Time-dependent 3D modulation of Jovian electrons

Comparison with Ulysses/KET observations

Institut für Theoretische Physik IV, Weltraum- und Astrophysik, Ruhr-Universität, Bochum, Germany e-mail: dennie@tp4.rub.de

Received: 17 August 2005
Accepted: 27 October 2005

Abstract

We report on the modelling of the time-dependent transport of a few MeV electrons in the heliosphere. These low-energetic electrons, observed with the Kiel Electron Telescope (KET) on board the Ulysses spacecraft, are for the first time simulated over a complete solar activity cycle on the basis of a time-dependent three-dimensional modulation model. It is demonstrated that the solar activity has an effect especially at high heliographic latitudes being observed by Ulysses. The findings of the Ulysses mission lasting almost 15 years now provide a substantial data base for this study. Both galactic cosmic rays and the Jovian electron source are considered for the simulation of the electron fluxes within the heliosphere. Originating from these simulations two models for the time-dependent solar wind expansion are suggested, formulated and tested. Both characterise the varying velocity field of the solar wind over a solar cycle. A time-dependent anisotropic diffusion tensor was also tested in order to figure out from KET observations the variation of the release rate of low-energetic electrons from the Jovian magnetosphere.