The role of radial perpendicular diffusion and latitude dependent acceleration along the solar wind termination shock
Unit for Space Physics and School of Physics, North-West University, 2520 Potchefstroom, South AfricaAdvances in Space Research (Impact Factor: 1.36). 01/2008; 41(2):368-372. DOI: 10.1016/j.asr.2006.11.025
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.
- [Show abstract] [Hide abstract]
ABSTRACT: Cosmic ray drift directions depend both on the charge of the particle population under consideration, as well as the heliospheric magnetic field polarity which oscillates within a ˜22 year cycle. The differences in the cosmic ray drift patterns between successive solar cycles manifest themselves in the sign of the latitudinal cosmic ray gradient. For positively charged particles, a positive latitudinal gradient is expected in the qA > 0 polarity cycle, while a negative value is expected in the qA < 0 cycle. For the first time observed radial and latitudinal values for anomalous cosmic ray oxygen are available in both of these cycles. In the present qA 0 cycle, the model predicts a positive latitudinal gradient but for the qA < 0 cycle a latitudinal gradient that is smaller and that can be either positive or negative. It is concluded that drifts and poleward diffusion set up competing latitudinal gradients in the qA < 0 cycle, with the resulting sign of the gradient determined by the most effective of the two processes.Journal of Geophysical Research Atmospheres 12/2010; 115(A12). DOI:10.1029/2010JA015690 · 3.43 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Context. Since the crossings of the solar wind termination shock by the Voyager 1 and 2 spacecraft, much speculation has surrounded the acceleration mechanism and region where the anomalous cosmic ray component is accelerated. A peculiar, and mostly overlooked feature of the observed anomalous oxygen spectrum near the termination shock, is the power law form of the roll-over (cut-off) at the high energy range of this spectrum. Aims: We investigate, using a numerical model, why this deviation from the expected exponential form of the cut-off part of the anomalous oxygen spectrum occurs, and if the observed power law form can be explained in terms of the acceleration of multiple charged anomalous oxygen. Methods: Multiple charged anomalous cosmic rays are incorporated in a numerical model, based on the standard Parker transport equation, including acceleration at the solar wind termination shock. This is done by specifying an energy dependent charge state, constrained by observations. Results: Comparing computational results with spacecraft observations, it is found that the inclusion of multiply charged anomalous cosmic rays in the modulation model can explain the observed spectrum of anomalous oxygen in the energy range from 10-70 MeV per nucleon. The more effective acceleration of these multiple charge anomalous particles at the solar wind termination shock causes a significant deviation from the usual exponential cut-off spectrum to display instead a power law decrease up to 70 MeV per nucleon where galactic oxygen starts to dominate. In addition, the model reproduces the features of multiple charged oxygen at Earth so that a good comparison is obtained between computations and observations.Astronomy and Astrophysics 04/2010; DOI:10.1051/0004-6361/200913866 · 4.38 Impact Factor
- [Show abstract] [Hide abstract]
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 Parts A/B/C 01/2011; 36(14):1063-1070. DOI:10.1016/j.pce.2011.08.006 · 1.48 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.