Marius S. Potgieter

The combined modulation of Jovian and Galactic electrons in the heliosphere

The propagation and modulation of electrons in the heliosphere play a significant role in improving our understanding and assessment of the competing processes of solar modulation. An in-house developed, full three-dimensional numerical model is used to study the total modulation of Jovian and Galactic electrons from 1 MeV to 50 GeV, and from the heliopause into the heliosphere, up to Jupiter and the Earth. For this purpose the Jovian electron source and the heliopause (a very local interstellar) electron spectrum must be specified in the model. The latter can be computed with confidence since Voyager 1 already crossed the heliopause returning the measured spectra from this very local interstellar region. nModeling results are compared with Voyager 1 observations in the outer heliosphere, including the heliosheath, as well as observations at or near the Earth, in particular the 2009 spectrum from the PAMELA space mission, ISSE 3 and from Ulysses for 1991 and 1992. Making use of the observations at Earth and the source function for the Jovian electrons, the energy range over which the Jovian electrons dominate the Galactic electrons can be determined. The intensity of Galactic electrons at Earth is computed subsequently. This gives a conclusive finding about the energy range where the Jovian particles dominate the Galactic electrons and determining the absolute intensity value that the Galactic particles can have at the Earth. The highest differential intensity for the Galactic electrons at the Earth for kinetic energy of 1 MeV is ~20 m-2 s-1 sr-1 MeV-1, whereas for Jovian electrons it is ~400 m-2 s-1 sr-1 MeV-1.