Evidence provided by Galileo of ultra low frequency waves within Jupiter's middle magnetosphere

The Voyager and Ulysses spacecraft measurements from the dayside of Jupiter's middle magnetosphere provided evidence for ultra low frequency waves in the magnetometer data, in particular waves of periods 10 - 20 minutes. Galileo is the first orbiter mission around Jupiter and the,first to extensively study the nightside magnetosphere. Similar waves are discernible when Galileo passed through the equatorial current sheet with very few features being noticed outside of the current sheet regions. An overview of the data shows that only 12% of crossings do not have any wave signatures in any component of magnetic field in the 10 - 20 minute period regime. The majority of these waves are found in the perpendicular field component. These waves are thus prevalent over the nightside magnetosphere and when combined along with the earlier work on the dayside seems to suggest that these ultra low frequency waves are a global phenomenon.