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  • 1
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    Global response of the upper thermospheric winds to large ion drifts in the jovian ovals (2016)
    Wiley
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    Publication Date: 2016-03-25
    Description: We use our fully coupled 3-D Jupiter Thermosphere General Circulation Model (JTGCM) to quantify processes which are responsible for generating neutral winds in Jupiter's oval thermosphere from 20 µbar to 10 -4 nbar self-consistently with the thermal structure and composition. The heat sources in the JTGCM that drive the global circulation of neutral flow are substantial Joule heating produced in the Jovian ovals by imposing high speed anticorotational ion drifts (~3.5 kms -1 ) and charged particle heating from auroral processes responsible for bright oval emissions. We find that the zonal flow of neutral winds in the auroral ovals of both hemispheres is primarily driven by competition between accelerations resulting from Coriolis forcing and ion drag processes near the ionospheric peak. However, above the ionospheric peak (〈0.01 µbar), the acceleration of neutral flow due to pressure gradients is found to be the most effective parameter impacting zonal winds, competing mainly with acceleration due to advection with minor contributions from curvature and Coriolis forces in the southern oval, while in the northern oval it competes alone with considerable Coriolis forcing. The meridional flow of neutral winds in both ovals in the JTGCM is determined by competition between meridional accelerations due to Coriolis forcing and pressure gradients. We find that meridional flow in the lower thermosphere, near the peak of the auroral ionosphere, is poleward, with peak wind speeds of ~0.6 kms -1 and ~0.1 kms -1 in the southern and northern oval, respectively. The corresponding subsiding flow of neutral motion is ~5 ms -1 in the southern oval, while this flow is rising in the northern oval with reduced speed of ~2 ms -1 . We also find that the strength of meridional flow in both auroral ovals is gradually weakened and turned equatorward near 0.08 µbar with wind speeds up to ~250 ms -1 (southern oval) and ~75 ms -1 (northern oval). The corresponding neutral motion in this region is upward, with wind speeds up to 4 ms -1 in both ovals.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Search for Saturn's X-ray aurorae at the arrival of a solar wind shock (2013)
    Wiley
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    Publication Date: 2013-01-17
    Description: [1]  After a decade of observations, evidence for X-ray auroral emission from Saturn has yet to be found. By analogy with processes known to take place on Jupiter, Saturnian X-ray aurorae may be expected to be powered by charge exchange (CX) between energetic ions and the planet's atmospheric neutrals; if the ions are of solar origin, the emission should be brightest during episodes of enhanced solar wind (SW). We have explored this possibility by propagating SW parameters measured near the Earth to Saturn, and triggering X-ray observations at the time SW enhancements were expected to reach the planet. This was done in April–May 2011 with the Chandra X-ray Observatory, and we report on two observations carried out at the time when a significant SW disturbance reached Saturn, as indicated by Cassini magnetic field, plasma and radio measurements: variability is observed between the two Chandra datasets, but we do not find evidence for X-ray brightening in the auroral regions. The variability can be explained by scattering of solar X-rays in Saturn's atmosphere during an episode of solar X-ray flaring. We conclude that the strength of any CX auroral X-ray emission on Saturn was below Chandra's detectability threshold. By-products of this investigation are stringent upper limits on the X-ray emission of Titan and Enceladus. The Cassini measurements concurrent with the Chandra observations confirm and pinpoint temporally the arrival of the SW enhancement at Saturn. SW propagation predictions are a useful tool for investigating and interpreting the effects of SW interactions with planetary environments.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Titan airglow during eclipse (2012)
    Wiley
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    Publication Date: 2012-09-28
    Description: Solar XUV photons can provide enough energy to account for the observed nitrogen UV dayglow emissions above 800 km, but a small or sporadic contribution from energetic particles cannot be ruled out. Furthermore, ion production at altitudes deeper than 800 km as inferred from radio occultation cannot be produced by solar XUV stimulation and implies energy deposition from protons and oxygen ions. Here we examine UV spectra and visible-wavelength images of Titan in Saturn's shadow, when XUV stimulation is absent. UV emissions are observed in one of the three sets of spectra, and the intensity of these emissions is about a factor of 10 less than the peak intensity reported on the dayside. We observe visible-wavelength emissions for the first time. No horizontally resolved auroral structures are seen in the visible images. At visible wavelengths Titan has a global emission at the haze-top level that is not understood, although cosmic ray ionization and chemiluminescence are candidates needing further investigation.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Lunar atmospheric helium detections by the LAMP UV spectrograph on the Lunar Reconnaissance Orbiter (2012)
