SM52A-01 INVITED 

Solar wind and rotational effects on the 3d configuration of Saturn's magnetosphere: Observations, theory, and modelling, in the Cassini era

* Arridge, C S (chris.arridge@physics.org), Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking, RH5 6NT, United Kingdom Khurana, K K (kkhurana@igpp.ucla.edu), Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Slichter Hall, Los Angeles, CA 90095, United States Russell, C T (ctrussel@igpp.ucla.edu), Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Slichter Hall, Los Angeles, CA 90095, United States Achilleos, N (nick@apl.ucl.ac.uk), Atmospheric Physics Laboratory, University College London, Gower Street, London, WC1E 6BT, United Kingdom Andre, N (nandre@rssd.esa.int), Research and Scientific Support Department, European Space Agency, Keplerlaan 1, Noordwijk, 2200, Netherlands Dougherty, M K (m.dougherty@ic.ac.uk), Space and Atmospheric Physics, The Blackett Laboratory, Imperial College London, South Kensington, London, SW7 2AZ, United Kingdom McAndrews, H J (hazelm@lanl.gov), Los Alamos National Laboratory, Space Science and Applications (ISR-1), Los Alamos, NM 87545, United States

Cassini has now provided over 50 orbits of high quality data and is revolutionising our understanding of Saturn's magnetosphere. The post-Voyager view was of a magnetosphere somewhat intermediate between the terrestrial and jovian magnetospheres. Cassini observations, and recent modelling and theoretical work, are showing us that the distinction is not so straightforward. Saturn's&pmagnetosphere appears to be unique in the solar system in that the solar wind and rotational effects strongly interact to produce a highly complex magnetosphere. For example, observations have shown (Arridge et al., 2007a) that the magnetodisc is suppressed on the dayside when the magnetosphere is in a compressed state showing that the effect of rotation on the magnetic field (Arridge et al., 2007b; Bunce et al. 2007) can be significantly altered by the solar wind in a highly time-dependent manner. In this talk we discuss the roles of solar wind and rotational forcing in producing the complex three-dimensional kronian magnetosphere. In particular we discuss: the compressibility of the magnetosphere, observations of the polar cusp and evidence for an open magnetosphere, formation of the magnetotail, morphology of the plasma sheet, and magnetodisc models.

SM52A-02 INVITED 

Energetic Particles in Saturn's Magnetotail

* Mitchell, D G (don.mitchell@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Carbary, J F (jim.carbary@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Krupp, N (krupp@linmpi.mpg.de), 4Max-Planck Institut für Sonnensystemforschung, Max-Planck- Strasse 2, Lindau, D-37191, Germany Krimigis, S M (Tom.Krimigis@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Hamilton, D C (dch@umd.edu), Department of Physics, University of Maryland, University Blvd, College Park, MD 20742, United States Kane, M (mark_kane@yahoo.com), Research Consulting Group, Inc., 1411 Saratoga Dr, Bel Air, MD 21014, United States

