Bonn 2010 – wissenschaftliches Programm
EP 3.11: Poster
Montag, 15. März 2010, 17:45–19:00, AKM Foyer
Current-sheet driven spectral modulation of MeV electrons in the Jovian magnetosphere: Ulysses observations — •Andreas Kopp, Phillip Dunzlaff, and Bernd Heber — IEAP, Christian-Albrechts-Universität zu Kiel, 24118 Kiel
The dynamics of the Jovian magnetosphere is dominated by the planet's fast rotation with a period of about 10h. This periodicity can in particular be seen in the temporal variation of the spectral index of energetic particles. Derived from Pioneer observations, three models were developed to explain this phenomenon, the most prominent of which is the so-called Jovian clock model. Based on the observation of only a 10h periodicity being present in the data, this model predicts that this periodicity is caused only by temporal, but not by spatial variations, i.e. the observations become independent of the spacecraft's position. In order to investigate the origin of this 10h periodicity, we re-investigated data of the KET and HET instruments aboard Ulysses during the spacecraft's Jupiter flyby in February 1992. In contrast to former analyses, we could find by means of a Lomb-Scargle analysis additionally a small, but significant 5h periodicity, suggesting a connection with the current sheet. A closer analysis revealed the signal to be caused by a 10h variation due to the rotation of the magnetosphere being interrupted by crossings of the current sheet. The peaks of this 10h variation can be explained by crossings of the dipole plane with the spacecraft's trajectory. We conclude, thus, that the 10h periodicity can be explained by a simple model of the rotating, tilted dipole eld and the resulting up and down motion of the current sheet.