Publications
403 results found
Pilkington NM, Achilleos N, Arridge CS, et al., 2015, Internally driven large-scale changes in the size of Saturn's magnetosphere, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 7289-7306, ISSN: 2169-9402
Saturn's magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system's dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma-loaded” or “plasma-depleted” states, defined in terms of the internal suprathermal plasma pressure.
Pilkington NM, Achilleos N, Arridge CS, et al., 2015, Asymmetries observed in Saturn's magnetopause geometry, Geophysical Research Letters, Vol: 42, Pages: 6890-6898, ISSN: 1944-8007
For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn-dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn-dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the “intrinsic” polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north-south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10–17°).
Yates JN, Southwood DJ, Dougherty MK, 2015, Reply to the comment by Cowley et al. on “Magneticphase structure of Saturn’s 10.7h oscillations”, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 5691-5693, ISSN: 2169-9402
Jackman CM, Thomsen MF, Mitchell DG, et al., 2015, Field dipolarization in Saturn's magnetotail with planetward ion flows and energetic particle flow bursts: Evidence of quasi-steady reconnection, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 3603-3617, ISSN: 2169-9402
We present a case study of an event from 20 August (day 232) of 2006, when the Cassini spacecraft was sampling the region near 32 RS and 22 h LT in Saturn's magnetotail. Cassini observed a strong northward-to-southward turning of the magnetic field, which is interpreted as the signature of dipolarization of the field as seen by the spacecraft planetward of the reconnection X line. This event was accompanied by very rapid (up to ~1500 km s−1) thermal plasma flow toward the planet. At energies above 28 keV, energetic hydrogen and oxygen ion flow bursts were observed to stream planetward from a reconnection site downtail of the spacecraft. Meanwhile, a strong field-aligned beam of energetic hydrogen was also observed to stream tailward, likely from an ionospheric source. Saturn kilometric radiation emissions were stimulated shortly after the observation of the dipolarization. We discuss the field, plasma, energetic particle, and radio observations in the context of the impact this reconnection event had on global magnetospheric dynamics.
Yates JN, Southwood DJ, Dougherty MK, 2015, Magnetic phase structure of Saturn's 10.7h oscillations, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 2631-2648, ISSN: 2169-9380
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- Citations: 6
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
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- Citations: 37
Mitchell DG, Brandt PC, Carbary JF, et al., 2015, Injection, Interchange, and Reconnection: Energetic Particle Observations in Saturn's Magnetosphere, MAGNETOTAILS IN THE SOLAR SYSTEM, Editors: Keiling, Jackman, Delamere, Publisher: BLACKWELL SCIENCE PUBL, Pages: 327-343, ISBN: 978-1-118-84234-8
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- Citations: 35
Arridge CS, Achilleos N, Agarwal J, et al., 2014, The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets, PLANETARY AND SPACE SCIENCE, Vol: 104, Pages: 122-140, ISSN: 0032-0633
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- Citations: 48
Hunt GJ, Cowley SWH, Provan G, et al., 2014, Field-aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, ISSN: 2169-9380
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- Citations: 85
Nordheim TA, Jones GH, Roussos E, et al., 2014, Detection of a strongly negative surface potential at Saturn's moon Hyperion, Geophysical Research Letters, Vol: 41, Pages: 7011-7018, ISSN: 1944-8007
On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn’s small, irregularlyshaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS),part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating fromthe direction of the moon’s surface. Plasma wave activity detected by the Radio and Plasma Wave instrumentsuggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and theMagnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that themoon and the spacecraft were magnetically connected when the field-aligned electron population wasobserved. We show that this constitutes a remote detection of a strongly negative (~ 200 V) surface potentialon Hyperion, consistent with the predicted surface potential in regions near the solar terminator.
Jinks SL, Bunce EJ, Cowley SWH, et al., 2014, Cassini multi-instrument assessment of Saturn's polar cap boundary, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 8161-8177, ISSN: 2169-9380
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- Citations: 31
Provan G, Lamy L, Cowley SWH, et al., 2014, Planetary period oscillations in Saturn's magnetosphere: Comparison of magnetic oscillations and SKR modulations in the postequinox interval, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, ISSN: 2169-9380
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- Citations: 43
Sulaiman AH, Masters A, Dougherty MK, et al., 2014, The magnetic structure of Saturn's magnetosheath, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 5651-5661, ISSN: 2169-9380
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- Citations: 20
Jackman CM, Slavin JA, Kivelson MG, et al., 2014, Saturn's dynamic magnetotail: A comprehensive magnetic field and plasma survey of plasmoids and traveling compression regions and their role in global magnetospheric dynamics, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 5465-5494, ISSN: 2169-9380
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- Citations: 63
McAndrews HJ, Thomsen MF, Arridge CS, et al., 2014, Plasma in Saturn's nightside magnetosphere and the implications for global circulation (vol 57, pg 1714, 2009), PLANETARY AND SPACE SCIENCE, Vol: 97, Pages: 86-87, ISSN: 0032-0633
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- Citations: 5
Nichols JD, Badman SV, Baines KH, et al., 2014, Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope, Geophysical Research Letters, Vol: 41, Pages: 3323-3330, ISSN: 1944-8007
We present observations of significant dynamics within two UV auroral storms observedon Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroralemission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330%rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, burstyreconnection of lobe flux in the magnetotail, providing strong evidence that Saturn’s auroral storms arecaused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that theemission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroralform with the upward field-aligned continuity currents flowing into the associated partial ring current.
