Mapping H 3 + Temperatures in Jupiter's Northern Auroral Ionosphere Using VLT‐CRIRES

Geophysical Research Letters

et al. 2019

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We present a study of Saturn's normalH3+ northern auroral emission using data from 19 May 2013 from the Very Large Telescope's long‐slit spectrometer Cryogenic Infrared Echelle Spectrograph (VLT‐CRIRES). Adaptive optics, combined with the spectral resolution of VLT‐CRIRES ( λnormalΔλ∼100,000), offers unprecedented spectrally resolved views of Saturn's infrared aurora. Discrete normalH3+ emission lines—used to derive dawn‐to‐dusk profiles of auroral intensity, ion line‐of‐sight velocity, and thermospheric temperature—reveal a dawn‐enhanced aurora with an average temperature of 361 (±48) K and a localized dark region in the emission co‐located with a noon‐to‐midnight (and vice versa) flow in the ion velocity on the scale of ∼1 km/s, resembling an ionospheric polar vortex. A temperature hotspot of 379 (±66) K may be driving an emission region, corresponding to a location where normalH3+ is failing to cool the thermosphere. Results presented here have implications for current understanding on the complex nature of Saturn's thermosphere‐ionosphere‐magnetosphere interaction.

Section: Observations and Data Analysismentioning

confidence: 99%

Exploring Key Characteristics in Saturn's Infrared Auroral Emissions Using VLT‐CRIRES: Intensities, Ion Line‐of‐Sight Velocities, and Rotational Temperatures

Chowdhury

Geophysical Research Letters

et al. 2019

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“…By measuring the normalH3+ emission brightness from the Q (1,0 − ) and R (2,2 − ) lines, it is possible to calculate the normalH3+ temperature, column density and total emission in the same way as has been used previously at both Jupiter and Saturn (e.g. [44,47,58]). Ab initio calculations of the theoretical emission per molecule of normalH3+ provide a theoretical brightness for each line at a given temperature [59].…”

Section: Datamentioning

confidence: 99%

“…Our understanding is limited by our ability to spatially resolve emission from the auroral region, making it difficult to measure the ion currents that flow through the ionosphere or the structure of the underlying thermospheric temperatures that are either driven by these aurora, or potentially drive them. In order to better measure these values, it is essential to increase our measured signal to improve the observed signal-to-noise on the planet, as well as bettering our positioning and observing the aurora in two dimensions, so we can map out the normalH3+ accurately across the entire auroral region, a strategy that has greatly improved our understanding of Jupiter's ionosphere [46,47].…”

Section: Introductionmentioning

confidence: 99%

Local-time averaged maps of H ₃ ⁺ emission, temperature and ion winds

Baines

Phil. Trans. R. Soc. A.

et al. 2019

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We present Keck-NIRSPEC observations of Saturn's H 3 + aurora taken over a period of a month, in support of the Cassini mission's ‘Grand Finale’. These observations produce two-dimensional maps of Saturn's H 3 + temperature and ion winds for the first time. These maps show surprising complexity, with different morphologies seen in each night. The H 3 + ion winds reveal multiple arcs of 0.5–1 km s −1 ion flows inside the main auroral emission. Although these arcs of flow occur in different locations each night, they show intricate structures, including mirrored flows on the dawn and dusk of the planet. These flows do not match with the predicted flows from models of either axisymmetric currents driven by the Solar Wind or outer magnetosphere, or the planetary periodic currents associated with Saturn's variable rotation rate. The average of the ion wind flows across all the nights reveals a single narrow and focused approximately 0.3 km s −1 flow on the dawn side and broader and more extensive 1–2 km s −1 sub-corotation, spilt into multiple arcs, on the dusk side. The temperature maps reveal sharp gradients in ionospheric temperatures, varying between 300 and 600 K across the auroral region. These temperature changes are localized, resulting in hot and cold spots across the auroral region. These appear to be somewhat stable over several nights, but change significantly over longer periods. The position of these temperature extremes is not well organized by the planetary period and there is no evidence for a thermospheric driver of the planetary period current system. Since no past magnetospheric or thermospheric models explain the rich complexity observed here, these measurements represent a fantastic new resource, revealing the complexity of the interaction between Saturn's thermosphere, ionosphere and magnetosphere. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

“…In order to convert these to represent the intensity observed along the ‘surface’ normal, a line-of-sight correction is applied (e.g. [11]).…”

Section: Resultsmentioning

confidence: 99%

The H ₃ ⁺ ionosphere of Uranus: decades-long cooling and local-time morphology

Fletcher

Phil. Trans. R. Soc. A.

et al. 2019

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The upper atmosphere of Uranus has been observed to be slowly cooling between 1993 and 2011. New analysis of near-infrared observations of emission from H 3 + obtained between 2012 and 2018 reveals that this cooling trend has continued, showing that the upper atmosphere has cooled for 27 years, longer than the length of a nominal season of 21 years. The new observations have offered greater spatial resolution and higher sensitivity than previous ones, enabling the characterization of the H 3 + intensity as a function of local time. These profiles peak between 13 and 15 h local time, later than models suggest. The NASA Infrared Telescope Facility iSHELL instrument also provides the detection of a bright H 3 + signal on 16 October 2016, rotating into view from the dawn sector. This feature is consistent with an auroral signal, but is the only of its kind present in this comprehensive dataset. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.