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The Uranian kilometric emissions detected by the Voyager 2 Planetary Radio Astronomy (PRA) experiment during the January 1986 encounter comprise two distinct types of emission: bursts and continuum. The bursts have been treated by Evans et al. (this issue). This paper considers the continuum emissions. The continuum emissions comprised four components: equatorial emissions, anomaly emissions, strong nightside emissions, and weak nightside emissoins. These components are associated with different sources. In all cases the electron gyrofrequency and the extraordinary mode in the various source regions define the observed wave frequencies and polarizations. The equatorial emissions appeared most prominently during the days before closest approach and extended from 40 kHz or below to approximately 120 kHz. These emissions originate near the offset tilted dipole (OTD) magnetic equator. They are beamed perpendicularly to the local field lines. The anomaly emissions were seen about 12 hours before closest approach and extended to approximately 250 kHz. They originate within the ''Q3 dayside polar anomaly'' described by Connerney et al. (this issue). The strong and weak nightside emissions were seen near the and after closest approach and extended from 40 to 865 kHz. These emissions are accurately modeled by sources in the OTD magnetic field. The strong nightside source is located on the nightside L-5 shell, and the emission is beamed into a solid cone of half-angle 10¿ to 30¿, centered about the direction of the local magnetic field. The cone narrows monotonically with increasing frequency. The weak nightside source is located on high nightside L shells (L>100), and the emission is beamed perpendicularly to the local magnetic field. The weak nightside emission may be associated with bursts. Miranda, orbiting Uranus in nearly a 2:1 ratio to the 17.24-hour PRA radio rotation period, may play a role in Uranian kilometric emissions. A coincidence between Miranda's phase and strong radio emission at 20.4 kHz, just after closest approach, suggests intense dynamic activity on the Miranda L shell. ¿ American Geophysical Union 1987 |
