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.
- Full Text:
- Date Issued: 2012
- 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.
- Full Text:
- Date Issued: 2012
Variability of the peak height of the ionospheric F2 layer over South Africa
- Authors: Mbambo, Makhangela Casey
- Date: 2011
- Subjects: Ionosphere -- South Africa , Ionosphere -- Observations , Ionosphere -- Research , Double layers (Astrophysics)
- Language: English
- Type: Thesis , Masters , MSc (Physics)
- Identifier: vital:11594 , http://hdl.handle.net/10353/446 , Ionosphere -- South Africa , Ionosphere -- Observations , Ionosphere -- Research , Double layers (Astrophysics)
- Description: Abstract This thesis will present an investigation into the variability of the maximum height of the ionospheric F2 layer, hmF2, with hour, season and latitude over the South African region. The dependence of hmF2 on solar and magnetic activity is also investigated. Data from three South African stations, namely Madimbo (22.4 S, 26.5 E), Grahamstown (33.3 S, 26.5 E) and Louisvale (28.5 S, 21.2 E) were used in this study. Initial results indicate that hmF2 shows a larger variability around midnight than during daytime for all the seasons. Monthly median values for hmF2 were used in all cases to illustrate the variability, and the International Reference Ionosphere (IRI) model has been used to investigate hmF2 predictability over South Africa. This research represents the initial steps towards a predictive model for the hmF2 parameter, with the long term aim of developing a new global hmF2 predictive model for the IRI. It is believed that this work will contribute signi cantly towards this aim through the understanding of the hmF2 parameter over a region that has not previously been investigated.
- Full Text:
- Date Issued: 2011
- Authors: Mbambo, Makhangela Casey
- Date: 2011
- Subjects: Ionosphere -- South Africa , Ionosphere -- Observations , Ionosphere -- Research , Double layers (Astrophysics)
- Language: English
- Type: Thesis , Masters , MSc (Physics)
- Identifier: vital:11594 , http://hdl.handle.net/10353/446 , Ionosphere -- South Africa , Ionosphere -- Observations , Ionosphere -- Research , Double layers (Astrophysics)
- Description: Abstract This thesis will present an investigation into the variability of the maximum height of the ionospheric F2 layer, hmF2, with hour, season and latitude over the South African region. The dependence of hmF2 on solar and magnetic activity is also investigated. Data from three South African stations, namely Madimbo (22.4 S, 26.5 E), Grahamstown (33.3 S, 26.5 E) and Louisvale (28.5 S, 21.2 E) were used in this study. Initial results indicate that hmF2 shows a larger variability around midnight than during daytime for all the seasons. Monthly median values for hmF2 were used in all cases to illustrate the variability, and the International Reference Ionosphere (IRI) model has been used to investigate hmF2 predictability over South Africa. This research represents the initial steps towards a predictive model for the hmF2 parameter, with the long term aim of developing a new global hmF2 predictive model for the IRI. It is believed that this work will contribute signi cantly towards this aim through the understanding of the hmF2 parameter over a region that has not previously been investigated.
- Full Text:
- Date Issued: 2011
Some ionospheric effects observed at sunrise
- Authors: Baker, D C
- Date: 1964
- Subjects: Sun -- Rising and setting , Ionosphere -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5513 , http://hdl.handle.net/10962/d1009496 , Sun -- Rising and setting , Ionosphere -- Research
- Description: The study of the ionosphere over the sunrise period is necessary for an understanding of the vtiriations in layer structure with time and has been a topic of research of many workers. On the whole these investigations have been restricted to a study of critical frequency variations with relatively short intervals of a few minutes between successive records, of N-h curves deduced from ionograms with long intervals (15 minutes or so) between successive N-h curves or of continuously monitored single frequency reflections. Not one of the three techniques is entirely satisfactory for a detailed study of ionospheric behaviour over sunrise. The first two do not give a sufficiently clear indication of what happens in the initial stages of layer development, while from the third incomplete data is obtained as to what is happening at a specific electron-density level. For this reason a preliminary investigation of the ionosphere over sunrise was made at Rhodes University during August, 1959. The records were obtained at four-and-a-half minute intervals and scaled by the method of KELSO (1952 ). "Many of t he results were inconclusive but it appeared that records would have to be taken at approximately one minute intervals and reduced to N-h curves by a scaling technique which made full allowance for low-level ionization if useful results were to be obtained. An attempt has been made in this thesis to investigate the behaviour of the ionosphere over sunrise more fully than can be done by the three techniques referred to. A number of observed phenomena are also examined. Part I deals with the theoretical background to ionosphere physics in general and describes the equipment, equipment modifications and experimental procedure. Part II presents the results obtained. The records for a largescale travelling disturbance are analysed. Various observed phenomena are described and discussed. A simple method of obtaining production rates from experimental data is described. The implications of the observed variations of production rates with height and time are discussed. Suggestions for further research and improvement of the methods used arc made in Charter 9.
- Full Text:
- Date Issued: 1964
- Authors: Baker, D C
- Date: 1964
- Subjects: Sun -- Rising and setting , Ionosphere -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5513 , http://hdl.handle.net/10962/d1009496 , Sun -- Rising and setting , Ionosphere -- Research
- Description: The study of the ionosphere over the sunrise period is necessary for an understanding of the vtiriations in layer structure with time and has been a topic of research of many workers. On the whole these investigations have been restricted to a study of critical frequency variations with relatively short intervals of a few minutes between successive records, of N-h curves deduced from ionograms with long intervals (15 minutes or so) between successive N-h curves or of continuously monitored single frequency reflections. Not one of the three techniques is entirely satisfactory for a detailed study of ionospheric behaviour over sunrise. The first two do not give a sufficiently clear indication of what happens in the initial stages of layer development, while from the third incomplete data is obtained as to what is happening at a specific electron-density level. For this reason a preliminary investigation of the ionosphere over sunrise was made at Rhodes University during August, 1959. The records were obtained at four-and-a-half minute intervals and scaled by the method of KELSO (1952 ). "Many of t he results were inconclusive but it appeared that records would have to be taken at approximately one minute intervals and reduced to N-h curves by a scaling technique which made full allowance for low-level ionization if useful results were to be obtained. An attempt has been made in this thesis to investigate the behaviour of the ionosphere over sunrise more fully than can be done by the three techniques referred to. A number of observed phenomena are also examined. Part I deals with the theoretical background to ionosphere physics in general and describes the equipment, equipment modifications and experimental procedure. Part II presents the results obtained. The records for a largescale travelling disturbance are analysed. Various observed phenomena are described and discussed. A simple method of obtaining production rates from experimental data is described. The implications of the observed variations of production rates with height and time are discussed. Suggestions for further research and improvement of the methods used arc made in Charter 9.
- Full Text:
- Date Issued: 1964
- «
- ‹
- 1
- ›
- »