Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

Martos, Yasmina M.; Imai, Masafumi; Connerney, J. E. P.; Kotsiaros, Stavros; Kurth, W. S.

doi:10.1029/2020je006415

Cited by 5 publications

(8 citation statements)

References 51 publications

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“…Importantly, our lead angle models placed the active IFT at δ ≤ 3° (see Figure 1). Our results thus significantly disagree with those of (Martos et al., 2020). Also, in their article, the authors stated that “ In any case, we produce better fits between our models and the observations than other recent studies (Louis et al., 2017) wherein the authors obtained models that yield arcs around 1–2 hr removed from the observation times as well as MHz of difference in frequency ”.…”

Section: Single‐point Radio Observations: Toward a Statistical Studycontrasting

confidence: 99%

“…It is worth adding two comments here. Firstly, the study of Martos et al (2020) is based on the fit of Io-DAM arcs, so that a good correspondence between the fit and the observed arc is a prerequisite of their analysis rather than a consequence of it. Secondly, the study of C. K. was based on the a priori modeling of Io-DAM arcs with the ExPRES code using constant electron energies, namely 0.64 keV in the north and 3 keV in the south and a simple sinusoidal lead angle model, following S. Hess et al (2008).…”

Section: Application To Case Studies Investigated In Other Recent Art...mentioning

confidence: 99%

“…Martos et al. (2020) developed a different method and applied it to one example of Io‐A, B, C, and D events (sometimes made of multiple arcs) as observed by Juno/Waves alone. To our understanding, their method combines fits of the position of the active IFT determined by an ionospheric lead angle and θ for each Io‐DAM arc, providing ranges for this pair of covariant quantities, thus large uncertainties in a blind unconstrained fit.…”

Section: Single‐point Radio Observations: Toward a Statistical Studymentioning

confidence: 99%

“…Applied to Wind/STEREO radio observations of a single Io-DAM event, the authors obtained θ(f) varying within ∼65 − 60° for δ ∼ 32°, leading to E e− ∼ 10 − 20 keV. Martos et al (2020) investigated 4 cases of Io-DAM events observed by Juno and jointly derived θ(f) and δ. They obtained highly variable values within ∼33-85° and ∼1-40°, respectively, leading to E e− ranging from 1 to 50 keV.…”

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confidence: 99%

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Determining the Beaming of Io Decametric Emissions: A Remote Diagnostic to Probe the Io‐Jupiter Interaction

et al. 2022

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We investigate the beaming of 11 Io‐Jupiter decametric (Io‐DAM) emissions observed by Juno/Waves, the Nançay Decameter Array, and NenuFAR. Using an up‐to‐date magnetic field model and three methods to position the active Io Flux Tube (IFT), we accurately locate the radiosources and determine their emission angle θ from the local magnetic field vector. These methods use (a) updated models of the IFT equatorial lead angle, (b) ultraviolet (UV) images of Jupiter's aurorae, and (c) multi‐point radio measurements. The kinetic energy Ee− of source electrons is then inferred from θ in the framework of the Cyclotron Maser Instability. The precise position of the active IFT achieved from methods (b and c) can be used to test the effective plasma density of the Io torus. Simultaneous radio/UV observations reveal that multiple Io‐DAM arcs are associated with multiple UV spots and provide the first direct evidence of an Io‐DAM arc associated with a trans‐hemispheric beam UV spot. Multi‐point radio observations probe the Io‐DAM sources at various altitudes, times and hemispheres. Overall, θ varies a function of frequency (altitude), by decreasing from 75°−80° to 70°−75° over 10−40 MHz with slightly larger values in the northern hemisphere, and independently varies as a function of time (or longitude of Io). Its uncertainty of a few degrees is dominated by the error on the longitude of the active IFT. The inferred values of Ee− also vary as a function of altitude and time. For the 11 investigated cases, they range from 3 to 16 keV, with a 6.6 ± 2.7 keV average.

