Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53c..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P53C-02
Physics
[2756] Magnetospheric Physics / Planetary Magnetospheres, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [5719] Planetary Sciences: Fluid Planets / Interactions With Particles And Fields, [5744] Planetary Sciences: Fluid Planets / Orbital And Rotational Dynamics
Scientific paper
Saturn has three types of radio emissions that display a well-defined rotational modulation. They are: (1) Saturn kilometric radiation (SKR), which is an intense radio emission at frequencies from about 50 to 500 kHz that is believed to be produced by precipitating auroral electrons via the cyclotron maser mechanism; (2) auroral hiss, which is a broadband whistler-mode emission at frequencies below about 100 Hz that is believed to be produced by upgoing field-aligned electron beams associated with the auroral current circuit; and (3) narrowband 5 kHz emissions, which are believed to be generated by mode conversion from the Z-mode waves in the inner region of the magnetosphere. The SKR is known to originate from a clock-like source primarily in the late local morning region of the magnetosphere, and the auroral hiss originates from a high-latitude rotating beam source that sweeps through all local times. The narrowband 5 kHz emissions tend to occur in distinct "storms" lasting several days, and can display both clock-like and rotating beam characteristics. All three types of emissions have two distinct modulation periods that slowly vary in time, currently at about 10.6 and 10.8 hours. Both the SKR and the auroral hiss have a clear north-south asymmetry, with the 10.6-hour period originating from the northern auroral region, and the 10.8-hour period originating from the southern auroral region. The narrowband 5 kHz emissions display both 10.6 and 10.8 hour periods in both hemispheres, possibly because the north-south location of the source of these emissions cannot be adequately resolved. These complex temporal and latitudinal effects almost certainly play an important role in the coupling of angular momentum from the interior of the planet to the magnetosphere. Factors that might be involved include seasonal differences in the conductivity of the upper atmosphere in the two hemispheres, latitudinal variations in upper atmospheric zonal winds, or possibly short-term secular variations in Saturn's internally generated magnetic field.
Groene J.
Gurnett Donald A.
Kurth Willaim S.
Persoon Ann M.
Wang Ziqiang
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