SM32A-01

Longitudinal variations in Saturn's magnetosphere caused by hot electrons.

* Bagenal, F bagenal@colorado.edu, University of Colorado, UCB 392 LASP, Boulder, CO 80302,
Fleshman, B bobby.fleshman@colorado.edu, University of Oklahoma, Dept of Physics and Astronomy, Norman, OK 73019,
Fleshman, B bobby.fleshman@colorado.edu, University of Colorado, UCB 392 LASP, Boulder, CO 80302,
Delamere, P peter.delamere@colorado.edu, University of Colorado, UCB 392 LASP, Boulder, CO 80302,
Williams, J john2.williams@umontana.edu, University of Montana, Dept Physics, Missoula, MT 59812,

A non-thermal tail to the electron distribution function has been measured in the inner magnetospheres of both Jupiter and Saturn. These hot electrons are only a small fraction of the total electron density, yet their influence on the gas tori at Jupiter and Saturn is significant. We explore the role of hot electrons at Saturn using a water group-based homogeneous physical chemistry model. Our results suggest the energy input to Saturn's inner magnetosphere is negligible, but that the hot electrons are a significant source of ionization. We propose that the observed azimuthal electron density modulation at Saturn between 3 and 5 Rs is caused by an azimuthally varying hot electron abundance. In addition, we will explore longitudinal variations in composition and compare with a recent analysis of the Cassini Plasma Spectrometer (CAPS) data.

SM32A-02

Suprathermal Heavy Ion Composition in Saturn's Magnetosphere

* Hamilton, D C dch@umd.edu, University of Maryland, Department of Physics, College Park, MD 20742, United States
DiFabio, R D rdifabio@umd.edu, University of Maryland, Department of Physics, College Park, MD 20742, United States
Christon, S P spchriston@aol.com, Focused Analysis and Research, Columbia, Columbia, MD 21044, United States
Krimigis, S M tom.krimigis@jhuapl.edu, Academy of Athens, Athens, Athens, 10679, Greece
Krimigis, S M tom.krimigis@jhuapl.edu, Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, United States
Mitchell, D G don.mitchell@jhuapl.edu, Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, United States
Dandouras, I Iannis.Dandouras@cesr.fr, Centre D'Etude Spatiale Des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31028, France

We use measurements from the Charge-Energy-Mass Spectrometer (CHEMS) to determine long-term average heavy ion composition in Saturn's magnetosphere. CHEMS, one of three sensors comprising the MIMI investigation on Cassini, determines the mass and charge state of ions in the energy per charge range 3-220 keV/e. With four years of data now in hand since Cassini entered into orbit about Saturn, it is possible to determine average magnetospheric abundances including even relatively rare species. In order to definitively identify each species we utilize data above 80 keV/e where all species considered are positively identified by both a time-of-flight and an energy measurement, yielding separately an ion's mass per charge and mass. We will present abundances of C⁺, N⁺, O⁺, O⁺⁺, OH⁺, H₂O⁺, N₂⁺ (or possibly CO⁺), and O₂⁺. O⁺ is the most abundant suprathermal heavy ion with an abundance comparable to that of H⁺. C⁺ and N⁺ are present at 2-5% of O⁺ while O₂⁺ is present at a little over 1% of O⁺. We will discuss the implications of these abundances for plasma source strengths, acceleration processes, and magnetospheric residence times.

SM32A-03

Energetic Charged Particle Injections at Saturn

* Paranicas, C chris.paranicas@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Mitchell, D G donald.g.mitchell@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Hamilton, D C dch@umd.edu, University of Maryland, Department of Physics, College Park, MD 20742, United States
Krimigis, S M stamatios.krimigis@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Mauk, B H barry.mauk@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Brandt, P C pontus.brandt@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Carbary, J F jim.carbary@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States
Rymer, A M abi.rymer@jhuapl.edu, Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723, United States

The Cassini spacecraft has been in Saturn orbit for over 4 years. The Magnetospheric Imaging Instrument (MIMI) is a charged and neutral particle instrument with three separate sensors. On every perigee pass to date, data taken by MIMI reveal the presence of very recent and/or older charged particle injections. For our purposes, injections are spatially confined populations whose fluxes are recognizably greater than the fluxes of the ambient population. These populations are transient in nature and our previous work and the work of others has shown that they evolve essentially through the usual corotation and gradient-curvature drifts. However, it is not completely understood whether all of the injections observed by MIMI, in the few keV to MeV energy range, are associated with the same physical mechanism. Injections can, in principle, be caused by local accelerations of a fraction of the denser, lower energy particles. On the other hand, injections may also be associated with processes that transport particles radially, such as in magnetospheric flux tube interchange or large scale magnetospheric reconfigurations. In this paper, we will present a survey of the data set, an organization of the injections by their properties, and some hypotheses about how these properties reveal information about the underlying physical generation mechanisms.

