation to find the statistical significance of any QPOs found. We use a flux equivalence mapping model to trace the possible origin of the QPOs, and thus the driver, to the dayside magnetopause boundary.

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“…The periodic oscillations from ULF waves have been observed throughout the Jovian magnetosphere. Manners et al () propose that all

\sim

Section: Discussionmentioning

confidence: 99%

Chandra Observations of Jupiter's X‐ray Auroral Emission During Juno Apojove 2017

et al. 2020

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“…However, if this periodicity originated in the solar wind, it is unclear how it would be preserved traveling across Jupiter's bow shock and magnetosheath. Another explanation could involve ultralow frequency (ULF) waves that have been measured to have periods of ∼10 min (Dunn et al, , ; Khurana & Kivelson, ; Manners et al, ; Manners & Masters, ). The frequencies of ULF waves depend on the length and the mass content of the perturbed field line.…”

Section: Discussionmentioning

confidence: 99%

Temporal and Spectral Studies by XMM‐Newton of Jupiter's X‐ray Auroras During a Compression Event

et al. 2020

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We report the temporal and spectral results of the first XMM-Newton observation of Jupiter's X-ray auroras during a clear magnetospheric compression event on June 2017 as confirmed by data from the Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno. The northern and southern auroras were visible twice and thrice respectively as they rotated in and out of view during the ∼23-hr (almost 2.5 Jupiter rotations) long XMM-Newton Jovian-observing campaign. Previous auroral observations by Chandra and XMM-Newton have shown that the X-ray auroras sometimes pulse with a regular period. We applied wavelet and fast Fourier transforms (FFTs) on the auroral light curves to show that, following the compression event, the X-ray auroras exhibited a recurring 23-to 27-min periodicity that lasted over 12.5 hr (longer than a Jupiter rotation). This periodicity was observed from both the northern and southern auroras, suggesting that the emission from both poles was caused by a shared driver. The soft X-ray component of the auroras is due to charge exchange processes between precipitating ions and neutrals in Jupiter's atmosphere. We utilized the Atomic Charge Exchange (ACX) spectral package to produce solar wind and iogenic plasma models to fit the auroral spectra in order to identify the origins of these ions. For this observation, the iogenic model gave the best fit, which suggests that the precipitating ions are from iogenic plasma in Jupiter's magnetosphere. Plain Language SummaryThe solar wind is a continuous stream of charged particles released by the Sun that flows out toward the edge of the Solar System. It meets obstacles along the way, such as the magnetic fields of planets like the Earth to create a magnetic bubble around them called a magnetosphere. The magnetosphere prevents most of these charged particles from reaching the Earth's atmosphere. Those that make their way through interact with the gas molecules in the atmosphere above the polar regions and cause them to glow to produce the auroras or the northern and southern lights. Jupiter's auroras are much more powerful than the Earth's, and they emit different types of radiation, including X-rays. It is currently unclear as to what causes Jupiter's X-ray auroras. Its moon, Io, spews volcanic material into the magnetosphere that can be accelerated into the planet's atmosphere. We created models that consisted of the particles found in the solar wind and in the material from Io's volcanoes to see which one was responsible for Jupiter's X-ray auroras. In this case, it was Io's volcanoes. We also found that the auroras pulsate every ∼23-27 min in the north and ∼23-33 min in the south.

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“…The magnetic perturbations fields of interest are typically of order ∼1 nT. To inspect these small‐amplitude perturbations, we rotated the data into the mean‐field‐aligned (MFA) coordinate system outlined in Manners et al (), which uses a sliding average window of width 60 min to produce a principal unit vector

{\overset{b}{true}}_{false| false|}

aligned with the average background magnetic field. The unit vectors

{\overset{b}{true}}_{⊥, 1}

and

{\overset{b}{true}}_{⊥, 2}

complete the right‐handed orthogonal set and are transverse to the mean field.…”

Section: Searching For Ulf Waves In Jupiter's Magnetospherementioning

confidence: 99%

“…To compare the decomposed signals with predicted standing Alfvén wave harmonics, we refer to a magnetospheric box model previously adapted for the Jovian magnetosphere (Khurana & Kivelson, ; Manners et al, ; Southwood & Kivelson, ). As each field line acts as a linear resonator with an independent set of harmonic periods, the model uses a 1‐D model field line to solve for the field‐line eigenperiods, parametrized by the Alfvén speed inside the plasma sheet, and the sheet half thickness.…”

Section: First Evidence For Multiple‐harmonic Standing Alfvén Waves Imentioning

confidence: 99%

“…The combination of these effects results in the MHD wave power and standing wave nodal structure being effectively confined to the equatorial region. Recently, Manners et al () used the box model first presented by Kivelson and Southwood () to compare standing Alfvén wave eigenperiods to all of the QP ULF periods observed at Jupiter. They found that due to either spatial variation in plasma sheet properties or a superposition of harmonics on the same field line, standing Alfvén waves are consistent with the full range of observations.…”

Section: Introductionmentioning

confidence: 99%

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First Evidence for Multiple‐Harmonic Standing Alfvén Waves in Jupiter's Equatorial Plasma Sheet

Manners

Masters

2019

Geophysical Research Letters

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Quasiperiodic pulsations in the ultralow‐frequency band are ubiquitously observed in the Jovian magnetosphere, but their source and distribution have until now been a mystery. Standing Alfvén waves on magnetic field lines have been proposed to explain these pulsations and their large range in observed periods. However, in situ evidence in support of this mechanism has been scarce. Here we use magnetometer data from the Galileo spacecraft to report first evidence of a multiple‐harmonic ultralow‐frequency event in Jupiter's equatorial plasma sheet. The harmonic periods lie in the 4‐ to 22‐min range, and the nodal structure is confined to the plasma sheet. Polarization analysis reveals several elliptically polarized odd harmonics and no presence of even harmonics. The harmonic periods, their polarization, and the confinement of the wave to the plasma sheet are strong evidence supporting the standing Alfvén wave model. Multiple‐harmonic waves therefore potentially explain the full range of periods in quasiperiodic pulsations in Jupiter's magnetosphere.

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Standing Alfvén Waves in Jupiter's Magnetosphere as a Source of ∼10‐ to 60‐Min Quasiperiodic Pulsations

Cited by 22 publications

References 55 publications

Chandra Observations of Jupiter's X‐ray Auroral Emission During Juno Apojove 2017

Chandra Observations of Jupiter's X‐ray Auroral Emission During Juno Apojove 2017

Temporal and Spectral Studies by XMM‐Newton of Jupiter's X‐ray Auroras During a Compression Event

First Evidence for Multiple‐Harmonic Standing Alfvén Waves in Jupiter's Equatorial Plasma Sheet

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