Dynamics of Saturn's Magnetosphere from MIMI During Cassini's Orbital Insertion

Krimigis, S. M.; Mitchell, D. G.; Hamilton, D. C.; Krupp, N.; Livi, S.; Roelof, E. C.; Dandouras, I.; Armstrong, T. P.; Mauk, B. H.; Paranicas, C.; Brandt, P. C.; Bolton, S. J.; Cheng, A. F.; Choo, T.; Gloeckler, G.; Hayes, J. R.; Hsieh, K. C.; Ip, W.-H.; Jaskulek, S.; Keath, E. P.; Kirsch, E.; Kusterer, M. B.; Lagg, A.; Lanzerotti, L. J.; LaVallee, David; Manweiler, J. W.; McEntire, R. W.; Rasmuss, W.; Saur, Joachim; Turner, F. S.; Williams, D. J.; Woch, J.

doi:10.1126/science.1105978

Cited by 164 publications

(146 citation statements)

References 15 publications

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“…Substantial electron fluxes in the 100 eV -2 keV energy range are present with measurable fluxes persisting up to energies of several keV. The Cassini MIMI instrument observed electrons with energies of many tens of keV near T5 (Krimigis et al 2005). When the spacecraft is sunlit the CAPS ELS observes spacecraft photoelectrons with energies less than about 5 eV, but for T5 this population disappeared when Cassini went through Titan's shadow in the time period near CA.…”

Section: Magnetospheric Electrons As a Source Of Titan's Ionospherementioning

confidence: 99%

“…Energetic electrons were observed in Saturn's outer magnetosphere by Voyager (Schardt et al 1984) and by both the CAPS ELS (Coates et al 2007b) and MIMI (Krimigis et al 2005) instruments onboard Cassini. Cravens et al (2006) suggested that incident electrons with a broad range of energies (25 eV -2000 keV) were needed to explain the ionospheric densities measured by the RPWS/LP and INMS during T5, and this has been confirmed by detailed calculations by Agren et al (2007).…”

Section: Introductionmentioning

confidence: 99%

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Model-data comparisons for Titan's nightside ionosphere

Cravens

Robertson

Waite

et al. 2009

Icarus

112

144

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Solar and x-ray radiation and energetic plasma from Saturn's magnetosphere interact with the upper atmosphere producing an ionosphere at Titan. The highly coupled ionosphere and upper atmosphere system mediates the interaction between Titan and the external environment.A model of Titan's nightside ionosphere will be described and the results compared with data from the Ion and Neutral Mass Spectrometer (INMS) and the Langmuir probe (LP) part of the Radio and Plasma Wave (RPWS) experiment for the T5 and T21 nightside encounters of the Cassini Orbiter with Titan.Electron impact ionization associated with the precipitation of magnetospheric electrons into the upper atmosphere is assumed to be the source of the nightside ionosphere, at least for altitudes above 1000 km. Magnetospheric electron fluxes measured by the Cassini electron spectrometer (CAPS ELS) are used as an input for the model. The model is used to interpret the observed composition and structure of the T5 and T21 ionospheres. The densities of many ion species (e.g., CH 5 + and C 2 H 5 + ) measured during T5 exhibit temporal and/or spatial variations apparently associated with variations in the fluxes of energetic electrons that precipitate into the atmosphere from Saturn's magnetosphere.

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Section: Magnetospheric Electrons As a Source Of Titan's Ionospherementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Model-data comparisons for Titan's nightside ionosphere

Cravens

Robertson

Waite

et al. 2009

Icarus

112

144

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“…Bunce et al, 2005;Dougherty et al, 2005;Gurnett et al, 2005;Young et al, 2005), now also including energetic neutral atom imaging of magnetospheric dynamics (e.g. Krimigis et al, 2005;Paranicas et al, 2005). Information on global dynamics can also be obtained from studies of polar UV auroras observed by the Hubble Space Telescope (HST), at both Jupiter (e.g.…”