SM32A-04

Structure, Variation and Pressure Balance in the Saturnian Plasma Sheet. Combined MIMI, CAPS and MAG Measurements From Cassini

* Sergis, N nsergis@phys.uoa.gr, Office of Space Research and Technology, Academy of Athens, 4, Soranou Efessiou St., Athens, 11527, Greece
Arridge, C S csa@mssl.ucl.ac.uk, Centre for Planetary Sciences, University College London, Gower Street, London., London, WC1E 6BT, United Kingdom
Arridge, C S csa@mssl.ucl.ac.uk, Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey., Surrey, RH5 6NT, United Kingdom
Krimigis, S M Tom.Krimigis@jhuapl.edu, The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD., Laurel, 20723-6099, United States
Krimigis, S M Tom.Krimigis@jhuapl.edu, Office of Space Research and Technology, Academy of Athens, 4, Soranou Efessiou St., Athens, 11527, Greece
Mitchell, D G Don.Mitchell@jhuapl.edu, The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD., Laurel, 20723-6099, United States
Rymer, A M Abigail.Rymer@jhuapl.edu, The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD., Laurel, 20723-6099, United States
Hamilton, D C dch@umd.edu, Department of Physics, University of Maryland, Physics Building, College Park, MD., College Park, 20742, United States
Krupp, N krupp@LINMPI.MPG.DE, Max Planck Institute for Solar System Research, Max Planck Str. 2, Katlenburg-Lindau., Lindau, 37191, Germany
Roelof, E C Edmond.Roelof@jhuapl.edu, The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD., Laurel, 20723-6099, United States
Dougherty, M K m.dougherty@imperial.ac.uk, Space and Atmospheric Physics Group, Imperial College, Huxley Building, Imperial College, South Kensington., London, SW7 2AZ, United Kingdom
Coates, A J ajc@mssl.ucl.ac.uk, Centre for Planetary Sciences, University College London, Gower Street, London., London, WC1E 6BT, United Kingdom
Coates, A J ajc@mssl.ucl.ac.uk, Mullard Space Science Laboratory, University College London, Holmbury St. Mary Dorking, Surrey., Surrey, RH5 6NT, United Kingdom

Combined plasma, energetic particle and magnetic field measurements, obtained by the Magnetospheric Imaging Instrument (MIMI), the Cassini Plasma Spectrometer (CAPS) sensors and the magnetometer (MAG) respectively, are used to study the Saturnian plasma sheet as revealed through 2 nearly vertical passes of Cassini (days 8/2007 to 42/2007) during its high latitude orbits. Trajectories of such geometry favor the clear detection of the plasma sheet boundaries, both through magnetic field and particle data. As the in-situ Cassini measurements offer complete energy coverage (eV to MeV) of the cold plasma and the energetic particle population, where present, the computation of the particle temperature and total plasma pressure is made possible. The extent and temporal variation of the plasma sheet is examined, and its scale height is calculated for the cold plasma and the energetic particle population, using different methods (e.g. exponential decay, Harris profile), per ion specie where possible. Initial results indicate that the dayside plasma sheet is wide in latitude (±45 deg) and extends up to the magnetopause, with its pressure decreasing with radial distance. The night side plasma sheet appears to be much thinner, with a larger scale height for energetic ions (2Rs) compared to the cold-warm plasma (1Rs). Plasma beta is kept close to or above 1 inside the plasma sheet region, outside ~8 Rs. Furthermore, based on combined plasma density, particle pressure and magnetic field measurements, the stress balance inside the plasma sheet is also addressed.

