The role of radial perpendicular diffusion and latitude dependent acceleration along the solar wind termination shock
ABSTRACT A numerical model, based on Parker’s transport equation, describing the modulation of anomalous cosmic rays and containing diffusive shock acceleration is applied. The role of radial perpendicular diffusion at the solar wind termination shock, and as the dominant diffusion coefficient in the outer heliosphere, is studied, in particular the role it plays in the effectiveness of the acceleration of anomalous protons and helium when its latitude dependence is changed. It is found that the latitudinal enhancement of radial perpendicular diffusion towards the heliospheric poles and along the termination shock has a prominent effect on the acceleration of these particles. It results in a ‘break’ in the energy spectrum for anomalous protons at ∼6.0 MeV, causing the spectral index to change from E−1.38 to E−2.23, but for anomalous helium at ∼3.0 MeV, changing the spectral index from E−1.38 to E−2.30. When approaching the simulated TS, the changes in the modulated spectra as they unfold to a ‘steady’ power law shape at energies below 50 MeV are much less prominent as a function of radial distances when radial perpendicular diffusion is increased with heliolatitude.
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ABSTRACT: After the solar wind termination shock crossings of the Voyager spacecraft, the acceleration of anomalous cosmic rays has become a very contentious subject. In this paper we examine several topics pertinent to anomalous cosmic ray oxygen acceleration and transport using a numerical cosmic ray modulation model. These include the effects of drifts on a purely Fermi I accelerated spectra, the effects of introducing higher charge states of oxygen into the modulation model, examining the viability of momentum diffusion as a re-acceleration process in the heliosheath and examining energy spectra, and intensity gradients, in the inner heliosphere during consecutive drift cycles.Advances in Space Research 01/2011; 48(1):65-75. · 1.18 Impact Factor
Article: Time-dependent cosmic ray modulation[Show abstract] [Hide abstract]
ABSTRACT: Time-dependent cosmic ray modulation is calculated over multiple solar cycles using our well established two-dimensional time-dependent modulation model. Results are compared to Voyager 1, Ulysses and IMP cosmic ray observations to establish compatibility. A time-dependence in the diffusion and drift coefficients, implicitly contained in recent expressions derived by , , and , is incorporated into the cosmic ray modulation model. This results in calculations which are compatible with spacecraft observations on a global scale over consecutive solar cycles. This approach compares well to the successful compound approach of Ferreira and Potgieter (2004). For both these approaches the magnetic field magnitude, variance of the field and current sheet tilt angle values observed at Earth are transported time-dependently into the outer heliosphere. However, when results are compared to observations for extreme solar maximum, the computed step-like modulation is not as pronounced as observed. This indicates that some additional merging of these structures into more pronounced modulation barriers along the way is needed.Advances in Space Research 01/2011; · 1.18 Impact Factor
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ABSTRACT: A study has been done in Luvuvhu Catchment to develop a framework for effective community participation in water quality monitoring and management. Community participation and involvement in development has since the 1970s gathered momentum among the non-governmental organisations (NGOs) fraternity but has never gained clear status with Governments world over. In South Africa the policy and legal frameworks for community consultation, involvement and participation are clearly spelt out on paper starting with the country’s constitution. The division of the country into Water Management Areas (WMA) and the formation of Catchment Management Agencies (CMA), Water User Associations (WUAs) for example, was meant to increase participation of stakeholders including communities in the management of water resources. These efforts have not translated into effective participation by local communities in the management of water resources because there is no link between the national water quality management frameworks and community based development structures.An extensive review of development frameworks including community based structures has been undertaken. The most critical frameworks identified were the national water quality management framework (Directorate of Water Quality Monitoring and Catchment Management Agencies), community based structures and local government structures and systems (municipalities, provincial and national structures). There was no flow of information between the national water quality framework and community based development structures and therefore linkages were created between the lower tiers of the catchment management system (sub catchment fora and WUAs) to allow for information from the Directorate of Quality Monitoring to reach communities and vice versa. The lower tiers of the catchment management system should serve as specialised committees under the community development structures. The municipalities who control and fund development activities at community level should be linked to the catchment management system so that information can flow between the lower tiers of the catchment management system and communities on one hand and the municipalities on the other. The water quality monitoring information generated at community level should flow through community development structures, sub catchment fora, the Catchment Forum (where municipalities are members), the CMA and into the Directorate of Water Quality Monitoring.Physics and Chemistry of The Earth - PHYS CHEM EARTH. 01/2011; 36(14):1063-1070.