Energetic particle measurements in Saturn's magnetotail reveal a magnetotail dominated by Saturn's rotational dynamics as far back in the tail as 60 Rs, rarely but sometimes spectacularly disrupted by tail reconnection events. Although Cassini spent little time in the tail, and even less at the location of the tail current sheet, the time spent there revealed a pattern of very regular encounters with the energetic particles that fill the current sheet, usually once every Saturn rotation. Carbary et al. 2007a, b show that energetic electrons reappear every rotation when the spacecraft is sufficiently close to the current sheet location, and further that they lie along a spiral in longitude when mapped into the SKR coordinate system (Kurth et al., 2007). Energetic ions are also observed in the same locations, with a mix of hydrogen and oxygen not very different from that observed in the magnetosphere between 10 and 20 Rs. These ions generally display velocities approximately in the corotation direction, but with magnitudes well below rigid corotation (Kane et al., 2007, manuscript in preparation). Two other classes of energetic particle events are also seen in the magnetotail. The first consists of energetic ion and electron beams, likely accelerated in the auroral zone over downward current regions. The second are those generated in tail reconnection events (e.g., Jackman et al., 2007; Hill et al. 2007). We will give examples of all of these phenomena, including both in situ measurements and ENA images/movies. Carbary, J.~F., Mitchell, D.~G., Krimigis, S.~M., Hamilton, D.~C., Krupp, N., Charged particle periodicities in Saturn's outer magnetosphere, Journal of Geophysical Research (Space Physics) 112, 6246 {2007JGRA..11206246C} 2007a Carbary, J. F., D. G. Mitchell, S. M. Krimigis, and N. Krupp (2007), Evidence for spiral pattern in Saturn's magnetosphere using the new SKR longitudes, Geophys. Res. Lett., 34, L13105, doi:10.1029/2007GL030167 2007b Kurth, W. S., A. Lecacheux, T. F. Averkamp, J. B. Groene, and D. A. Gurnett (2007), A Saturnian longitude system based on a variable kilometric radiation period, Geophys. Res. Lett., 34, L02201, doi:10.1029/2006GL028336. M. Kane, D. G. Mitchell, J. F. Carbary, and S. M. Krimigis, Ion convective anisotropies detected by the Cassini INCA experiment in Saturn's magnetosphere, manuscript in preparation, 2007. Jackman, C. M., C. T. Russell, D. J. Southwood, C. S. Arridge, N. Achilleos, and M. K. Dougherty, (2007), Strong rapid dipolarizations in Saturn's magnetotail: In situ evidence of reconnection, Geophys. Res. Lett., 34, L11203, doi:10.1029/2007GL029764. Hill, T.W., M.F. Thomsen, M.G. Henderson, R.L. Tokar, A.J. Coates, H.J. McAndrews, G.R. Lewis, D.G. Mitchell, C.M. Jackman, F.J. Crary, D.T. Young, M.K. Dougherty, C.T. Russell, (2007), Plasmoids in Saturn's Magnetotail, submitted, J. Geophys. Res., 2007JA012626, 2007.

SM52A-03 

Hot ion Distributions and Anisotropies in the Outer Magnetospheres of Jupiter and Saturn

* Kane, M (mark_kane@yahoo.com), RCG, Inc., 1411 Saratoga Dr., Bel Air, MD 21014, United States Mitchell, D G (donald.g.mitchell@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Carbary, J F (james.carbary@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States Krimigis, S M (tom.krimigis@jhuapl.edu), Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States

The Voyager and Galileo spacecraft detected convecting hot ions in the outer magnetosphere of Jupiter. Both spacecraft revealed a co-rotation dominated plasma disk containing a mixture of light (hydrogen) and heavy (sulfur, oxygen) ions, with the heavy ions contributing the bulk of the pressure. The equatorial outer magnetosphere of Jupiter was in a state of partial co-rotation, with temporal and local time variations apparent. Radial profiles indicate increasing (sub)co-rotation to a distance beyond which the profiles cease their increase. After exiting the magnetodisk region, Voyager 2 traversed a transitional region before finally encountering the dawn magnetopause at a distance of ~170 Jupiter radii and beyond, whereupon it entered a region filled with heavy ion dominated magnetospheric plasma. At Saturn, the Voyager and Cassini spacecraft have measured intensities of hot hydrogen and oxygen ions in the outer magnetosphere. We find that the ion anisotropies in the outer magnetosphere are frequently convective in nature. Analysis of night side ion populations reveals plasma capable of nearly rigid co-rotation within the orbit of Titan, but beyond this distance, we find increasing departure from rigid co-rotation. We find striking similarities in the overall morphology of these systems. We present a comparative analysis of the dynamics of hot ions in the night side outer regions of the magnetospheres of Jupiter and Saturn using a synthesis of our multi-spacecraft observations.

SM52A-04 

Plasma convection at Saturn: how does it work, and what does it affect?