    Wiley
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    Publication Date: 2012-06-27
    Description: The LAMP far ultraviolet spectrograph aboard the NASA Lunar Reconnaissance Orbiter has been used in 2011 to search for helium, the lightest noble gas in the tenuous lunar atmosphere. Based on that search, we report here the first detection of lunar atmospheric He by remote sensing, and point to future observations that can address questions about its source; we also discuss a search for lunar atmospheric argon.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Juno‐UVS observation of the Io footprint during solar eclipse (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The two main UV‐signatures resulting from the Io‐magnetosphere interaction are the local auroras on Io's atmosphere, and the Io footprints on Jupiter. We study here how Io's daily eclipses affect the footprint. Previous observations showed that its atmosphere collapses in eclipse. While remote observers can observe Io's local auroras briefly when Io disappears behind Jupiter, Juno is able to follow the Io footprint in the unlit hemisphere. Theoretical models of the variability of the energy flux fed into the Alfvén wings, ultimately powering the footprints, are not sufficiently constrained by observations. For the first time, we use observations of Io's footprint from the Ultraviolet Spectrograph on Juno recorded as Io went into eclipse. We benchmark the trend of the footprint brightness using observations by UVS taken over Io's complete orbit and find that the footprint emitted power variation with Jupiter's rotation shows fairly consistent trends with previous observations. Two exploitable datasets provided measurements when Io was simultaneously in eclipse. No statistically significant changes were recorded as Io left and moved into eclipse, respectively, suggesting either that (i) Io's atmospheric densities within and outside eclipse are large enough to produce a saturated plasma interaction, i.e., in the saturated state, changes in Io's atmospheric properties to first order do not control the total Alfvénic energy flux, (ii) the atmospheric collapse during the Juno observations was less than previously observed, or (iii) additional processes of the Alfvén wings in addition to the Poynting flux generated at Io control the footprint luminosity.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    A Rapid Decrease of the Hydrogen Corona of Mars (2014)
    Wiley
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    Publication Date: 2014-11-08
    Description: Mars is believed to have lost much of its surface water 3.5 billion years ago, but the amounts that escaped into space and remain frozen in the crust today are not well known. Hydrogen atoms in the extended martian atmosphere, some of which escape the planet's gravity, can be imaged through scattered solar UV radiation. Hubble Space Telescope (HST) images of the ultraviolet H Ly α emission now indicate that the coronal H density steadily decreased by a factor of roughly 40 % over 4 weeks, a far greater variation than had been expected. The leading candidate cause is a decrease in the source rate of water molecules from the lower atmosphere, consistent with seasonal changes and a recent global dust storm. This implies that the rate of escape of martian hydrogen (and thereby water) into space is strongly dependent on the lower atmospheric water content and distribution.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 7
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    Detection of atomic deuterium in the upper atmosphere of Mars (1998)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1998-06-11
    Description: High-resolution spectroscopy of Mars' atmosphere with the Hubble Space Telescope revealed the deuterium Lyman alpha line at an intensity of 23 +/- 6 rayleighs. This measured intensity corresponds to HD/H2 = 1.5 +/- 0.6 x 10(-4), which is smaller by a factor of 11 than HDO/H2O. This indicates that fractionation of HD/H2 relative to that of HDO/H2O is not kinetically controlled by the rates of formation and destruction of H2 and HD but is thermodynamically controlled by the isotope exchange HD + H2O left and right arrow HDO + H2. Molecular hydrogen is strongly depleted in deuterium relative to water on Mars because of the very long lifetime of H2 (1200 years). The derived isotope fractionation corresponds to an estimate of a planetwide reservoir of water ice about 5 meters thick that is exchangeable with the atmosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Krasnopolsky, V A -- Mumma, M J -- Gladstone, G R -- New York, N.Y. -- Science. 1998 Jun 5;280(5369):1576-80.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, Catholic University of America, Washington, DC 20064, USA. VKras@lepvx3.gsfc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9616115" target="_blank"〉PubMed〈/a〉
