The brightness ratio of H Lyman‐<i>α</i>/H<sub>2</sub> bands in FUV auroral emissions: A diagnosis for the energy of precipitating electrons and associated magnetospheric acceleration processes applied to Saturn

Tao, Chihiro; Lamy, Laurent; Prangé, Renée

doi:10.1002/2014gl061329

Cited by 13 publications

(15 citation statements)

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“…By considering another wave amplitude E wave = 0.15 mVm −1 the intensities and energy flux are reduced to less than 50% for shell L = 7 and about 50% at shell 5.35 to the values calculated by using E wave = 0.30 mVm −1 . Precipitation of electrons in an H 2 atmosphere has also been studied in other works (e.g., Gerard & Singh, ; Tao et al, ). Using a Maxwellian electron distribution with characteristic energy 2 keV and energy flux 1 erg · cm −2 · s −1 , Gerard and Singh () obtain intensities 5.4 and 5.2 kR for H 2 Lyman and Werner bands, respectively.…”

Section: Resultsmentioning

confidence: 82%

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The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

2018

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In the present paper we have modeled diffuse auroral emissions, which have been observed at lower latitudes as compared to the main auroral arc at Saturn. It is generally accepted that these emissions are generated by precipitation of hot population of magnetospheric electrons on the closed field lines. We have considered the pitch angle diffusion by electrostatic electron cyclotron harmonic waves as the mechanism to diffuse trapped electrons into the atmospheric loss cone. Electrons are thereby precipitated into the atmosphere and excite the neutral atmospheric constituents producing auroral emissions. Calculation of ultraviolet emission intensities has been performed at two L‐shells 5.35 and 7.0. Observed hot electron distribution functions and observed electrostatic electron cyclotron harmonic wave characteristics have been used in the study. Intensities of Lyman‐alpha emission from excitation of atomic H and Lyman‐alpha produced from dissociative excitation of H2 have been calculated, obtaining the values 20.1 R (1.8 R) and 1.6 kR (0.29 kR), respectively, for both L‐shells 7.0 (5.35).Further, intensities of Lyman and Werner bands of H2 are also calculated. These have the values 7.50 kR (1.43 kR) and 7.52 kR (1.49 kR), respectively, for L‐shells 7.0 (5.35). It is observed that the volume excitation rates of these four excitations peak at an altitude of about 2,000 km. From the range‐energy relation in H2 gas it is estimated that the electrons producing these excitations should have energies less than about 250 eV.

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Section: Resultsmentioning

confidence: 82%

“…The ratio of brightness of H Ly‐α to that of H 2 band brightness (H/H 2 brightness ratio) obtained in the present study is ~0.11. Tao et al () report for the ratio of the energy deposited into the H Ly‐α line and into the H 2 Lyman and Werner bands, a value ~0.27. The ratio decreases with increasing brightness of H 2 bands.…”

Section: Resultsmentioning

confidence: 99%

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

2018

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“…The field-aligned currents that stimulate the intensification of the SKR (and cause the LFE) are associated with the precipitation of ∼1-to 20-keV electrons into Saturn's atmosphere, producing UV (ultraviolet) aurora (Gustin et al, 2017;Lamy et al, 2010;Mutel et al, 2010;Tao et al, 2014). The link between magnetotail reconnection, LFEs, and auroral forms at Saturn was first postulated by Cowley et al (2005).…”

Section: Case Study 2: Postmidnight Tailward Motionmentioning

confidence: 99%

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

et al. 2018

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Reconnection is a fundamentally important process in planetary magnetospheres, with both local and global effects. At Saturn, observations of the magnetotail reconnection site (or x‐line) are rare, with only one in situ encounter reported to date. In this work, an extensive database of plasmoids and dipolarizations (Smith et al., 2016, https://doi.org/10.1002/2015JA022005) was investigated from a multi‐instrument perspective in order to probe the location and variability of the magnetotail x‐line. Several clear intervals were identified in which the x‐line location could be indirectly inferred to move on relatively short timescales. Two case studies are presented, the first of which concerns short‐lived flows, suggesting the reconnection sites can be either short‐lived (∼10 minutes) or extremely azimuthally limited (∼3RS/0.4 hr of local time). The second interval concerns the tailward motion of the reconnection site (or sites), inferred from the increasing electron temperature (and diminishing electron density) associated with the flows. This tailward motion occurs over ∼2.5 hr (approximately a quarter of a planetary rotation). The composition of the suprathermal plasma suggests that this could be an example of the gradual depletion of mass‐loaded flux tubes (that must occur prior to lobe reconnection). These case studies are consistent with previous statistical work that suggested that the site of reconnection in the Kronian magnetotail can be highly dynamic.

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“…The high‐latitude emissions sometimes show electron energies and energy fluxes similar to those of the main oval emissions; however, high electron energies (large CR) with low fluxes are also present [ Gustin et al ., ]. The CR related to the brightness of H Lyman α and H 2 has also been applied [e.g., Harris et al ., ], which is suggested to be sensitive to lower energy electrons because the CR refers to hydrogen atoms at a higher altitude [ Tao et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

et al. 2016

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Temporal variation of Jupiter's northern aurora is detected using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on board JAXA's Earth‐orbiting planetary space telescope Hisaki. The wavelength coverage of EXCEED includes the H2 Lyman and Werner bands at 80–148 nm from the entire northern polar region. The prominent periodic modulation of the observed emission corresponds to the rotation of Jupiter's main auroral oval through the aperture, with additional superposed −50%–100% temporal variations. The hydrocarbon color ratio (CR) adopted for the wavelength range of EXCEED is defined as the ratio of the emission intensity in the long wavelength range of 138.5–144.8 nm to that in the short wavelength range of 126.3–130 nm. This CR varies with the planetary rotation phase. Short‐ (within one planetary rotation) and long‐term (> one planetary rotation) enhancements of the auroral power are observed in both wavelength ranges and result in a small CR variation. The occurrence timing of the auroral power enhancement does not clearly depend on the central meridian longitude. Despite the limitations of the wavelength coverage and the large field of view of the observation, the auroral spectra and CR‐brightness distribution measured using EXCEED are consistent with other observations.

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The brightness ratio of H Lyman‐α/H₂ bands in FUV auroral emissions: A diagnosis for the energy of precipitating electrons and associated magnetospheric acceleration processes applied to Saturn

Cited by 13 publications

References 34 publications

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

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The brightness ratio of H Lyman‐α/H2 bands in FUV auroral emissions: A diagnosis for the energy of precipitating electrons and associated magnetospheric acceleration processes applied to Saturn

Cited by 13 publications

References 34 publications

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

Multi‐instrument Investigation of the Location of Saturn's Magnetotail X‐Line

Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS

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The brightness ratio of H Lyman‐α/H₂ bands in FUV auroral emissions: A diagnosis for the energy of precipitating electrons and associated magnetospheric acceleration processes applied to Saturn