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Section: Single‐point Radio Observations: Toward a Statistical Studycontrasting

confidence: 99%

Section: Application To Case Studies Investigated In Other Recent Art...mentioning

confidence: 99%

Section: Single‐point Radio Observations: Toward a Statistical Studymentioning

confidence: 99%

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confidence: 99%

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Determining the Beaming of Io Decametric Emissions: A Remote Diagnostic to Probe the Io‐Jupiter Interaction

et al. 2022

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“…The magnetic field magnitude computed at Jupiter's surface varies from a minimum of just under 2 Gauss to a maximum of almost 22 Gauss. Surface magnetic field strengths along the IFT footprint approach a maximum of 20 Gauss in the north (near 190° System III longitude) and 12 Gauss in the south (near 240° System III), well more than needed to explain Io-related radio observations originating from the IFT footprint (e.g., Genova & Aubier, 1985;Hess et al, 2011;Martos et al, 2020).…”

Section: Resultsmentioning

confidence: 86%

A New Model of Jupiter's Magnetic Field at the Completion of Juno's Prime Mission

et al. 2022

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A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during 32 of its first 33 polar orbits. These Prime Mission orbits sample Jupiter's magnetic field nearly uniformly in longitude (∼11° separation) as measured at equator crossing. The planetary magnetic field is represented with a degree 30 spherical harmonic and the external field is approximated near the origin with a simple external spherical harmonic of degree 1. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model (“JRM33”) of the planetary magnetic field with spherical harmonic coefficients reasonably well determined through degree and order 13. Useful information regarding the field extends through degree 18, well fit by a Lowes' spectrum with a dynamo core radius of 0.81 Rj, presumably the outer radius of the convective metallic hydrogen region. This new model provides a most detailed view of a planetary dynamo and evidence of advection of the magnetic field by deep zonal winds in the vicinity of the Great Blue Spot (GBS), an isolated and intense patch of flux near Jupiter's equator. Comparison of the JRM33 and JRM09 models suggests secular variation of the field in the vicinity of the GBS during Juno's nearly 5 years of operation in orbit about Jupiter. The observed secular variation is consistent with the penetration of zonal winds to a depth of ∼3,500 km where a flow velocity of ∼0.04 ms−1 is required to match the observations.

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Statistical study of the Jovian decametric radio emissions based on multiple-view observations from remote radio instruments

Zheng¹,

Wang²,

Li³

et al. 2023

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To better understand the physical processes associated with Jovian decametric (DAM) radio emissions, we present a statistical study of DAM emissions and inferred characteristics of DAM sources based on multiview observations from the Wind and STEREO spacecraft. Altogether, we analyze 81 isolated, strong events in radio dynamic spectra from 2008 to 2014. The apparent rotation speed of DAM events derived from multiple spacecraft observations can be used to distinguish Io-related and non-Io-related DAM emission. We find that the rotation speed of Io-DAM events is in the range of 0.15–0.6 ΩJ and that the rotation speed of non-Io DAM events is between 0.7–1.2 ΩJ. We find the occurrence probability of isolated, strong Io-DAM events to be about seven times that of isolated, strong non-Io DAM events. We locate the sources of 79 DAM events (including ten events observed by the Nançay Decameter Array) and infer their emission angles and associated electron energy. Our statistical results show that the DAM source locations (both Io and non-Io) are distributed in three preferred high-latitude regions, with two in the southern hemisphere (around 30° to 150° and around 270° to 330° in System III longitudes) and one in the northern hemisphere (around 150° to 210°), which is probably caused by the nonsymmetrical topology of Jupiter’s magnetic field. The difference between the Io-DAM source footprints and the Io auroral UV spots changes with the Io position in System III longitude, which is consistent with previous results. In addition, for the same type of DAM events (e.g., type A or C), the emission angles of non-Io DAM events are smaller than those of Io-DAM events, and all the emission angles range from 60° to 85°. Correspondingly, the energy associated with the electrons responsible for exciting the radio emissions is estimated to range between 2 and 22 keV.

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Juno Reveals New Insights Into Io‐Related Decameter Radio Emissions

Cited by 5 publications

References 51 publications

Determining the Beaming of Io Decametric Emissions: A Remote Diagnostic to Probe the Io‐Jupiter Interaction

Determining the Beaming of Io Decametric Emissions: A Remote Diagnostic to Probe the Io‐Jupiter Interaction

A New Model of Jupiter's Magnetic Field at the Completion of Juno's Prime Mission

Statistical study of the Jovian decametric radio emissions based on multiple-view observations from remote radio instruments

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