Simon S, Saur J, van Treeck SC, et al., 2014, Discontinuities in the magnetic field near Enceladus, GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 3359-3366, ISSN: 0094-8276
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- Citations: 12
Bunce EJ, Grodent DC, Jinks SL, et al., 2014, Cassini nightside observations of the oscillatory motion of Saturn's northern auroral oval, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 3528-3543, ISSN: 2169-9380
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- Citations: 17
Kriegel H, Simon S, Meier P, et al., 2014, Ion densities and magnetic signatures of dust pickup at Enceladus, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2740-2774, ISSN: 2169-9380
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- Citations: 36
Pilkington NM, Achilleos N, Arridge CS, et al., 2014, Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2858-2875, ISSN: 2169-9380
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- Citations: 20
Meredith CJ, Alexeev II, Badman SV, et al., 2014, Saturn's dayside ultraviolet auroras: Evidence for morphological dependence on the direction of the upstream interplanetary magnetic field, Journal of Geophysical Research: Space Physics, Vol: 119, Pages: 1994-2008, ISSN: 2169-9402
We examine a unique data set from seven Hubble Space Telescope (HST) “visits” that imagedSaturn’s northern dayside ultraviolet emissions exhibiting usual circumpolar “auroral oval” morphologies,during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn’s bow shock overintervals of several hours. The auroras generally consist of a dawn arc extending toward noon centered near~15° colatitude, together with intermittent patchy forms at ~10° colatitude and poleward thereof, locatedbetween noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, andintensity, which have no clear relationship with the concurrent IMF. However, the patchy postnoon aurorasare found to relate to the (suitably lagged and averaged) IMF Bz, being present during all four visits withpositive Bz and absent during all three visits with negative Bz. The most continuous such forms occur in thecase of strongest positive Bz. These results suggest that the postnoon forms are associated with reconnectionand open flux production at Saturn’s magnetopause, related to the similarly interpreted bifurcated auroral arcstructures previously observed in this local time sector in Cassini Ultraviolet Imaging Spectrograph data,whose details remain unresolved in these HST images. One of the intervals with negative IMF Bz howeverexhibits a prenoon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence ofsignificant IMF dependence in the morphology of Saturn’s dayside auroras.
Masters A, Fujimoto M, Hasegawa H, et al., 2014, Can magnetopause reconnection drive Saturn's magnetosphere?, GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 1862-1868, ISSN: 0094-8276
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- Citations: 22
Jasinski JM, Arridge CS, Lamy L, et al., 2014, Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft, Geophysical Research Letters, Vol: 41, Pages: 1382-1388, ISSN: 1944-8007
We report on the first analysis of magnetospheric cusp observations at Saturn by multiple insitu instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection wasoccurring at Saturn’s magnetopause. This agrees with remote observations that showed the associatedauroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along apoleward trajectory. The spacecraft observed ion energy-latitude dispersions—a characteristic signature ofthe terrestrial cusp. This ion dispersion is “stepped,” which shows that the reconnection is pulsed. The ionenergy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnectionsite varies between ∼27 and 51 RS. An intensification of lower frequencies of the Saturn kilometricradiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphereand providing more favorable conditions for magnetopause reconnection.
Mistry R, Dougherty MK, Masters A, et al., 2014, Separating drivers of Saturnian magnetopause motion, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 1514-1522, ISSN: 2169-9380
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- Citations: 5
Simon S, Neubauer FM, Wennmacher A, et al., 2014, Variability of Titan's induced magnetotail: Cassini magnetometer observations, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 2024-2037, ISSN: 2169-9380
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- Citations: 7
Andriopoulou M, Roussos E, Krupp N, et al., 2014, Spatial and temporal dependence of the convective electric field in Saturn's inner magnetosphere, ICARUS, Vol: 229, Pages: 57-70, ISSN: 0019-1035
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- Citations: 34
Masters A, Phan TD, Badman SV, et al., 2014, The plasma depletion layer in Saturn's magnetosheath, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 121-130, ISSN: 2169-9380
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- Citations: 15
Masters A, Stawarz L, Fujimoto M, et al., 2013, <i>In situ</i> observations of high-Mach number collisionless shocks in space plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 55, ISSN: 0741-3335
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- Citations: 7
Grasset O, Bunce EJ, Coustenis A, et al., 2013, Review of Exchange Processes on Ganymede in View of Its Planetary Protection Categorization, ASTROBIOLOGY, Vol: 13, Pages: 991-1004, ISSN: 1531-1074
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- Citations: 9
Jackman CM, Achilleos N, Cowley SWH, et al., 2013, Auroral counterpart of magnetic field dipolarizations in Saturn's tail, PLANETARY AND SPACE SCIENCE, Vol: 82-83, Pages: 34-42, ISSN: 0032-0633
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- Citations: 51
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