Browsing Faculty of Natural and Agricultural Sciences by Author "10060014 - Potgieter, Marthinus Steenkamp"
Now showing items 1-20 of 96
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Acceleration of galactic electrons at the solar wind termination shock and Voyager 1 observations
Potgieter, Marius S.; Prinsloo, P. Lourens; Strauss, R. Du Toit (PoS, 2017)Diffusive shock acceleration (DSA) , as an acceleration process for G alactic electrons at the solar wind termination shock (TS) , is investigated with a comprehensive numerical model which ... -
Are anomalous cosmic rays the main contribution to the low-energy galactic cosmic ray spectrum?
Scherer, K.; Ferreira, S.E.S.; Büsching, I.; Potgieter, M.S.; Fichtner, H. (IOP Publishing, 2008)While the high-energy part of the Galactic cosmic ray spectrum is well observed, its nature at energies below about 1 GeV nucleon-1 is still not known well. Recent in situ measurements made with the Voyager 1 spacecraft in ... -
Challenges to cosmic ray modeling: from beyond the solar wind termination shock
Potgieter, M.S. (Elsevier, 2008)Voyager 1 crossed the solar wind termination shock on December 16, 2004 at a distance of 94 AU from the Sun, to become the first spacecraft to explore the termination shock region and to enter the heliosheath, the final ... -
The charge-sign dependent effect in the solar modulation of cosmic rays
Potgieter, M.S. (Elsevier, 2014)The centennial anniversary of the discovery of cosmic rays was in 2012. Since this discovery considerable progress has been made on several aspects related to galactic cosmic rays in the heliosphere. It is known that they ... -
Charge-sign dependent modulation of cosmic ray electrons and positrons up to extreme solar maximum conditions
Raath, J.L.; Potgieter, M.S. (PoS, 2017)The charge-sign dependent modulation of cosmic rays is an important topic in solar modulation studies, providing insights into gradient, curvature, and current sheet drifts. Such studies, at higher levels of solar activity, ... -
The combined modulation of Jovian and Galactic electrons in the heliosphere
Potgieter, Marius S.; Nndanganeni, Rendani R. (PoS, 2017)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 ... -
Comparative time-series analysis of MeV electron data by Ulysses and Pioneer 10/11 in the Jovian magnetosphere
Dunzlaff, P.; Kopp, A.; Potgieter, M.S.; Heber, B. (Copernicus Publications, 2013)The dynamics of the Jovian magnetosphere is dominated by the planet’s fast rotation with a period of 10 h.Within the magnetosphere, this periodicity can in particular be seen in the temporal variation of the spectral index ... -
Constraints on the lepton content of PWN from the local CR positron spectrum
Büsching, I.; De Jager, O.C.; Potgieter, M.S.; Venter, C. (ICRC, 2008)Geminga is a nearby pulsar with an age of 3.42×105 yr and a spindown power of 3.2×1034 erg/s at present. B0656+14 has comparable spindown power, with an age of 1.11×105 yr and a distance of 290 pc. The winds of these ... -
Cosmic ray flux at the earth in a variable heliosphere
Scherer, K.; Ferreira, S.E.S.; Potgieter, M.S.; Fichtner, H.; Heber, B. (Elsevier, 2008)In recent years the variability of the cosmic ray flux has become one of the main issues not only for the interpretation of the abundances of cosmogenic isotopes in cosmochronic archives like, e.g., ice cores, but also for ... -
Cosmic ray modulation beyond the heliopause: a hybrid modeling approach
Strauss, R.D.; Potgieter, M.S.; Ferreira, S.E.S.; Fichtner, H.; Scherer, K. (IOP Publishing, 2013)Results from a newly developed hybrid cosmic ray (CR) modulation model are presented. In this approach, the transport of CRs is computed by incorporating the plasma flow from a magnetohydrodynamic model for the heliospheric ... -
Cosmic ray modulation in the outer heliosphere: predictions for cosmic ray intensities up to the heliopause along Voyager 1 and 2 trajectories
Manuel, R.; Ferreira, S.E.S.; Potgieter, M.S. (Elsevier, 2011)Time dependent cosmic ray modulation in the outer heliosphere is calculated and results are compared to Voyager 1 and 2 observations using a two-dimensional time-dependent cosmic ray transport model. We predict possible ... -
Cosmic rays in the dynamic heliosheath
Ferreira, S.E.S.; Potgieter, M.S.; Scherer, K. (Elsevier, 2008)Cosmic ray modulation in the outer heliosphere is discussed from a modeling perspective. Emphasis is on the transport and acceleration of these particles at and beyond the solar wind termination shock in the inner heliosheath ... -
Cosmic rays in the dynamic heliosphere
Potgieter, Marius S. (Japan Society of Plasma Science and Nuclear Fusion Research, 2009)he relation between the dynamics of the heliosphere, its shape and geometry, so lar activity and cosmic ray variations is addressed. The global features of the helio sphere influence what happens inside its boundaries ... -
Cosmic rays in the inner heliosphere: insights from observations, theory and models
Potgieter, M.S. (Springer, 2011)The global modulation of galactic cosmic rays in the inner heliosphere is determined by four major mechanisms: convection, diffusion, particle drifts (gradient, curvature and current sheet drifts), and adiabatic energy ... -
A cosmic-ray positron anisotropy due to two middle-aged, nearby pulsars?
Büsching, I.; De Jager, O.C.; Potgieter, M.S.; Venter, C. (IOP Publishing, 2008)Geminga and B0656+14 are the closest pulsars with characteristic ages in the range of 100 kyr to 1 Myr. They both have spin-down powers of the order 3 × 1034 ergs s–1 at present. The winds of these pulsars had most probably ... -
Cosmic-ray transport in heliospheric magnetic structures. II. Modeling particle transport through corotating interaction regions
Kopp, Andreas; Raath, Jan Louis; Potgieter, Marius S.; Wiengarten, Tobias; Fichtner, Horst (IOP, 2017)The transport of cosmic rays (CRs) in the heliosphere is determined by the properties of the solar wind plasma. The heliospheric plasma environment has been probed by spacecraft for decades and provides a unique opportunity ... -
Difference in the heliospheric modulation of cosmic-ray protons and electrons during the solar minimum period of 2006 to 2009
Potgieter, M.S.; Vos, E.E. (EDP Sciences, 2017)Context. The PAMELA experiment observed galactic proton and electron spectra down to 70 MV and 400 MV, respectively, from mid-2006 to the end of 2009 during what is called an A < 0 solar magnetic polarity cycle. During ... -
The dynamic heliosphere, solar activity, and cosmic rays
Potgieter, Marius S. (Elsevier, 2010)This brief review addresses the relation between solar activity, cosmic ray variations and the dynamics of the heliosphere. The global features of the heliosphere influence what happens inside its boundaries on a variety ... -
The effect of a dynamic inner heliosheath thickness on cosmic-ray modulation
Manuel, R.; Ferreira, S.E.S.; Potgieter, M.S. (IOP Publishing, 2015)The time-dependent modulation of galactic cosmic rays in the heliosphere is studied over different polarity cycles by computing 2.5 GV proton intensities using a two-dimensional, time-dependent modulationmodel. By ... -
Electron anisotropies in the inner heliosphere
Nkosi, G.S.; Potgieter, M.S.; Ferreira, S.E.S. (Elsevier, 2008)A three-dimensional numerical model is used to study the propagation and modulation of a few MeV Jovian and galactic electrons in the inner heliosphere. The main aim of the work is to compute the three-dimensional electron ...