An investigation of traveling ionospheric disturbances (TIDs) in the SANAE HF radar data
- Authors: Atilaw, Tsige Yared
- Date: 2022-04-07
- Subjects: Ionospheric storms Antarctica , Radar Antarctica , Range time-intensity (RTI) , South African National Antarctic Expedition (SANAE) , Super Dual Auroral Radar Network (SuperDARN)
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232377 , vital:49986 , DOI 10.21504/10962/232377
- Description: This thesis aims to study the characteristics of traveling ionospheric disturbances (TIDs) as identified in the radar data of the South African National Antarctic Expedition (SANAE) Super Dual Auroral Radar Network (SuperDARN) radar located in Antarctica. For this project, 22 TIDs were identified from visual inspection of range time-intensity (RTI) plots of backscattered power and Doppler velocity parameters of the SANAE radar between 2005âAS2015. These events were studied to determine their characteristics and driving mechanisms. Where good quality data were available, the SANAE HF radar data were supplemented by Halley radar data, which has large area of overlapping field of view (FOV) with the SANAE radar, and also by GPS TEC data. This provided a multi-instrument data analysis of some TID events. Different spectral analysis methods, namely the multitaper method (MTM), Fast Fourier transform (FFT) and the Lomb-Scargle periodogram were used to obtain spectral information of the observed waves. The advantage of using multiple windowing in MTM over the traditional windowing method was illustrated using one of the TID events. In addition, the analytic signal of the wave from the MTM method was used to estimate the instantaneous phase velocity and propagation azimuth of the wave, which was able to track the change in the characteristics of the medium-scale TID (MSTID) efficiently throughout the duration of the event. This is a clear advantage over other windowing techniques. The energy contribution by this MSTID through Joule heating was estimated over the region where spectral analysis of both SANAE and Halley data showed it to be present. The majority of the TIDs (65.4%) could be classified as MSTIDs with periods of 20–60 minutes, velocities of 50–333 ms1 and wavelengths of 129–833 km. The TID occurrence rate was high around the March equinox with 12 out of the 16 event days being during March–May. March had a particularly high number of occurrences of TIDs (46%). The majority of the TIDs observed during this month propagated northward or southeastward. In terms of prevailing geomagnetic conditions, 6 out of 16 event days were geomagnetically quiet, while 10 occurred during geomagnetic storms and substorms. During quiet conditions, TIDs could be linked to Es and polarised electric fields in 2 of these events. The other quiet time events could not be related to Es instability and polarised electric field either because their exact propagation direction could not be determined or data quality from the Es region scatter was too poor to perform spectral analysis. The storm-/substorm-related TIDs are possibly generated through Joule heating, the Lorentz force and energetic particle precipitation. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
- Authors: Atilaw, Tsige Yared
- Date: 2022-04-07
- Subjects: Ionospheric storms Antarctica , Radar Antarctica , Range time-intensity (RTI) , South African National Antarctic Expedition (SANAE) , Super Dual Auroral Radar Network (SuperDARN)
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232377 , vital:49986 , DOI 10.21504/10962/232377
- Description: This thesis aims to study the characteristics of traveling ionospheric disturbances (TIDs) as identified in the radar data of the South African National Antarctic Expedition (SANAE) Super Dual Auroral Radar Network (SuperDARN) radar located in Antarctica. For this project, 22 TIDs were identified from visual inspection of range time-intensity (RTI) plots of backscattered power and Doppler velocity parameters of the SANAE radar between 2005âAS2015. These events were studied to determine their characteristics and driving mechanisms. Where good quality data were available, the SANAE HF radar data were supplemented by Halley radar data, which has large area of overlapping field of view (FOV) with the SANAE radar, and also by GPS TEC data. This provided a multi-instrument data analysis of some TID events. Different spectral analysis methods, namely the multitaper method (MTM), Fast Fourier transform (FFT) and the Lomb-Scargle periodogram were used to obtain spectral information of the observed waves. The advantage of using multiple windowing in MTM over the traditional windowing method was illustrated using one of the TID events. In addition, the analytic signal of the wave from the MTM method was used to estimate the instantaneous phase velocity and propagation azimuth of the wave, which was able to track the change in the characteristics of the medium-scale TID (MSTID) efficiently throughout the duration of the event. This is a clear advantage over other windowing techniques. The energy contribution by this MSTID through Joule heating was estimated over the region where spectral analysis of both SANAE and Halley data showed it to be present. The majority of the TIDs (65.4%) could be classified as MSTIDs with periods of 20–60 minutes, velocities of 50–333 ms1 and wavelengths of 129–833 km. The TID occurrence rate was high around the March equinox with 12 out of the 16 event days being during March–May. March had a particularly high number of occurrences of TIDs (46%). The majority of the TIDs observed during this month propagated northward or southeastward. In terms of prevailing geomagnetic conditions, 6 out of 16 event days were geomagnetically quiet, while 10 occurred during geomagnetic storms and substorms. During quiet conditions, TIDs could be linked to Es and polarised electric fields in 2 of these events. The other quiet time events could not be related to Es instability and polarised electric field either because their exact propagation direction could not be determined or data quality from the Es region scatter was too poor to perform spectral analysis. The storm-/substorm-related TIDs are possibly generated through Joule heating, the Lorentz force and energetic particle precipitation. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2022
