322 results found
Carbary JF, Mitchell DG, Kollmann P, et al., 2018, Energetic Electron Pitch Angle Distributions During the Cassini Final Orbits, Geophysical Research Letters, Vol: 45, Pages: 2911-2917, ISSN: 0094-8276
©2018. American Geophysical Union. All Rights Reserved. Pitch angle distributions (PADs) of very energetic electrons (110–365 keV) are examined during the ring-grazing and proximal orbits of the Cassini spacecraft, from day 320 2016 (15 November) to day 257 2017 (14 September). These repeating orbits allowed a statistical evaluation of the PADs within the magnetopause on the nightside of Saturn. Along L-shells (i.e., equatorial crossing distances of magnetic field lines) near and outside that of Titan and north of the equator, the electron fluxes were unidirectionally field-aligned going away from Saturn. Along L-shells inside Titan's and south of the equator, the electrons had bidirectional or pancake (trapping) PADs. This behavior suggests that the field lines within Titan's L-shell are generally closed, while those outside of that L-shell are generally open. This result strictly applies only to the nightside local times sampled during the final Cassini orbits, but one may infer a similar behavior at other times.
Dougherty MK, Spilker LJ, 2018, Review of Saturn's icy moons following the Cassini mission, REPORTS ON PROGRESS IN PHYSICS, Vol: 81, ISSN: 0034-4885
Davies EH, Masters A, Dougherty MK, et al., 2017, Swept Forward Magnetic Field Variability in High-Latitude Regions of Saturn's Magnetosphere, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 12328-12337, ISSN: 2169-9380
Dougherty MK, 2017, CASSINI-HUYGENS Saturn in the infrared, NATURE ASTRONOMY, Vol: 1, Pages: 579-579, ISSN: 2397-3366
Khurana KK, Fatemi S, Lindkvist J, et al., 2017, The role of plasma slowdown in the generation of Rhea's Alfven wings, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 1778-1788, ISSN: 2169-9380
Saturn's dayside aurora displays a number of morphological features poleward of the main emission region. We present an unusual morphology captured by the Hubble Space Telescope on 14 June 2014 (day 165), where for 2 h, Saturn's FUV aurora faded almost entirely, with the exception of a distinct emission spot at high latitude. The spot remained fixed in local time between 10 and 15 LT and moved poleward to a minimum colatitude of ~4°. It was bright and persistent, displaying intensities of up to 49 kR over a lifetime of 2 h. Interestingly, the spot constituted the entirety of the northern auroral emission, with no emissions present at any other local time—including Saturn's characteristic dawn arc, the complete absence of which is rarely observed. Solar wind parameters from propagation models, together with a Cassini magnetopause crossing and solar wind encounter, indicate that Saturn's magnetosphere was likely to have been embedded in a rarefaction region, resulting in an expanded magnetosphere configuration during the interval. We infer that the spot was sustained by reconnection either poleward of the cusp or at low latitudes under a strong component of interplanetary magnetic field transverse to the solar wind flow. The subsequent poleward motion could then arise from either reconfiguration of successive open field lines across the polar cap or convection of newly opened field lines. We also consider the possible modulation of the feature by planetary period rotating current systems.
Masters A, Sulaiman AH, Stawarz L, et al., 2017, An in situ Comparison of Electron Acceleration at Collisionless Shocks under Differing Upstream Magnetic Field Orientations, ASTROPHYSICAL JOURNAL, Vol: 843, ISSN: 0004-637X
Omidi N, Sulaiman AH, Kurth W, et al., 2017, A Single Deformed Bow Shock for Titan-Saturn System, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 11058-11075, ISSN: 2169-9380
During periods of high solar wind pressure, Saturn’s bow shock is pushed inside Titan’s orbitexposing the moon and its ionosphere to the solar wind. The Cassini spacecraft’s T96 encounter with Titanoccurred during such a period and showed evidence for shocks associated with Saturn and Titan. It alsorevealed the presence of two foreshocks: one prior to the closest approach (foreshock 1) and one after(foreshock 2). Using electromagnetic hybrid (kinetic ions and fluid electrons) simulations and Cassiniobservations,we showthat the origin of foreshock 1 is tied to the formation of a single deformed bow shock forthe Titan-Saturn system. We also report the observations of a structure in foreshock 1 with properties consistentwith those of spontaneous hot flow anomalies formed in the simulations and previously observed at Earth,Venus, and Mars. The results of hybrid simulations also show the generation of oblique fast magnetosonicwaves upstream of the outbound Titan bow shock in agreement with the observations of large-amplitudemagnetosonic pulsations in foreshock 2. We also discuss the implications of a single deformed bow shock fornew particle acceleration mechanisms and also Saturn’s magnetopause and magnetosphere.
