HR: 1340h
AN: P43A-1017    [Abstracts]
TI: Source Location of Narrowband Radio Emission Detected at Saturn
AU: * Ye, S
EM: shengyi-ye@uiowa.edu
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Gurnett, D A
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Fischer, G
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Menietti, J D
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Kurth, W S
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Wang, Z
AF: University of Iowa, Dept. of Physics and Astronomy, Iowa City, IA 52242, United States
AU: Cecconi, B
AF: Observatoire de Paris, LESIA, Meudon, 92195, France
AU: Zarka, P
AF: Observatoire de Paris, LESIA, Meudon, 92195, France
AU: Rymer, A
AF: Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, United States
AU: Young, D T
AF: Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228, United States
AU: Coates, A J
AF: Mullard Space Science Laboratory, University College London, Surrey, RH5 6NT, United Kingdom
AB: Since Cassini's arrival at Saturn in 2004, the Radio and Plasma Wave Science (RPWS) instrument has detected a series of narrowband radio emissions in Saturn's magnetosphere. It is believed that these narrowband emissions are first excited as electrostatic waves by electrons when the matching condition f_uh = (n+1/2)f_ce is met, where f_uh is the upper hybrid frequency and f_ce is the electron cyclotron frequency. These upper hybrid waves can mode convert to electromagnetic L-O waves in the presence of density gradients. We determined the polarization of the narrowband emissions and found it to be consistent with the prediction of linear mode conversion theory. To model the source region of narrowband emissions, we numerically calculated the locations where the matching condition is met in a meridian plane, using a scale height electron density model [Persoon et al., 2006] and a dipole magnetic field model. For the 5 kHz narrowband emission, the matching condition f_uh = 3/2 f_ce is met at a radial distance of 5.6 R_S and latitude of 32.6 degrees. For the 20 kHz emission, f_uh = 3/2f_ce is met at 3.3 R_S and 15.7 degrees latitude. In several selected events, Cassini went through the source region of narrowband emissions, as indicated by a strong electrostatic band preceding the radio emission. The coordinates of Cassini when the source of narrowband emissions are encountered closely match that predicted by the model. For these encounters with the narrowband emission source, we investigate the electron distribution functions obtained from the electron spectrometer (ELS) onboard Cassini, and perform an initial wave growth analysis for the electrostatic waves. For the electromagnetic radio component of narrowband emission, we employ a polarization reversal technique to determine the source locations. While the Cassini spacecraft is rotating, the apparent polarization of the radio emission measured by RPWS switches its rotation sense when the source goes through the antenna plane. By finding the intersection of the plane which contains the source with a ring of possible source locations predicted by our model, we can determine the longitudinal coordinate of the source.
DE: 6275 Saturn
DE: 6984 Waves in plasma (7867)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting