MeV to GeV electron propagation and modulation: Results of the KET-telescope onboard Ulysses

Abstract

The KET instrument onboard Ulysses is continuously monitoring the flux of MeV to GeV electrons. I summarize here the main results obtained with data from the ∼ 7 MeV and > 300 MeV electron KET channels, collected from launch up to the end of 1995 after completion of the Ulysses prime mission. Regarding low energy electrons, the stress is put on the study of Jovian electron events, which were used to derive the values of the three diagonal diffusion coefficients in interplanetary space. The ∼ 7 MeV parallel mean free path is found to be large (∼ 1 AU). The radial diffusion coefficient perpendicular to the average magnetic field is ∼ 0.5 % of that along the field, while the ratio of the polar diffusion coefficient to the radial one is less than unity. Regarding the high energy electrons, the KET data show that the flux at ∼ 300 MeV has been constant during the full period, whereas the maximum recovery, at ∼ 700 MeV, was by a factor of ∼ 5. Regarding the comparison with proton modulation, the e/p ratio strongly decreased in 1991, which is tentatively correlated with the reversal of the sun's magnetic field. During the fast latitude scan of Ulysses, under solar minimum conditions, no significant latitude dependent feature is found for Galactic electrons, implying a much smaller, if any, latitudinal gradient compared to that of protons, which is already small.