SM32A-05

Energetic Ions and Magnetic Fields Upstream From the Kronian Magnetosphere

* Krimigis, S M tom.krimigis@jhuapl.edu, Office for Space Research and Technology. Academy of Athens, Soranou Efesiou 4, Athens, 11527, Greece
* Krimigis, S M tom.krimigis@jhuapl.edu, Applied Physics Laboratory The Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
Sarris, E sarris@ee.duth.gr, Demokritos University of Thrace, Vassilissis Sofias Street, Xanthi, 67100, Greece
Sergis, N nsergis@phys.uoa.gr, Office for Space Research and Technology. Academy of Athens, Soranou Efesiou 4, Athens, 11527, Greece
Dialynas, K kdialynas@phys.uoa.gr, Office for Space Research and Technology. Academy of Athens, Soranou Efesiou 4, Athens, 11527, Greece
Mitchell, D G Don.Mitchell@jhuapl.edu, Applied Physics Laboratory The Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
Hamilton, D C dch@umd.edu, Department of Physics University of Maryland, 2108 Mitchell Bldg, College Park, MD 20742, United States
Dougherty, M m.dougherty@imperial.ac.uk, Space and Atmosheric Physics Group, Imperial College, Exhibition Road, South Kensington, London, SW72DD, United Kingdom

The existence of energetic particle events to ~200 Rs upstream and ~1300 Rs downstream of Saturn was established during the Voyager 1, 2 flybys in 1980 and 1981, respectively. The origin of the events could not be determined with certainty because of lack of particle charge state and species measurements at lower (<300 keV) energies, which dominate the spectra. High sensitivity observations of energetic ion directional intensities, energy spectra, and ion composition were obtained by the Ion and Neutral Camera (INCA) of the MIMI instrument complement with a geometry factor of ~2.5 cm² sr and some capability of separating light (H, He) and heavier (C, N, O) ion groups (henceforth referred to as "hydrogen" and "oxygen" respectively). Charge state information was provided where possible by the Charge-Energy-Mass-Spectrometer (CHEMS) over the range ~3 to 220 keV per charge, and magnetic field (IMF) data by the MAG instrument on Cassini. The observations revealed the presence of distinct upstream bursts of energetic hydrogen and oxygen ions whenever the IMF connected the spacecraft to the planetary bow shock, up to distances of 135 RS. The events exhibited the following characteristics: (1) Hydrogen ion bursts are observed in the energy range 3 to 220 keV (and occasionally to E > 220 keV) and oxygen ion bursts in the energy range 32 to -300 keV. (2) Particle onsets are nearly field-aligned, but the distribution tends to isotropize as the event progresses in time. (3) The duration of the ion bursts is several minutes up to 4 hrs. (4) The events are of varying composition, with some exhibiting significant fluxes of oxygen. (5) The bursts have a filamentary structure with some exhibiting distinct signatures of "velocity- filtering effects" at the edges of convecting IMF filaments. (6) Some ion bursts are accompanied by distinct diamagnetic field depressions and exhibit wave structures consistent with ion cyclotron waves for H+, and O+. Given the repeated magnetic field configuration during the detection of the events and that energetic ions trapped within the magnetosphere of Saturn are mostly H+ and O+ we conclude that O+-rich upstream events must be particles leaking from Saturn's magnetosphere under favorable IMF conditions. The spectral evolution of the upstream events and their anisotropy characteristics will be presented and discussed in the context of current models.

SM32A-06

Plasma Flow in Jupiter's Inner and Middle Magnetosphere

* Paterson, W R bill.paterson@hamptonu.edu, Hampton University, Department of Atmospheric and Planetary Sciences, Hampton, VA 23668, United States

Measurements of the thermal ion component of the plasmas acquired with the Galileo spacecraft at Jupiter are examined for evidence of the patterns of flow existing in the plasma torus and the middle magnetosphere. The observations are of interest because they provide constraints for models addressing transport and circulation of particles and magnetic flux. Plasma transport is believed to be important in development of Jupiter's main ring of auroral luminosity, which has been studied extensively in telescopic observations, and which will be investigated during the Juno mission. Features of interest in the Galileo observations include regions of both outward and inward radial flow. Additionally, there is an apparent decline with radial distance from Jupiter in the component of velocity aligned with corotation, followed by an apparent recovery as distance further increases. In this presentation, these observations are discussed and compared with expectations based on models of magnetospheric circulation, models of the coupling of the ionosphere to the magnetosphere associated with the aurora, and prior observations from the Voyager spacecraft.

