Multi-instrument observations of ionospheric irregularities over South Africa
- Authors: Amabayo, Emirant Bertillas
- Date: 2012
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5476 , http://hdl.handle.net/10962/d1005261 , Ionosphere -- Research , Sudden ionospheric disturbances , Ionospheric storms , Solar activity , Sunspots
- Description: The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes at Madimbo (30.88◦E, 22.38◦S), Grahamstown (33.32◦S, 26.50◦E) and Louisvale (28.51◦S, 21.24◦E). This study is intended to quantify the probability of the occurrence of F region disturbances associated with ionospheric spread F (SF) and L-band scintillation over South Africa. This study used available ionosonde data for 8 years (2000-2008) from the three South African stations. The SF events were identified manually on ionograms and grouped for further statistical analysis into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The results show that the diurnal pattern of SF occurrence peaks strongly between 23:00 and 00:00 UT. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown during 2001 and 2005, except for RSF which had peaks during autumn and spring during 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing sunspot number (SSN), with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study SF was evident in ∼ 0.03% and ∼ 0.06% of the available ionograms at Madimbo and Grahamstown respectively during the eight year period. The presence of ionospheric irregularities associated with SF and scintillation was investigated using data from selected Global Positioning System (GPS) receiver stations distributed across South Africa. The results, based on GPS total electron content (TEC) and ionosonde measurements, show that SF over this region can most likely be attributed to travelling ionospheric disturbances (TIDs), caused by gravity waves (GWs) and neutral wind composition changes. The GWs were mostly associated with geomagnetic storms and sub-storms that occurred during periods of high and moderate solar activity (2001-2005). SF occurrence during the low solar activity period (2006-2008)can probably be attributed to neutral wind composition changes.
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Perspectives on China's rise in Namibia: the effects on foreign policy and domestic politics
- Authors: Amadhila, Nelago Ndapandula Ndanyanyukwa
- Date: 2012
- Subjects: Namibia -- Relations -- China China -- Relations -- Namibia Namibia -- Politics and government -- Chinese influences Namibia -- Economic conditions -- Chinese influences
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2758 , http://hdl.handle.net/10962/d1002968
- Description: This thesis analyses the different levels at which China’s presence in Namibia affects Namibia’s domestic politics and foreign policy from a constructivist viewpoint. Constructivist theory is used to examine the different perceptions of the Chinese in Namibia and how these inform Namibian politics and Sino-Namibian relations. These perceptions are formed at different levels of society in formal and informal relations, state-to-state, state-to-business,business-to-business and individual-to-group relations. The way in which perceptions of Chinese involvement in Namibia at the grassroots level of society differ from those at the top increasingly has an effect on domestic Namibian politics and, as such, Sino-Namibian relations. This identifies official and non-official perceptions of China’s political, economic and social presence to determine the effects of grassroots on China vis-à-vis official perceptions in Namibian politics and the effects of grassroots views on Namibian politics and on official views and state behaviour towards China and China’s presence in the country.
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