HR: 1340h
AN: P43A-1019    [Abstracts]
TI: Energy Flow in Saturn's Ion Cyclotron Wave Belt
AU: * Leisner, J S
EM: jleisner@ess.ucla.edu
AF: Institute of Geophysics and Planetary Physics, Slichter Hall University of California, Los Angeles, Los Angeles, CA 90095, United States
AU: Russell, C T
AF: Institute of Geophysics and Planetary Physics, Slichter Hall University of California, Los Angeles, Los Angeles, CA 90095, United States
AU: Dougherty, M K
AF: Space and Atmospheric Physics, The Blackett Laboratory, Imperial College London, Prince Consort Road, South Kensington, London, SW7 2BW, United Kingdom
AU: Persoon, A M
AF: Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, United States
AU: Blanco-Cano, X
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria, Coyoacan, DF 04510, Mexico
AU: McAndrews, H J
AF: Los Alamos National Laboratory, MS D466 P.O. Box 1663, Los Alamos, NM 87545, United States
AU: Thomsen, M F
AF: Los Alamos National Laboratory, MS D466 P.O. Box 1663, Los Alamos, NM 87545, United States
AU: Strangeway, R J
AF: Institute of Geophysics and Planetary Physics, Slichter Hall University of California, Los Angeles, Los Angeles, CA 90095, United States
AB: When molecules in Saturn's water-group neutral cloud are ionized, they are accelerated by the electric field associated with the motion of the magnetospheric plasma. This acceleration brings the pick-up ions to the bulk plasma speed and gives them free energy that leads to the growth of ion cyclotron waves. Ion cyclotron waves propagating along the magnetic field have been observed near the equatorial plane on almost all of Cassini's orbits through the inner magnetosphere. On near-equatorial orbits, these waves are observed to peak below the gyrofrequencies of water-group (O, OH, H₂O) and molecular oxygen (O₂) ions. On inclined orbits, the velocity of the spacecraft along the waves' direction of propagation produced Doppler shifts in the wave frequency. Using this shift, we calculate the phase velocity of the waves through the wave belt. We find that near the magnetic equator, the waves are propagating both parallel and anti-parallel to the magnetic field and have phase velocities of 40-50 km/s, one-half to one-third of the local Alfven speed. Beyond +/- 0.04 Rs of the magnetic equator, the water-group waves are propagating away from that plane and increasing in power until about +/- 0.25 Rs. Then they quickly damp. The wave power profile is similar for molecular oxygen waves, except these waves are about one-tenth as strong. Beyond +/- 0.3 Rs of the magnetic equator the water-group waves are absent, but the molecular oxygen waves persist until higher latitudes, although with low power. We discuss the energy carried by these waves, considering both ion species and where the background plasma gains energy from their absorption.
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 2772 Plasma waves and instabilities (2471)
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting