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On January 24, 1986, during the inbound trajectory to Uranus, the planetary radio astronomy instrument on board Voyager 2 detected left-hand polarized emission for several hours at frequencies near 200 kHz. Unlike the dominant source observed on the nightside of the planet, only a single episode of this inbound emission was seen, and the emission was extremely weak. Generating less than 500 kW, it is probably the weakest freely propagating planetary radio emission thus far observed by Voyager. We associate this weak emission with a source region in the vicinity of Uranus' north (dayside) magnetic pole, where magnetic field lines point approximately in the direction of the spacecraft when the emission is observed. Therefore the wave normal angle relative to B is probably less than 90¿ in the generation region. We conclude that direct wave generation in the magnetoionic ordinary mode is most likely. The source location for this emission is consistent with a region magnetically conjugate to the dominant nightside source, which is located in the vicinity of the south magnetic pole. The ordinary mode emission is discussed in the context of the electron cyclotron maser mechanism. ¿ American Geophysical Union 1987 |