    Keywords: Atmosphere ; Deuterium/*analysis ; *Extraterrestrial Environment ; Hydrogen/*analysis ; Ice ; *Mars ; Temperature ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    Polar lightning and decadal-scale cloud variability on Jupiter (2007)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2007-10-13
    Description: Although lightning has been seen on other planets, including Jupiter, polar lightning has been known only on Earth. Optical observations from the New Horizons spacecraft have identified lightning at high latitudes above Jupiter up to 80 degrees N and 74 degrees S. Lightning rates and optical powers were similar at each pole, and the mean optical flux is comparable to that at nonpolar latitudes, which is consistent with the notion that internal heat is the main driver of convection. Both near-infrared and ground-based 5-micrometer thermal imagery reveal that cloud cover has thinned substantially since the 2000 Cassini flyby, particularly in the turbulent wake of the Great Red Spot and in the southern half of the equatorial region, demonstrating that vertical dynamical processes are time-varying on seasonal scales at mid- and low latitudes on Jupiter.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Baines, Kevin H -- Simon-Miller, Amy A -- Orton, Glenn S -- Weaver, Harold A -- Lunsford, Allen -- Momary, Thomas W -- Spencer, John -- Cheng, Andrew F -- Reuter, Dennis C -- Jennings, Donald E -- Gladstone, G R -- Moore, Jeffrey -- Stern, S Alan -- Young, Leslie A -- Throop, Henry -- Yanamandra-Fisher, Padma -- Fisher, Brendan M -- Hora, Joseph -- Ressler, Michael E -- New York, N.Y. -- Science. 2007 Oct 12;318(5848):226-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17932285" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Io's atmospheric response to eclipse: UV aurorae observations (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-10-13
    Description: The New Horizons (NH) spacecraft observed Io's aurora in eclipse on four occasions during spring 2007. NH Alice ultraviolet spectroscopy and concurrent Hubble Space Telescope ultraviolet imaging in eclipse investigate the relative contribution of volcanoes to Io's atmosphere and its interaction with Jupiter's magnetosphere. Auroral brightness and morphology variations after eclipse ingress and egress reveal changes in the relative contribution of sublimation and volcanic sources to the atmosphere. Brightnesses viewed at different geometries are best explained by a dramatic difference between the dayside and nightside atmospheric density. Far-ultraviolet aurora morphology reveals the influence of plumes on Io's electrodynamic interaction with Jupiter's magnetosphere. Comparisons to detailed simulations of Io's aurora indicate that volcanoes supply 1 to 3% of the dayside atmosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Retherford, K D -- Spencer, J R -- Stern, S A -- Saur, J -- Strobel, D F -- Steffl, A J -- Gladstone, G R -- Weaver, H A -- Cheng, A F -- Parker, J Wm -- Slater, D C -- Versteeg, M H -- Davis, M W -- Bagenal, F -- Throop, H B -- Lopes, R M C -- Reuter, D C -- Lunsford, A -- Conard, S J -- Young, L A -- Moore, J M -- New York, N.Y. -- Science. 2007 Oct 12;318(5848):237-40.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Southwest Research Institute, San Antonio, TX 78228, USA. KRetherford@swri.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17932289" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Jupiter's nightside airglow and aurora (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-10-13
    Description: Observations of Jupiter's nightside airglow (nightglow) and aurora obtained during the flyby of the New Horizons spacecraft show an unexpected lack of ultraviolet nightglow emissions, in contrast to the case during the Voyager flybys in 1979. The flux and average energy of precipitating electrons generally decrease with increasing local time across the nightside, consistent with a possible source region along the dusk flank of Jupiter's magnetosphere. Visible emissions associated with the interaction of Jupiter and its satellite Io extend to a surprisingly high altitude, indicating localized low-energy electron precipitation. These results indicate that the interaction between Jupiter's upper atmosphere and near-space environment is variable and poorly understood; extensive observations of the day side are no guide to what goes on at night.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gladstone, G Randall -- Stern, S Alan -- Slater, David C -- Versteeg, Maarten -- Davis, Michael W -- Retherford, Kurt D -- Young, Leslie A -- Steffl, Andrew J -- Throop, Henry -- Parker, Joel Wm -- Weaver, Harold A -- Cheng, Andrew F -- Orton, Glenn S -- Clarke, John T -- Nichols, Jonathan D -- New York, N.Y. -- Science. 2007 Oct 12;318(5848):229-31.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Southwest Research Institute, San Antonio, TX 78238, USA. rgladstone@swri.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17932286" target="_blank"〉PubMed〈/a〉
    Keywords: Extraterrestrial Environment ; Hydrocarbons ; Hydrogen ; *Jupiter ; Magnetics ; Spacecraft
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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