Journal article
Source locations of narrowband radio emissions detected at Saturn
Journal of geophysical research. Space physics, Vol.114(A6), pp.A06219-n/a
06/2009
DOI: 10.1029/2008JA013855
Abstract
Since Cassini's arrival at Saturn in 2004, the Radio and Plasma Wave Science instrument has detected numerous narrowband (NB) radio emission events. These emissions, mostly detected around 5 and 20 kHz, usually occur periodically for several days after intensifications of Saturn kilometric radiation. We present calculations based on an electron density profile of Saturn's plasma torus and a dipole magnetic field model showing that the NB emissions originate from the northern and southern edges of Saturn's plasma torus at L shells similar to 8 to 10 for 5-kHz NB and L similar to 4 to 7 for 20-kHz NB. In many cases, Cassini passes through the source region of the 20-kHz NB, as indicated by intense electrostatic upper hybrid (ESUH) waves in close proximity to electromagnetic emissions on spectrograms. The positions of the spacecraft when intense ESUH waves are observed agree with the model predictions of the NB source locations. Source locations determined by goniopolarimetric (also known as direction-finding) analysis of the NB emissions also support the above results, although sometimes the directions of arrival point toward the region interior to Saturn's plasma torus. A polarization reversal technique is applied to localize the NB emissions observed during spacecraft rotation, on the basis of the fact that the source is within the antenna plane when the apparent circular polarization degree switches sign. The NB emissions are found to be L-O mode polarized, which is consistent with the prediction of linear/nonlinear mode conversion theory. It is also found that sometimes right-hand polarized NB emissions are generated at second harmonic frequencies of the 20-kHz NB; in which case, wave-wave interactions between oppositely propagating ESUH waves may play an important role in the mode conversion process.
Details
- Title: Subtitle
- Source locations of narrowband radio emissions detected at Saturn
- Creators
- Sheng-Yi Ye - Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USAD. A. Gurnett - University of IowaG. Fischer - University of IowaB. Cecconi - Observatoire de ParisJ. D. Menietti - University of IowaW. S. Kurth - University of IowaZ. Wang - University of IowaG. B. Hospodarsky - University of IowaP. Zarka - Observatoire de ParisA. Lecacheux - Observatoire de Paris
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.114(A6), pp.A06219-n/a
- DOI
- 10.1029/2008JA013855
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Publisher
- Amer Geophysical Union
- Number of pages
- 21
- Grant note
- 1279973 / Jet Propulsion Laboratory; National Aeronautics & Space Administration (NASA) NASA; National Aeronautics & Space Administration (NASA)
- Language
- English
- Date published
- 06/2009
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455260402771
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