Solar Wind modulation of Saturn's radio clock

Details Solar Wind modulation of Saturn's radio clock Solar Wind modulation of Saturn's radio clock

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p31a0193l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P31A-0193

Physics

5706 Aurorae, 5737 Magnetospheres (2756), 6275 Saturn, 6939 Magnetospheric Physics (2700)

Scientific paper

The internal rotation rates of the giant planets can be estimated by cloud motions, but that is not very precise because absolute wind speeds are not known a priori and depend on latitude. Periodicities in the radio emissions, thought to be tied to the internal planetary magnetic field, are instead used. At Saturn, in spite of an apparently axisymmetric magnetic field, kilometer-wavelength emission arising from auroral sources is modulated at a period initially identified as 10h 39m 24s ±7s, and this has been adopted as Saturn's rotation period. Subsequent observations, however, revealed that this period varies by ±6 min on a timescale of several months to years. Here we report measurements of the periodicity of the kilometric radiation that reveal that the period varies systematically by ±1 percent with a characteristic timescale of 20-30 days. We demonstrate that these fluctuations are correlated with those of the solar wind speed at Saturn. This provides evidence that Saturn's radio clock is controlled, at least in part, by conditions external to the planet's magnetosphere. No correlation is found with the solar wind density, dynamic pressure or magnetic field, therefore the solar wind speed plays a special role. We also demonstrate that the long term fluctuations are simply an average of the short term ones, and therefore the long term variations are probably also driven by changes in the solar wind.

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