Cassini and Wind stereoscopic observations of Jovian nonthermal radio emissions: Measurement of beam widths

During two intervals in 1999, simultaneous observations of Jupiter's decame tric and hectometric radio emissions were made with the Cassini radio and p lasma wave instrument (RPWS) and the radio and plasma wave instrument (WAVE S) on the Wind spacecraft in Earth orbit. During January the Jovian longitu de difference between the two spacecraft was about 5 degrees, whereas for t he August-September Earth flyby of Cassini, the angle ranged from 0 degrees to about 2.5 degrees (the Jovicentric latitudinal difference was <0.3 degr ees during both intervals). With these separations the instantaneous widths of the walls of the hollow conical radiation beams of some of the decametr ic area were measured by cross correlating dynamic spectra. The results sug gest that the typical width is approximately 1.5 degrees +/- 0.5 degrees. T he conical beams seem to move at Io's revolution rate for Io-controlled arc s. Additionally, some of the nonarc hectometric wavelength emissions show s ome properties of both wide and very narrow beam widths.