* Farmer, A J (afarmer@cfa.harvard.edu), Harvard University, MS-51, 60 Garden St, Cambridge, MA 02138, United States

The Cassini mission has revealed much about plasma dynamics in Saturn's magnetosphere. It is now clear that there are fundamental differences between the processes occurring in the Kronian and Jovian systems. We examine the observed plasma properties as a function of distance and longitude, and attempt to deduce the nature of the plasma convection occurring at Saturn. In particular, the plasma density asymmetry (reported by Gurnett et al. 2007) and the temperature structure seem difficult to reconcile. We compare with the properties of the Io torus at Jupiter, and investigate whether similar heating mechanisms could be at play in the two magnetospheres. Alternative scenarios will also be presented. A further question concerns the impact of the plasma convection on the observed drift in the period of the SKR. Goldreich & Farmer (2007) proposed that the convection in Saturn's magnetosphere could be responsible for the changing rotation rate. Here we provide an update on the plausibility of the model in the light of the most recent observations.

SM52A-05 

A Statistical Study of Injection/Dispersion Events in Saturn's Inner Magnetosphere

* Chen, Y (yichen@rice.edu), Physics and Astronomy Department, Rice University, 6100 Main Street, Houston, TX 77251-1892, United States Hill, T W (hill@rice.edu), Physics and Astronomy Department, Rice University, 6100 Main Street, Houston, TX 77251-1892, United States

In the inner magnetosphere of a rapidly rotating planet like Jupiter or Saturn, radial transport of plasma is mainly composed of hot, tenuous plasma moving inward and cold, denser plasma moving outward. The drift dispersion of injecting hot plasma provides direct evidence for this convective process. The Cassini Plasma Spectrometer (CAPS) has frequently reported observations of such injection/dispersion events [e.g., Burch et al., 2005 GRL L14S02; Hill et al., 2005 GRL L14S10]. Based on the study of Hill et al., the analysis of the properties of such signatures is continued in this paper, with a much larger data set of 26 Cassini orbits of Saturn, extending from July 2004 to August 2006. A statistical picture of the injection/dispersion characteristics is developed, indicating the distributions of ages, time scales and length scales. Moreover, an interesting rotational modulation of occurrence frequency is present in the Voyager-era Saturn Longitude System (SLS), but not in the Cassini-era Saturn Kilometric Radiation (SKR) system. A periodogram analysis using the Lomb-Scargle algorithm is underway to provide the accurate information of the recurrence period. Preliminary results show multiple-peaks in the period window near 11 hours.

SM52A-06 

Measured Correlations of Auroral Emissions from Jupiter and Saturn With Solar Wind Variations

* Clarke, J T (jclarke@bu.edu), Boston University, 725 Commonwealth Ave, Boston, MA 02215, United States Nichols, J (jdn@bu.edu), Boston University, 725 Commonwealth Ave, Boston, MA 02215, United States Gerard, J (jc.gerard@ulg.ac.be), University of Liege, Allée du 6 Aout, 17, Liege, B-4000, Belgium Grodent, D (d.grodent@ulg.ac.be), University of Liege, Allée du 6 Aout, 17, Liege, B-4000, Belgium Wannawichain, S (suwichaw@bu.edu), Boston University, 725 Commonwealth Ave, Boston, MA 02215, United States Duval, J (jduval@bu.edu), Boston University, 725 Commonwealth Ave, Boston, MA 02215, United States Hansen, K (kenhan@umich.edu), Univ. of Michigan, 2355 Hayward, Ann Arbor, MI 48109, United States

An extended set of Hubble Space Telescope (HST) observations of the UV auroral emissions from Jupiter and Saturn has been carried out in three campaigns over Jan.-June 2007. This is by far the most extensive series of remote high resolution imaging of planetary aurora to date, and provides new physical insight into the cause and effect relationships governing the controlling processes for the giant planet auroral emissions. Simultaneous in situ measurements of local solar wind and magnetospheric plasma conditions have been made during two of these campaigns by Cassini at Saturn in Jan. 2007 and by the New Horizons mission approaching Jupiter in Feb. 2007. The UV auroral emission brightness and distributions have also been compared with estimates of the solar wind conditions near each planet extrapolated from near-Earth measurements, which can be verified by comparison with Cassini and New Horizons in situ data. It has been found that there is a good correlation at both planets between total auroral power and solar wind dynamic pressure, at least for the major solar wind disturbances arriving at each planet. At the same time, the nature of the auroral brightenings differs between Jupiter and Saturn, and the source regions of auroral activity are quite different in the two magnetospheres. In this presentation, the HST and solar wind data and the nature of the correlations will be presented. The physical significance of the correlations will be discussed, based on the much denser set of measurements now available. http://www.bu.edu/csp/PASS/main.html

