Jupiter and Saturn Magnetospheres II Posters

SPA-Magnetospheric Physics [SM]

SM41A
MC:Hall D Thursday 0800h

Presiding: C Paranicas, Applied Physics Lab; D C Hamilton, University of Maryland

SM41A-1650

Growth-rate analysis of Kronian narrowband emission

* Menietti, J D john-menietti@uiowa.edu, The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States
Ye, S shenyi-ye@uiowa.edu, The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States
Yoon, P H yoon@ipst.umd.edu, University of Maryland, Institute for Physical Science and Technology, College Park, MD 20742, United States
Santolik, O ondrej.santolik@mff.cuni.cz, Charles University, Faculty of Mathematics and Physics, Prague, CZ-18000, Czech Republic
Santolik, O ondrej.santolik@mff.cuni.cz, Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, 14133, Czech Republic
Rymer, A M abigail.rymer@jhuapl.edu, Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20707, United States
Gurnett, D A donald-gurnett@uiowa.edu, The University of Iowa, Department of Physics and Astronomy, Iowa City, IA 52242, United States
Coates, A J ajc@mssl.ucl.ac.uk, University College London, Mullard Space Science Laboratory, Dorking Surrey, RH5 6NT, United Kingdom

Narrowband emission is observed at Saturn centered typically near 5 kHz and 20 kHz and harmonics of each frequency. This emission appears to be in many ways similar to Jovian narrowband emission observed at higher frequencies. We analyze one example of this emission near a probable source region at r = 5.8 R_S, L = 6.9, lat = -23.7°, and local time = 3.3 hours. In situ electron distributions suggest narrowband emission has a source region associated with electrostatic cyclotron and upper hybrid emissions. Linear growth rate calculations indicate that the observed plasma distributions are unstable to the growth of electrostatic harmonic emissions. In addition, it is found that when the local hybrid frequency is close to 2 f_ce or 3 f_ce (f_ce is the electron cyclotron frequency), electromagnetic Z-mode and weak ordinary (O-mode) emission can be directly generated by the cyclotron maser instability. In the presence of density gradients, Z-mode emission can mode-convert into O-mode emission, and this might explain the narrowband emission observed by the Cassini spacecraft.

SM41A-1651

A Sensitivity Study of the Enceladus Torus Chemistry

* Fleshman, B fleshman@nhn.ou.edu, Department of Physics and Astronomy, University of Oklahoma 440 W. Brooks St., Norman, OK 73019, United States
* Fleshman, B fleshman@nhn.ou.edu, Laboratory for Atmospheric and Space Physics Laboratory for Atmospheric and Space Physics, University of Colorado Campus Box 392, Boulder, CO 80309-0392, United States
Delamere, P delamere@lasp.colorado.edu, Laboratory for Atmospheric and Space Physics Laboratory for Atmospheric and Space Physics, University of Colorado Campus Box 392, Boulder, CO 80309-0392, United States
Bagenal, F bagenal@lasp.colorado.edu, Laboratory for Atmospheric and Space Physics Laboratory for Atmospheric and Space Physics, University of Colorado Campus Box 392, Boulder, CO 80309-0392, United States

We have developed a homogeneous cubic centimeter chemistry model to investigate the Enceladus torus. Electron impact dissociation/ionization, electron recombination, charge exchange (including dissociative exchanges), and photodissociation/photoionization are included. The mass source is neutral H₂O, and energy is input from pickup of ionized neutrals by the magnetosphere. Mass and energy losses are due to ion radial diffusion, radiation, and escaping hot neutrals produced by charge exchange and recombination. In addition, we have performed a sensitivity study involving the following: hot electron (1) temperature and (2) population fraction (n_eh/n_ec), (3) ion radial diffusion timescale, (4) neutral source rate, and (5) dilution of equatorial protons caused by the ambipolar potential. Parameter combinations are chosen so that model output most closely matches Cassini data for: (1) electron density [RPWS, Persoon et al. (2006)], (2) core electron temperature [CAPS-ELS, Lewis et al. (2008)], and (3) on the mixing ratio of water group ions to protons (W⁺/H⁺) [CAPS, Williams (2008)] . Note that this set of constraints is arbitrary. Parameter ranges consistent with these constraints will be presented.

http://www.nhn.ou.edu/~fleshman/Research/enceladus_08.pdf

SM41A-1652

Preliminary Model of Jupiter's Plasma Sheet

* Desroche, M desroche@colorado.edu, University of Colorado, Laboratory of Atmospheric and Space Physics 392 UCB, Boulder, CO 80303, United States
Bagenal, F bagenal@colorado.edu, University of Colorado, Laboratory of Atmospheric and Space Physics 392 UCB, Boulder, CO 80303, United States
Paterson, W R bill.paterson@hamptonu.edu, Hampton University, Center for Atmospheric Sciences, Hampton, VA 23668, United States

Our objective is to develop an empirical model of the plasma density, flow, temperature and composition in the middle/outer regions of the magnetosphere (10-40 R_j) in order to elucidate processes of plasma heating and transport in this region. We begin by combining ion plasma moments computed from Galileo's plasma instrument with the Connerney magnetic field model to extrapolate in situ measurements of primary plasma properties along the magnetic field. Using functional fits to the Galileo data of (based on Frank et al. 2002), we have begun to develop maps of ion and electron densities with various assumptions of composition and thermal anisotropy. We also present order of magnitude calculations for Alfven speed and plasma beta. With the inclusion of data sets from other Galileo orbits, as well as from Voyagers and New Horizons spacecraft, we aim to map the plasma sheet structure as functions of radial distance, latitude, local time and epoch, which will constrain models of plasma transport in the middle magnetosphere.