SM32A-07

Z-Mode Waves as the Source of Saturn Narrowband Radio Emissions

* Ye, S shengyi-ye@uiowa.edu, University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
Menietti, J D john-menietti@uiowa.edu, University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
Fischer, G georg.fischer@oeaw.ac.at, Austrian Academy of Sciences, Space Research Inst., Graz, A-8010, Austria
Gurnett, D A donald-gurnett@uiowa.edu, University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
Kurth, W S william-kurth@uiowa.edu, University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
Wang, Z zhenzhen-wang@uiowa.edu, University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States

We report ~5 kHz narrowband Z-mode emissions observed by the Cassini Radio Plasma Wave Science (RPWS) instrument during high latitude perikrone passes. The narrowband emissions observed below the local electron cyclotron frequency (f_ce) are >20 dB more intense than the usual L-O mode narrowband emissions observed above local f_ce. Polarization measurements show that the narrowband emissions observed below f_ce are oppositely polarized to those above f_ce, which identifies the emissions below fce as Z-mode waves. We propose that the L-O mode narrowband emissions observed at ~5 kHz are mode converted from the Z-mode waves at a density gradient or density irregularity. The Z- mode to O-mode conversion via scattering off of density irregularities can also account for the direction finding results of ~5 kHz narrowband emissions that cannot be explained by the model in Ye et al. [2008], where narrowband emissions are first generated as electrostatic upper hybrid waves when the matching condition f_UH = (n+1/2)f_ce is satisfied.

SM32A-08

Kelvin-Helmholtz Instability at the Dawn Flank of Saturn's Magnetopause

* Masters, A adam.masters02@imperial.ac.uk, Imperial College London, Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2BW, United Kingdom
Achilleos, N nick@apl.ucl.ac.uk, University College London, Atmospheric Physics Laboratory, Department of Physics and Astrononmy, University College London, Gower Street, London, WC1E 6BT, United Kingdom
Bertucci, C cbertucci@iafe.uba.ar, IAFE, Institute for Astronomy and Space Physics, PO Box 67 - Suc. 28, Buenos Aires, C1428ZAA, Argentina
Bertucci, C cbertucci@iafe.uba.ar, Imperial College London, Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2BW, United Kingdom
Dougherty, M K m.dougherty@imperial.ac.uk, Imperial College London, Space and Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2BW, United Kingdom
Kanani, S sk2@mssl.ucl.ac.uk, University College London, Centre for Planetary Sciences, University College London, London, WC1E 6BT, United Kingdom
Kanani, S sk2@mssl.ucl.ac.uk, Mullard Space Science Laboratory, Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, United Kingdom
Arridge, C S csa@mssl.ucl.ac.uk, University College London, Centre for Planetary Sciences, University College London, London, WC1E 6BT, United Kingdom
Arridge, C S csa@mssl.ucl.ac.uk, Mullard Space Science Laboratory, Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, United Kingdom
McAndrews, H J hazelm@lanl.gov, Los Alamos National Laboratory, Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
Sittler, E C Edward.C.Sittler@nasa.gov, NASA GSFC, Heliophysics Science Division, NASA GSFC, Greenbelt, MD 20771, United States
Coates, A J ajc@mssl.ucl.ac.uk, University College London, Centre for Planetary Sciences, University College London, London, WC1E 6BT, United Kingdom
Coates, A J ajc@mssl.ucl.ac.uk, Mullard Space Science Laboratory, Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, United Kingdom

Crossings of Saturn's magnetopause made by the Cassini spacecraft between 12 and 17 March 2006 are analysed. Magnetic field and plasma data are used to identify excursions into the magnetosheath bounded by crossings of the magnetopause current layer. During most of this period Cassini's trajectory was approximately parallel to the magnetopause boundary given by a model of the surface. Minimum variance analysis (MVA) of the magnetic field vector measurements is used to determine the normal to the boundary for each crossing of the current layer. The normals corresponding to the crossings made on 12, 13 and 17 March oscillate about the normal predicted by the surface model. This suggests the presence of regular boundary waves with a direction of propagation found to be close to parallel to Saturn's rotational equator, and not coincident with the expected solar wind flow direction in the local magnetosheath. Based on this propagation direction and the magnetospheric and magnetosheath magnetic fields we propose that these waves were generated by the Kelvin-Helmholtz instability. In addition we discuss the possibility that on 15 and 16 March nonlinear Kelvin-Helmholtz waves produced a strongly perturbed magnetopause boundary that may have led to local magnetic reconnection.

Authors (2008), Title, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract xxxxx-xx