Understanding the Origin of Jupiter's Diffuse Aurora Using Juno's First Perijove Observations

Li, W.; Thorne, R. M.; Zhang, X.-J.; Gladstone, G. Randall; Hue, V.; Valek, P. W.; Allegrini, F.; Mauk, B. H.; Clark, G.; Kurth, W. S.; Hospodarsky, G. B.; Connerney, J. E. P.; Bolton, S. J.

doi:10.1002/2017gl075545

Cited by 21 publications

(31 citation statements)

References 45 publications

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“…Inversely, the main emission peak at 1.33 × 10 4 km shows the lowest IR/UV ratio and the highest color ratio (8.5) along the cut. The infrared emission is significantly enhanced in this region relative to the FUV, in agreement with the drop in mean electron energy measured in situ by JADE and JEDI during the later Juno crossing of this zone ( Li et al, 2017 ;Fig. 2 ).…”

Section: Comparative Intensity Distributionsupporting

confidence: 88%

“…Globally, these results show a trend for high FUV/IR ratio associated with areas of relatively high color ratio. Li et al (2017) analyzed the morphology of the UV diffuse aurora in parallel with the in situ characteristics of the electron precipitation in the diffuse region measured a couple of hours later near λ III = 120 °-150 °They provided evidence that the loss cone was nearly full over energies 0.1-700 keV. Pitch angle scattering into the loss cone is thought to produce diffuse auroral emissions ( Coroniti et al, 1980 ;Bhattracharya et al, 2001;Radioti et al, 2009 ).…”

Section: Fig 2 Same Asmentioning

confidence: 99%

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Concurrent ultraviolet and infrared observations of the north Jovian aurora during Juno's first perijove

Gérard

Mura

Bonfond

et al. 2018

Icarus

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The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) observed the north polar aurora before the first perijove of the Juno orbit (PJ1) on 27 August 2016. The UVS bandpass corresponds to the H 2 Lyman and Werner bands that are directly excited by collisions of auroral electrons with molecular hydrogen. The spectral window of the JIRAM L-band imager includes some of the brightest H + 3 thermal features between 3.3 and 3.6 μm. A series of spatial scans obtained with JIRAM every 30 s is used to build up five quasi-global images, each covering ∼12 min. of observations. JIRAM's best spatial resolution was on the order of 50 km/pixel during this time frame, while UVS has a resolution of about 750 km. Most of the observed large-scale auroral features are similar in the two spectral regions, but important differences are also observed in their morphology and relative intensity. Only a part of the UV-IR differences stems from the higher spatial resolution of JIRAM, as some of them are still present following smoothing of the JIRAM images at the UVS resolution. For example, the JIRAM images show persistent narrow arc structures in the 100 °-180 °S III longitude sector at dusk not resolved in the ultraviolet, but consistent with the structure of in situ electron precipitation measured two hours later. The comparison between the H 2 intensity and the H + 3 radiance measured along two radial cuts from the center of the main emission illustrates the complex relation between the electron energy input, their characteristic energy and the H + 3 emission. Low values of the H + 3 intensity relative to the H 2 brightness are observed in regions of high FUV color ratio corresponding to harder electron precipitation. The rapid loss of H + 3 ions reacting with methane near and below the homopause appears to play a significant role in the control of the relative brightness of the two emissions. Cooling of the auroral thermosphere by H + 3 radiation is spatially variable relative to the direct particle heating resulting from the precipitated electron flux.

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Section: Comparative Intensity Distributionsupporting

confidence: 88%

Section: Fig 2 Same Asmentioning

confidence: 99%

Concurrent ultraviolet and infrared observations of the north Jovian aurora during Juno's first perijove

Gérard

Mura

Bonfond

et al. 2018

Icarus

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“…Higher characteristic energies in the polar region and sometimes at the low latitude end of the intervals correspond to reddish colors, whereas the lower energies correspond to the white. The lower characteristic energy region for the downward electrons also corresponds to outer emissions (e.g., Dumont et al, 2014; Radioti et al, 2009), generally associated with pitch angle diffusion in the loss cone (Li et al, 2017).…”

Section: Resultsmentioning

confidence: 99%

Energy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission

et al. 2020

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Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3-to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (<10 keV). Its polarward edge corresponds to the equatorward edge of the main oval, which is mapped at M shells of~51. A refined current sheet model will likely bring this boundary closer to the expected 20-30 R J . Outside that region, the >100-keV electrons contribute to most (>~70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

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“…Recently published results focusing on the particle observations have shown the presence of both broadband and peaked electron energy distributions in both the downward (Allegrini et al, ; Mauk et al, , , ) and upward (Clark, Mauk, Haggerty, et al, ; Ebert et al, ) loss cones. The auroral ion observations revealed the presence of energetic ion conics (Clark, Mauk, Haggerty, et al, ), parallel potential drops (Clark, Mauk, Haggerty, et al, ; Haggerty et al, ; Mauk et al, , ), and stochastic processes likely associated with wave‐particle interactions (Elliott et al, ; Li et al, ; Louarn et al, Ma et al, ; Mauk et al, ). Perhaps one of the more surprising discoveries is the role that broadband acceleration plays in the generation of Jupiter's powerful aurora.…”

Section: Introductionmentioning

confidence: 99%

Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

et al. 2018

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The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope, and also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure—leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno/Jupiter Energetic particle Detector Instrument (JEDI), an energetic particle instrument, we present these relationships for the 30‐keV to 1‐MeV electron population. Observations presented here show that the electron energy flux in the loss cone is a nonlinear function of the characteristic or mean electron energy and supports both the predictions from Knight (1973, https://doi.org/10.1016/0032-0633(73)90093-7) and magnetohydrodynamic turbulence acceleration theories (e.g., Saur et al., 2003, https://doi.org/10.1029/2002GL015761). Finally, we compare the in situ analyses of Juno with remote Hisaki observations and use them to help constrain Jupiter's atmospheric profile. We find a possible solution that provides the best agreement between these data sets is an atmospheric profile that more efficiently transports the hydrocarbons to higher altitudes. If this is correct, it supports the previously published idea (e.g., Parkinson et al., 2006, https://doi.org/10.1029/2005JE002539) that precipitating electrons increase the hydrocarbon eddy diffusion coefficients in the auroral regions.

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Understanding the Origin of Jupiter's Diffuse Aurora Using Juno's First Perijove Observations

Cited by 21 publications

References 45 publications

Concurrent ultraviolet and infrared observations of the north Jovian aurora during Juno's first perijove

Concurrent ultraviolet and infrared observations of the north Jovian aurora during Juno's first perijove

Energy Flux and Characteristic Energy of Electrons Over Jupiter's Main Auroral Emission

Precipitating Electron Energy Flux and Characteristic Energies in Jupiter's Main Auroral Region as Measured by Juno/JEDI

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