Session 2: Solar, Planetary and Space Physics

Title:  Periodic signals in Ulysses' energetic particle events upstream and downstream from the Jovian bow shock.
Author(s):  P.K. Marhavilas, G.C. Anagnostopoulos, E.T. Sarris (Oral)

We present results from a statistical analysis of Jovian upstream energetic particle ion and electron events, observed by the HI-SCALE instrument onboard Ulysses, during the inbound and outbound trajectory of the spacecraft. A harmonic analysis on the intensity time series of 192 distinct 61-77 KeV upstream ion events, suggests a modulation with a period of ~40 min or ~15-20 min in 48% of the total number of the events, at the significance level of P=0.05. In some cases the periodicity is not significant in the ion intensities, while it is significant in the ion anisotropy and/or spectral data. Our analysis shows that the above periodic modulation was more frequently observed on the out of the ecliptic trajectory (67 events), than on the ecliptic trajectory (26 events). A ~40/ 15-20 min periodicity was also found in energetic ion and electron events in the  magnetosheath. The results from the statistical analysis of HI-SCALE measurements, are consistent with a magnetospheric source for the majority of the upstream events. The statistical results are also consistent with preferential leakage of energetic ions from the south high latitude Jovian magnetosphere.