- Full Text:
Exploring structures and beliefs underlying textbook praxis in German foreign language courses at a South African university – a social realist perspective
- Authors: Engelbrecht, Natasha
- Date: 2022-04-07
- Subjects: German language Study and teaching (Higher) English speakers , Curriculum change South Africa , German language Textbooks History and criticism , Common European Framework of Reference for Languages (Project) , Decolonization South Africa , Educational change South Africa , Social realism
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232657 , vital:50011 , DOI https://doi.org/10.21504/10962/232657
- Description: Commercial textbooks, aligned with the Common European Framework of Reference for Languages (CEFR), are prescribed in almost all undergraduate GFL courses offered at South African universities. Although providing practical relevance and quality assurance, the CEFR-level descriptors were developed for the European context. The projected relevance and appropriateness of teaching materials presently implemented in German curricula in South African higher education have been determined in Germany, not for local contexts, but for learners vaguely described as “Anfänger” (Evans, et al., 2012, p. 8) and “Erwachsene und Jugendliche ab 16 Jahren” (Hueber, 2019, p. 11), often with a focus on learning for prospective German immigrants or for the use in refugee- or immigrant integration courses. However, the textbook occupies a central position in the GFL course because of the structured grammar progression that it lends to the curriculum. The variety of resources available to lecturers (tests, worksheets, online learning platform) and students (exercises, English-German glossary, English grammar explanations) is also an asset to GFL courses. Calls for the transformation and decolonisation of higher education have prompted academic disciplines to re-evaluate the common-sense assumptions which underpin knowledge practices in their curriculum. Following a social realist perspective and an exploratory case-study approach, this study presents a critical analysis of the textbook prescribed in the German Studies 1 course at Rhodes University and student experiences of the textbook to disentangle the complex relations which cause textbook praxis and lay bare power structures and tensions in the system. , Thesis (PhD) -- Humanities, School of Languages and Literatures, 2022
- Full Text:
- Authors: Engelbrecht, Natasha
- Date: 2022-04-07
- Subjects: German language Study and teaching (Higher) English speakers , Curriculum change South Africa , German language Textbooks History and criticism , Common European Framework of Reference for Languages (Project) , Decolonization South Africa , Educational change South Africa , Social realism
- Language: English
- Type: Doctoral thesis , text
- Identifier: http://hdl.handle.net/10962/232657 , vital:50011 , DOI https://doi.org/10.21504/10962/232657
- Description: Commercial textbooks, aligned with the Common European Framework of Reference for Languages (CEFR), are prescribed in almost all undergraduate GFL courses offered at South African universities. Although providing practical relevance and quality assurance, the CEFR-level descriptors were developed for the European context. The projected relevance and appropriateness of teaching materials presently implemented in German curricula in South African higher education have been determined in Germany, not for local contexts, but for learners vaguely described as “Anfänger” (Evans, et al., 2012, p. 8) and “Erwachsene und Jugendliche ab 16 Jahren” (Hueber, 2019, p. 11), often with a focus on learning for prospective German immigrants or for the use in refugee- or immigrant integration courses. However, the textbook occupies a central position in the GFL course because of the structured grammar progression that it lends to the curriculum. The variety of resources available to lecturers (tests, worksheets, online learning platform) and students (exercises, English-German glossary, English grammar explanations) is also an asset to GFL courses. Calls for the transformation and decolonisation of higher education have prompted academic disciplines to re-evaluate the common-sense assumptions which underpin knowledge practices in their curriculum. Following a social realist perspective and an exploratory case-study approach, this study presents a critical analysis of the textbook prescribed in the German Studies 1 course at Rhodes University and student experiences of the textbook to disentangle the complex relations which cause textbook praxis and lay bare power structures and tensions in the system. , Thesis (PhD) -- Humanities, School of Languages and Literatures, 2022
- Full Text:
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