The combined modulation of Jovian and Galactic electrons in the heliosphere
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Date
2017Author
Potgieter, Marius S.
Nndanganeni, Rendani R.
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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. Modeling 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