ETD Collection

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    Initial steps in the development of a comprehensive lightning climatology of South Africa
    (2009-07-08T07:14:57Z) Gill, Tracey
    The summer rainfall region of South Africa is dominated by convective thunderstorm development from October to March. The result is that lightning is a common event over most of the country during this time. The South African Weather Service (SAWS) installed a stateof- the-art Lightning Detection Network (LDN) in late 2005 in order to accurately monitor lightning across South Africa. Data from this network for 2006 was utilised in order to develop an initial climatology of lightning in South Africa. Analyses were performed of lightning ground flash density, flash median peak current and flash multiplicity on a 0.2° grid across South Africa. The highest ground flash density values were found along the eastern escarpment of the country, extending onto the high interior plateau. There is a general decrease in flash density from east to west, with almost no lightning recorded on the west coast of the country. The regions of highest flash density recorded the highest percentages of negative polarity lightning. The percentage of positive lightning was higher in the winter months, as was the median peak current of lightning of both polarities. The median peak current distribution displayed distinct bands of current values oriented in northwest to southeast bands across the country. The bands of higher median peak current correspond to the regions to the rear of the interior trough axis in areas dominated by stratiform cloud development and were more dominant in the mid summer months. The highest flash multiplicity was recorded in the regions of highest flash density. Along the southern escarpment, on the eastern side of South Africa, flash multiplicity values exceeded 3 flashes per square kilometer. The highest flash multiplicity of negative polarity lightning was recorded in the spring and early summer. Throughout the year, the percentage of single stroke flashes for positive lightning is high. Topography and the position of the surface trough have a very strong influence on the ground flash density and median peak current distributions, but not on the flash multiplicity distribution. The results from the analyses of the three lightning variables were then combined to determine risk indexes of high intensity lightning and of positive polarity lightning. The eastern part of South Africa is at extreme risk from both large amounts of lightning and from positive polarity lightning, whereas the regions in the northwest of the country that are dominated by mining are at extreme risk from mainly positive polarity lightning.
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    A COMPARISON OF TEACHER STRESS, COMMITMENT AND SCHOOL CLIMATE IN SCHOOLS WITH DIFFERENT SUCCESS RATES
    (2006-11-16T10:25:11Z) Khoza, Harriet Rivalani
    It has been established that South African schools often experience vastly different matric success rates, even in schools from the same areas, with similar resources (Snyman, 1998). This study was conducted to compare teacher stress, professional commitment and school climate in schools with different matric success rates, in an attempt to uncover some of the reasons behind differing pass rates. The sample consisted of teachers from four high schools with different matric pass rates. The schools were selected from twelve high schools in the same rural area, same education district and circuit. The two high schools which performed very badly were matched with two high schools which produced a hundred percent pass rate in their recent matric results. A questionnaire was used as a data collection instrument. The questionnaires consisted of the Job Stress Survey, Professional Commitment Scale, as well as the Organisational Climate Index. The research questions for the study were: (i) Do teachers from schools with different matric success rates perceive the same sources of stress? (ii) Are teachers in schools with different matric pass rates experiencing the same levels of stress? (iii) Is there any difference between teachers’ perceptions of school 6 climate in schools with different matric pass rates? (iv) Do teachers in schools with different matric success rates differ in terms of their levels of professional commitment? The results indicated similarities in terms of the levels and sources of stress among the teachers from the two school types, as no significant differences between the schools were found. However, the teachers in schools with excellent matric pass rates have higher levels of commitment, and perceive their schools more favourably than the teachers in schools with poor matric pass rates. Significant correlations were also found to exist between teachers’ professional commitment and organisational climate. These findings indicate that there is a need in South Africa to seek out ways of improving the climate of the schools as well as teachers’ professional commitment in order to produce quality education.