dc.contributor.advisor | Ferreira, S.E.S. | |
dc.contributor.advisor | Manuel, R. | |
dc.contributor.advisor | Potgieter, M.S. | |
dc.contributor.author | Mohlolo, Selwana Timothy | |
dc.date.accessioned | 2017-10-31T10:18:21Z | |
dc.date.available | 2017-10-31T10:18:21Z | |
dc.date.issued | 2016 | |
dc.identifier.uri | http://hdl.handle.net/10394/25974 | |
dc.description | MSc (Space Physics), North-West University, Potchefstroom Campus, 2017 | en_US |
dc.description.abstract | This work studied the modulation of galactic cosmic rays in the heliosphere by using a well-established,
time dependent numerical modulation model to calculate cosmic ray transport
inside the heliosphere over a solar cycle. Results were compared to observations from the
Voyager 1 and 2 spacecraft. It was shown that, when using the modified compound approach
of Manuel et al. [2014] to scale the transport coefficients over a solar cycle, the model resulted
in compatibility with spacecraft observations on a global scale. However, for certain periods,
e.g. 1985 - 1990 and 1992 - 2001, the model did not agree with observations. For instance, for
the period 1985 - 1990, the Voyager 1 spacecraft observed a plateau-like intensity profile while
the model computed a peak-like intensity profile along the Voyager 1 trajectory. Voyager 2
on the other hand measured a peak-like intensity profile as expected from a traditional drift
description of cosmic ray intensities around solar minimum. It was shown that, for this period,
the Voyager 1 spacecraft was above the heliospheric current sheet region while Voyager 2 was
inside the heliospheric current sheet region close to the equatorial region. It was shown that the
time-dependent function that scales drifts up or down depending on the level of solar activity
over a solar cycle, resulted in the peak-like intensity profile compatible with Voyager 2 observations
but not Voyager 1 observations. It was proposed that this time-dependent function
has a latitude dependence with different values inside and outside of the heliospheric current
sheet, i.e. a different dependence above compared to in the heliospheric current sheet region.
This improved compatibility between the model and Voyager 1 observations. However, the full
implementation of such an additional spatial dependence in the 2D model is beyond the scope
of this study. For the period 1992 - 2001, it was shown that the tilt angle increases much faster
towards solar maximum than the corresponding decrease in observed cosmic ray intensities.
This resulted in the model computing intensities decreasing faster than the observed intensities
as a function of increasing solar activity and therefore causing incompatibility between
the model and the observations. It was shown for this period that modifying the tilt angle by
using an averaged tilt angle resulted in improved compatibility with observations. | en_US |
dc.language.iso | en | en_US |
dc.publisher | North-West University (South Africa) | en_US |
dc.subject | Heliosfeer | en_US |
dc.subject | Kosmiese strale | en_US |
dc.subject | Sonsiklus | en_US |
dc.subject | Modulasie | en_US |
dc.subject | Sonaktiwiteit | en_US |
dc.subject | Deeltjie dryf | en_US |
dc.subject | Heliosphere | en_US |
dc.subject | Cosmic rays | en_US |
dc.subject | Solar cycle | en_US |
dc.subject | Modulation | en_US |
dc.subject | Solar activity | en_US |
dc.subject | Particle drifts | en_US |
dc.title | The modulation of galactic cosmic rays over a solar cycle | en_US |
dc.type | Thesis | en_US |
dc.description.thesistype | Masters | en_US |
dc.contributor.researchID | 10060014 - Potgieter, Marthinus Steenkamp (Supervisor) | |
dc.contributor.researchID | 21245274 - Manuel, Rex (Supervisor) | |
dc.contributor.researchID | 10713158 - Ferreira, Stephanus Esaias Salomon (Supervisor) | |