Sergis N, Jackman CM, Thomsen MF, et al., 2017, Radial and local time structure of the Saturnian ring current, revealed by Cassini, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 1803-1815, ISSN: 2169-9380
Sorba AM, Achilleos NA, Guio P, et al., 2017, Modeling the compressibility of Saturn's magnetosphere in response to internal and external influences, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 122, Pages: 1572-1589, ISSN: 2169-9380
Witasse O, Sanchez-Cano B, Mays ML, et al., 2017, Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU, Journal of Geophysical Research: Space Physics, Vol: 122, Pages: 7865-7890, ISSN: 2169-9380
We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110–111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116°, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
Yao ZH, Coates AJ, Ray LC, et al., 2017, Corotating Magnetic Reconnection Site in Saturn's Magnetosphere, ASTROPHYSICAL JOURNAL LETTERS, Vol: 846, ISSN: 2041-8205
Using measurements from theCassinispacecraft in Saturn’s magnetosphere, we propose a 3D physical picture of acorotating reconnection site, which can only be driven by an internally generated source. Our results demonstratethat the corotating magnetic reconnection can drive an expansion of the current sheet in Saturn’s magnetosphereand, consequently, can produce Fermi acceleration of electrons. This reconnection site lasted for longer than one ofSaturn’s rotation period. The long-lasting and corotating natures of the magnetic reconnection site at Saturnsuggest fundamentally different roles of magnetic reconnection in driving magnetospheric dynamics(e.g., theauroral precipitation)from the Earth. Our corotating reconnection picture could also potentially shed light on thefast rotating magnetized plasma environments in the solar system and beyond.
Yao ZH, Radioti A, Rae IJ, et al., 2017, Mechanisms of Saturn's Near-Noon Transient Aurora: In Situ Evidence From Cassini Measurements, GEOPHYSICAL RESEARCH LETTERS, Vol: 44, Pages: 11217-11228, ISSN: 0094-8276
Although auroral emissions at giant planets have been observed for decades, the physical mechanisms of aurorae at giant planets remain unclear. One key reason is the lack of simultaneous measurements in the magnetosphere while remote sensing of the aurora. We report a dynamic auroral event identified with the Cassini Ultraviolet Imaging Spectrograph (UVIS) at Saturn on 13 July 2008 with coordinated measurements of the magnetic field and plasma in the magnetosphere. The auroral intensification was transient, only lasting for ∼30 min. The magnetic field and plasma are perturbed during the auroral intensification period. We suggest that this intensification was caused by wave mode conversion generated field-aligned currents, and we propose two potential mechanisms for the generation of this plasma wave and the transient auroral intensification. A survey of the Cassini UVIS database reveals that this type of transient auroral intensification is very common (10/11 time sequences, and ∼10% of the total images).
Arridge CS, Eastwood JP, Jackman CM, et al., 2016, Cassini in situ observations of long-duration magnetic reconnection in Saturn's magnetotail, NATURE PHYSICS, Vol: 12, Pages: 268-271, ISSN: 1745-2473
Arridge CS, Jasinski JM, Achilleos N, et al., 2016, Cassini observations of Saturn's southern polar cusp, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 3006-3030, ISSN: 2169-9380
Badman SV, Provan G, Bunce EJ, et al., 2016, Saturn's auroral morphology and field-aligned currents during a solar wind compression, ICARUS, Vol: 263, Pages: 83-93, ISSN: 0019-1035
Felici M, Arridge CS, Coates AJ, et al., 2016, Cassini observations of ionospheric plasma in Saturn's magnetotail lobes, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 338-357, ISSN: 2169-9380
Hunt GJ, Cowley SWH, Provan G, et al., 2016, Field-aligned currents in Saturn's magnetosphere: Local time dependence of southern summer currents in the dawn sector between midnight and noon, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 7785-7804, ISSN: 2169-9380
Kurth WS, Hospodarsky GB, Gurnett DA, et al., 2016, Saturn kilometric radiation intensities during the Saturn auroral campaign of 2013, ICARUS, Vol: 263, Pages: 2-9, ISSN: 0019-1035
Lai HR, Russell CT, Jia YD, et al., 2016, Transport of magnetic flux and mass in Saturn's inner magnetosphere, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 3050-3057, ISSN: 2169-9380
Provan G, Cowley SWH, Lamy L, et al., 2016, Planetary period oscillations in Saturn's magnetosphere: Coalescence and reversal of northern and southern periods in late northern spring, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 9829-9862, ISSN: 2169-9380
Regoli LH, Roussos E, Feyerabend M, et al., 2016, Access of energetic particles to Titan's exobase: A study of Cassini's T9 flyby, PLANETARY AND SPACE SCIENCE, Vol: 130, Pages: 40-53, ISSN: 0032-0633
Roussos E, Krupp N, Mitchell DG, et al., 2016, Quasi-periodic injections of relativistic electrons in Saturn's outer magnetosphere, ICARUS, Vol: 263, Pages: 101-116, ISSN: 0019-1035
Sulaiman AH, Masters A, Dougherty MK, 2016, Characterization of Saturn's bow shock: Magnetic field observations of quasi-perpendicular shocks, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 4425-4434, ISSN: 2169-9380
Bertucci C, Hamilton DC, Kurth WS, et al., 2015, Titan's interaction with the supersonic solar wind, GEOPHYSICAL RESEARCH LETTERS, Vol: 42, Pages: 193-200, ISSN: 0094-8276
Engelhardt IAD, Wahlund J-E, Andrews DJ, et al., 2015, Plasma regions, charged dust and field-aligned currents near Enceladus, PLANETARY AND SPACE SCIENCE, Vol: 117, Pages: 453-469, ISSN: 0032-0633
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