EVIDENCE FOR RESONANT MODE-COUPLING IN SATURNS MAGNETOSPHERE

Ultralow-frequency (ULF) pulsations are an important class of phenomen a characterizing the dynamics of the terrestrial magnetosphere and are usually interpreted as standing magnetohydrodynamic waves in the magn etospheric plasma of planet Earth. Spacecraft observations indicate th at the Hermean and Jovian magnetospheres also support such eigenoscill ations. Whether ULF waves exist in the magnetosphere of the planet Sat urn is the topic of this work. On the basis of a simple plasma mass di stribution model, periods of Kronian eigenoscillations are estimated. Values comparable to the planetary rotation period are found, which ma kes the existence of standing waves improbable. Despite this significa nt difference in Earth's magnetosphere it is shown that this does not inhibit the resonant coupling between fast mode type magnetopause surf ace waves and local propagating Alfven modes. Against this background we examine a pattern in the magnetic field data recorded by Voyager 1 during its encounter with Saturn. The analysis of the pattern and a mo deled satellite crossing give indications that resonant mode coupling was detected.