Section: Introductionmentioning

confidence: 99%

Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines

2007

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Abstract. We consider the contribution of the solar winddriven Dungey-cycle to flux transport in Jupiter's and Saturn's magnetospheres, the associated voltages being based on estimates of the magnetopause reconnection rates recently derived from observations of the interplanetary medium in the vicinity of the corresponding planetary orbits. At Jupiter, the reconnection voltages are estimated to be ∼150 kV during several-day weak-field rarefaction regions, increasing to ∼1 MV during few-day strong-field compression regions.The corresponding values at Saturn are ∼25 kV for rarefaction regions, increasing to ∼150 kV for compressions. These values are compared with the voltages associated with the flows driven by planetary rotation. Estimates of the rotational flux transport in the "middle" and "outer" magnetosphere regions are shown to yield voltages of several MV and several hundred kV at Jupiter and Saturn respectively, thus being of the same order as the estimated peak Dungeycycle voltages. We conclude that under such circumstances the Dungey-cycle "return" flow will make a significant contribution to the flux transport in the outer magnetospheric regions. The "return" Dungey-cycle flows are then expected to form layers which are a few planetary radii wide inside the dawn and morning magnetopause. In the absence of significant cross-field plasma diffusion, these layers will be characterized by the presence of hot light ions originating from either the planetary ionosphere or the solar wind, while the inner layers associated with the Vasyliunas-cycle and middle magnetosphere transport will be dominated by hot heavy ions originating from internal moon/ring plasma sources. The temperature of these ions is estimated to be of the order of a few keV at Saturn and a few tens of keV at Jupiter, in both layers.

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“…Dougherty et al, 2005;Krimigis et al, 2005;Young et al, 2005), by ground-based IR Doppler measurements of ionospheric flows (Stallard et al, 2004), and by studies of the planet's aurorae using the Hubble Space Telescope (HST) (e.g. Gérard et al, 1995Gérard et al, , 2004Cowley et al, 2004a;Prangé et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

Jackman

Cowley²

2006

Ann. Geophys.

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Abstract.We propose a simple model of the flow and currents in Saturn's polar ionosphere. This model is motivated by theoretical reasoning, and guided quantitatively by in situ field and flow data from space missions, ground-based IR Doppler measurements, and Hubble Space Telescope images. The flow pattern consists of components which represent (1) plasma sub-corotation in the middle magnetosphere region resulting from plasma pick-up and radial transport from internal sources; (2) the Vasyliunas-cycle of internal plasma mass-loss down the magnetospheric tail at higher latitudes; and (3) the polar Dungey-cycle flow driven by the solar wind interaction. Upstream measurements of the interplanetary magnetic field (IMF) indicate the occurrence of both extended low-field rarefaction intervals with essentially negligible Dungey-cycle flow, and few-day high-field compression regions in which the Dungey-cycle voltage peaks at a few hundred kV. Here we model the latter conditions when the Dungey-cycle is active, advancing on previous axisymmetric models which may be more directly applicable to quiet conditions. For theoretical convenience the overall flow pattern is constructed by adding together two components -a purely rotational flow similar to previous axisymmetric models, and a sun-aligned twin vortex representing the dawn-dusk asymmetry effects associated with the Vasyliunas-and Dungey-cycle flows. We calculate the horizontal ionospheric current associated with the flow and the field-aligned current from its divergence. These calculations show that a sheet of upward-directed field-aligned current flows at the boundary of open field lines which is strongly modulated in local-time by the Dungey-cycle flows. We then consider implications of the field-aligned current for magnetospheric electron acceleration and aurorae using two plasma source populations (hot outer magnetospheric electrons and cool dense magnetosheath electrons). Both sources displayCorrespondence to: C. M. Jackman (cj47@ion.le.ac.uk) a strong dawn-dusk asymmetry in the accelerating voltages required and the energy fluxes produced, resulting from the corresponding asymmetry in the current. The auroral intensities for the outer magnetosphere source are typically ∼50 kR at dawn and ∼5 kR at dusk, in conformity with recent auroral observations under appropriate conditions. However, those for the magnetosheath source are much smaller. When the calculated precipitating electron energy flux values are integrated across the current layer and around the open closed field line boundary, this yields total UV output powers of ∼10 GW for the hot outer magnetosphere source, which also agrees with observations.

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Dynamics of Saturn's Magnetosphere from MIMI During Cassini's Orbital Insertion

Cited by 164 publications

References 15 publications

Model-data comparisons for Titan's nightside ionosphere

Model-data comparisons for Titan's nightside ionosphere

Significance of Dungey-cycle flows in Jupiter's and Saturn's magnetospheres, and their identification on closed equatorial field lines

A model of the plasma flow and current in Saturn's polar ionosphere under conditions of strong Dungey cycle driving

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