Correlations Between Narrowband Radio Emissions and Transient Rotating Plasma Clouds in Saturn's Magnetosphere

Details Correlations Between Narrowband Radio Emissions and Transient Rotating Plasma Clouds in Saturn's Magnetosphere Correlations Between Narrowband Radio Emissions and Transient Rotating Plasma Clouds in Saturn's Magnetosphere

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p43a1016w&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P43A-1016

Other

2756 Planetary Magnetospheres (5443, 5737, 6033), 6275 Saturn, 6984 Waves In Plasma (7867)

Scientific paper

The RPWS (Radio and Plasma Wave Science) instrument onboard the Cassini spacecraft has frequently detected a series of narrowband electromagnetic emissions from the inner magnetosphere of Saturn from May 2005 to July 2007. Frequency-time spectrograms show that the strongest narrowband emissions tend to occur at frequencies near 5 kHz with bandwidths of about 2 to 3 kHz. Other apparently associated bands also occur at higher frequencies, sometimes as high as 30 kHz. Analysis of all the events detected over a two-year period shows that the emissions tend to be observed more frequently on the night side of the planet, as well as at latitudes away from the equator. The longitude of the Sun using a longitude system recently developed by Kurth et al. organizes the narrowband radio emissions better than the longitude of the spacecraft, indicating that the modulation of the radio emissions is acting more like a flashing light than a rotating beacon. The narrowband radio emissions are believed to be produced by mode conversion from electrostatic waves near the upper hybrid frequency at about L ~ 7 to 8 and latitudes of ±30 degrees. Our studies show that the transient hot plasma clouds rotating around the planet inside the orbit of Titan, may be the source for narrowband radio emissions for three reasons. First, the hot plasma clouds are produced by ENA (energetic neutral atom) emissions, which are detected by MIMI (INCA), through charge exchange. ENA images of Saturn's magnetosphere show that the hot plasma clouds rotate around the planet in the region from 7 to 8 RS, and this agrees with the source location required by the above mode conversion model. Second, ENA emissions tend to show stronger intensities on the night side of Saturn, consistent with the narrowband radio emissions that are also observed more frequently on the night side. Third, the narrowband radio emissions and ENA emissions are well correlated in time. In most cases (20 out of 30), narrowband radio emissions are accompanied by clear ENA emissions. Of the remaining cases, 8 narrowband radio emissions fall in the gaps of ENA data, and the correlations between them can not be verified.

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