P53D-01 

High Latitude Structure of Saturn's Magnetopause: Cassini Observations

* Achilleos, N (nick@apl.ucl.ac.uk), Atmospheric Physics Laboratory, University College London, Gower Street, London, Eng WC1E 6BT, United Kingdom Arridge, C S (csa@mssl.ucl.ac.uk), Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Eng RH5 6NT, United Kingdom McAndrews, H J (hazelm@lanl.gov), Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545, United States Masters, A (adam.masters02@imperial.ac.uk), Blackett Laboratory, Imperial College London, Exhibition Road, LONDON, Eng SW7 2AZ, United Kingdom Dougherty, M K (m.dougherty@imperial.ac.uk), Blackett Laboratory, Imperial College London, Exhibition Road, LONDON, Eng SW7 2AZ, United Kingdom Coates, A J (ajc@mssl.ucl.ac.uk), Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Eng RH5 6NT, United Kingdom

We investigate the location of magnetopause crossings detected during high latitude orbits (> 30 deg) of the Cassini spacecraft. Using the magnetospheric field as a proxy for solar wind pressure, we compare the observed crossing locations with their predicted positions from axisymmetric magnetopause models. Systematic differences at high latitudes between these two quantities are used to place constraints on the degree of polar 'flattening' for Saturn's magnetopause. We comment on the corresponding internal structure of the magnetospheric obstacle.

P53D-02 

Chorus Observations at Saturn

* Hospodarsky, G B (george-hospodarsky@uiowa.edu), University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States Menietti, J D), University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States Averkamp, T F (terrance-averkamp@uiowa.edu), University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States Kurth, W S (william-kurth@uiowa.edu), University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States Gurnett, D A), University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States Dougherty, M K (mdougherty@imperial.ac.uk), Imperial College, Blackett Lab, Space and Atmos. Physics, London, SW7 2BZ, United Kingdom Coates, A J (ajc@mssl.ucl.ac.uk), University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, RH5 6NT, United Kingdom Young, D T), Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78284, United States Rymer, A M (abigail.rymer@jhuapl.edu), Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20707, United States Santolik, O (ondrej.santolik@mff.cuni.cz), Charles University and Institute of Atmospheric Physics, Mathematics and Physics, Prague, CZ-18000, Czech Republic

Whistler mode chorus has been detected by the Radio and Plasma Wave Science (RPWS) Instrument during the majority of Cassini's first fifty orbits of Saturn. At Saturn, chorus is detected in two different regions. The most common observations are of chorus propagating away from Saturn's magnetic equator, suggesting a source near the magnetic equator. This chorus is usually detected for many hours, is only observed below half the electron cyclotron frequency, occurs primarily from L shells of about 5 to 8, and shows no obvious correlation with Saturn latitude or local time. Higher resolution measurements show that the fine structure of this chorus consists of larger time scales (tens of seconds to minutes) than detected at the Earth (< 1 second). The second region of chorus detected at Saturn is in association with local plasma injections. For many of the plasma injection events, intense chorus emissions are detected both above and below half the electron cyclotron frequency, with a gap in the emission at half the cyclotron frequency. This chorus also shows fine structure at a much smaller time scale (< 1 second), and overall, the structure of the chorus appears similar to chorus detected at the Earth. The properties and characteristics of the chorus detected during the first fifty orbits of Cassini will be discussed, and the similarities and differences of the two types of chorus detected at Saturn will be examined.

P53D-03 

Suprathermal Heavy Ion Variations in the <20 Rs Kronian Magnetosphere

* Christon, S P (spchriston@aol.com), Focused Analysis and Research, Columbia, Columbia, MD 21044, United States Hamilton, D C (dch@umd.edu), University of Maryland, College Park, College Park, MD 20742, United States Carbary, J F (jim.carbary@jhuapl.edu), JHU/APL, Laurel, Laurel, MD 20723, United States Krimigis, S M (tom.krimigis@jhuapl.edu), JHU/APL, Laurel, Laurel, MD 20723, United States Mitchell, D G (don.mithchell@jhuapl.edu), JHU/APL, Laurel, Laurel, MD 20723, United States Paranicas, C (chris.paranicas@jhuapl.edu), JHU/APL, Laurel, Laurel, MD 20723, United States Rymer, A M (abi.rymer@jhuapl.edu), JHU/APL, Laurel, Laurel, MD 20723, United States

Singly charged heavy (e.g., O⁺¹, H₂O⁺¹, N₂⁺¹, and O₂⁺¹) and lighter (e.g., H⁺, H₂⁺¹, and He⁺¹) ions in Saturn's magnetosphere are understood to derive predominantly from Saturn and it's rings and satellites. Measurement of these ions and their variations at suprathermal energies provides information on the effectiveness and nature of acceleration processes at Saturn. On each orbit of Cassini about Saturn, variations in the fluxes and ratios of low charge-state heavies to each other and to lighter ions are measured in the <20 Rs Kronian magnetosphere by the Charge-Energy-Mass Spectrometer CHEMS of the Cassini/MIMI experiment at ~3-220 keV/e. Contributions to these often significant variations may result from varying spatial and temporal aspects of the Kronian magnetosphere and transport processes within it, and/or from active processes and variable sources on Saturn, it's rings, and/or satellites (e.g., Enceladus' plume dynamics). Separation of spatial from temporal variations is important in determining global patterns of suprathermal ion abundance, acceleration, and transport. For example, measurements from Cassini/MIMI have established that impulsive injections of tens to hundreds of keV energetic ions and electrons are persistent features in Saturn's magnetosphere at R < 20 Rs. As a part of this study, we will attempt to determine the relative effect of such injections on the observed heavy ion fluxes. We will investigate and report on several years' worth of these spatial-temporal variations at Saturn in an effort to identify, resolve, and categorize both repetitive variation patterns (more likely to be spatial in nature) and dynamic variations (more likely to be temporal in nature).

P53D-04 

Energy Spectra and Composition of Particle Injections in Saturn's Magnetosphere

* Hamilton, D (dch@umd.edu), University of Maryland, Department of Physics, College Park, MD 20742, United States DiFabio, R (rdifabio@umd.edu), University of Maryland, Department of Physics, College Park, MD 20742, United States Rymer, A (Abigail.Rymer@jhuapl.edu), Johns Hopkins University, Applied Physics Laboratory, Laruel, MD 20723, United States Krimigis, S (tom.krimigis@jhuapl.edu), Johns Hopkins University, Applied Physics Laboratory, Laruel, MD 20723, United States Mitchell, D (don.mitchell@jhuapl.edu), Johns Hopkins University, Applied Physics Laboratory, Laruel, MD 20723, United States

We use measurements from the Charge-Energy-Mass Spectrometer (CHEMS) to determine the energy spectra and composition of the frequent particle injections observed 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. Frequent impulsive particle injections appear to replenish a ring current that persists outside of about L=7. The ring current spectra, averaged over L=7-11, are typically very good power laws from 3 keV up to 60-100 keV with spectral indices in the range -2.0 to -2.5. The major ion species (protons, singly charged oxygen, and molecular hydrogen) usually have very similar spectral slopes. In this talk we examine the ion spectra in numerous impulsive injections, look for differences among species, and compare with spectra of the persistent ring current in order to investigate acceleration and transport processes in Saturn's magnetosphere.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.