A proper understanding of the effects of turbulence on the diffusion and drift of cosmic-rays in
the heliosphere is imperative for a better understanding of cosmic-ray modulation. This study
presents an ab initio model for cosmic-ray modulation, incorporating for the first time the results
yielded by a two-component turbulence transport model. The latter model is solved for
solar minimum heliospheric conditions, utilizing boundary values chosen in such a way that
the results of this model are in fair to good agreement with spacecraft observations of turbulence
quantities, not only in the ecliptic plane, but also along the out-of-ecliptic trajectory of the
Ulysses spacecraft. These results are employed as inputs for modelled slab and 2D turbulence
energy spectra, which in turn are used as inputs for parallel mean free paths based on those
derived from quasi-linear theory, and perpendicularmean free paths from extended nonlinear
guiding center theory. The modelled 2D spectrum is chosen based on physical considerations,
with a drop-off at the very lowest wavenumbers commencing at the 2D outerscale. There currently
exist no models or observations for this quantity, and it is the only free parameter in this
study. The use of such a spectrum yields a non-divergent 2D ultrascale, which is used as an
input for the reduction terms proposed to model the effects of turbulence on cosmic-ray drifts.
The resulting diffusion and drift coefficients are applied to the study of galactic cosmic-ray
protons, electrons, antiprotons, and positrons using a three-dimensional, steady-state numerical
cosmic-ray modulation code. The magnitude and spatial dependence of the 2D outerscale
is demonstrated to have a significant effect on computed cosmic-ray intensities. A form for the
2D outerscale was found that resulted in computed cosmic-ray intensities, for all species considered,
in reasonable agreement with multiple spacecraft observations. Computed galactic
electron intensities are shown to be particularly sensitive to choices of parameters pertaining
to the dissipation range of the slab turbulence spectrum, and certain models for the onset
wavenumber of the dissipation range could be eliminated in this study. / Thesis (PhD (Physics))--North-West University, Potchefstroom Campus, 2013
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/8735 |
| Date | January 2012 |
| Creators | Engelbrecht, Nicholas Eugéne |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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