Simultaneous observations of Jovian quasi‐periodic radio emissions by the Galileo and Cassini spacecraft

The gravity‐assist flyby by Cassini of Jupiter on 30 December 2000 and the extended Galileo orbital mission provided a unique opportunity to obtain simultaneous measurements with two spacecraft of many Jovian plasma wave and radio emissions. One of these emissions is Jovian type III radio emissions, also known as Jovian quasi‐periodic (QP) emissions. The simultaneous observations of the QP emissions show very similar characteristics, even when the two spacecraft are separated by large distances and located at very different local times (LT). These similarities suggest that this emission is beamed in a strobe light like manner (over a large angular range) and not like a search light rotating with Jupiter's magnetic field, as many other Jovian radio emissions are. The initial source of the QP bursts is likely located near Jupiter. As the emissions propagate through the magnetosphere, the QP bursts appear as enhancements of the trapped continuum. At the magnetosheath the higher density plasma disperses the lower frequency component of the bursts, producing the characteristic “type III like” spectral shape.