SM52A-07 

Magnetotail Dynamics in Rapidly Rotating Planets

* Fukazawa, K (fukazawa@nict.go.jp), National Institute of Information and Communications Technology, 4-2-1 Nukui-Kitamachi, Koganei, 184-8795, Japan Ogino, T (ogino@stelab.nagoya-u.ac.jp), Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan Walker, R J (rwalker@igpp.ucla.edu), Institute of Geophysics and Planetary Physics, and Department of Earth and Space Sciences, University of California, Los Angeles, 951567, Los Angeles, CA 90095-1567,

Observations from Cassini and New Horizons as well as magnetohydrodynamic simulations indicate that the two rapidly rotating outer planet magnetospheres at Jupiter and Saturn may be very different. We have used global magnetohydrodynamic simulations to model the interaction between the solar wind and both magnetospheres. At Jupiter we found for northward interplanetary magnetic field (IMF) that a series of magnetic X and O lines were launched tailward with periods between 20 and 56 hours depending on the IMF and solar wind dynamic pressure [Fukazawa et al., J. Geophys. Res., 2006]. Motivated by recent observations of tailward moving structures in Jupiter's distant tail by the New Horizons spacecraft [McComas et al., Magnetospheres of the Outer Planets meeting, 2007] we have developed a new version of the MHD model with a 1500RJ (Jovian radii) long tail to investigate the propagation of these structures and will present results from these simulations. At Saturn we found a magnetotail which frequently is characterized by vortices not found in our Jupiter simulations [Fukazawa et al., Geophys. Res. Lett., 2007]. We also found magnetic X and O regions moving tailward in our Saturn simulations for northward IMF. However, unlike Jupiter they repeated with a period of about 1 hour.

SM52A-08 INVITED 

3D Multi-species Global MHD Studies Of The Solar Wind Interaction With Mars And Saturn's Magnetospheric Plasma Flow With Titan

* Ma, Y (yingjuan@igpp.ucla.edu), IGPP, UCLA, 6877 Slichter Hall, Los Angeles, CA 90095,

This dissertation presented numerical simulation results of the interaction of the solar wind/magnetospheric plasma flow with weakly magnetized/unmagnetized solar system bodies (Mars and Titan) using a multi-species global MHD model. Mars and Titan are both considered as being weakly magnetized/non-magnetized bodies with well-extended atmospheres. Therefore, the solar wind/magnetospheric plasma flow interacts with the corresponding ionosphere/atmosphere systems directly. A 2nd-order Godunov-type, finite-volume, upwind method was used to solve the multi-species MHD equations. The study of the solar wind interaction with Mars started with a three-species MHD model with Cartesian coordinate grid system, which considered protons in the solar wind and the two dominant heavy ions ({O}₂⁺ and {O}⁺) in the ionosphere, separately. More extensive studies were carried out by using an updated 4-species MHD model with a spherical coordinate grid system, which gives a very good altitude resolution and a more realistic ionosphere. The model results are consistent with the Viking observations of the ionospheric ion density and the MGS measured bow shock locations. Using this updated model, we also studied the effects of crustal magnetic field, solar radiation, magnetic field orientation, charge exchange and impact ionization. A three-dimensional 7-species MHD model was used to study the interaction of Titan's ionosphere and Saturn's magnetosphere. The spherical grid system was used in the calculations to get a good resolution in the ionospheric region. The simulation results have been compared with past Voyager measurements and observations of the first three flybys (Ta, Tb and T5) of Titan by Cassini, which agree reasonably well with the observations. The major advantages and limitations of the multi- species MHD models were also discussed in detail.

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