Evidence provided by Galileo of ultra low frequency waves within Jupiter'smiddle 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. Gali leo is the first orbiter mission around Jupiter and the,first to extensivel y study the nightside magnetosphere. Similar waves are discernible when Gal ileo passed through the equatorial current sheet with very few features bei ng noticed outside of the current sheet regions. An overview of the data sh ows that only 12% of crossings do not have any wave signatures in any compo nent of magnetic field in the 10 - 20 minute period regime. The majority of these waves are found in the perpendicular field component. These waves ar e thus prevalent over the nightside magnetosphere and when combined along w ith the earlier work on the dayside seems to suggest that these ultra low f requency waves are a global phenomenon.