The transport of cosmic rays in the heliosphere is studied by making use of a newly developed
modulation model. This model employes stochastic differential equations to numerically solve
the relevant transport equation, making use of this approach’s numerical advantages as well
as the opportunity to extract additional information regarding cosmic ray transport and the
processes responsible for it. The propagation times and energy losses of galactic electrons
and protons are calculated for different drift cycles. It is confirmed that protons and electrons
lose the same amount of rigidity when they experience the same transport processes. These
particles spend more time in the heliosphere, and also lose more energy, in the drift cycle
where they drift towards Earth mainly along the heliospheric current sheet. The propagation
times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric
tilt angles and it is found that current sheet drift becomes less effective with increasing solar
activity. Comparing calculated propagation times of Jovian electrons with observations, the
transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth
are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton
to anti-proton ratio at Earth and comparing the results to recent PAMELA observations.
A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation
model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using
this model, it is shown that cosmic ray modulation persists beyond the heliopause. The
level of modulation in this region is found to exhibit solar cycle related changes and, more
importantly, is independent of the magnitude of the individual diffusion coefficients, but is
rather determined by the ratio of parallel to perpendicular diffusion. / PhD (Space 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:10394/10217 |
| Date | January 2013 |
| Creators | Strauss, Roelf du Toit |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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