Statistical analysis of travelling ionospheric disturbances during geomagnetic storms
- Authors: Mothibi, Matsobane Alex
- Date: 2025-04-02
- Subjects: Sudden ionospheric disturbances , Geomagnetic storm , Solar flares , Global Positioning System , Gravity waves
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479138 , vital:78264
- Description: This thesis presents observations of medium to large-scale traveling ionospheric disturbances (TIDs) originating from high latitudes, and propagating towards the equator and TIDs originating from the equator with a poleward propagation in the African-European sector during geomagnetically disturbed conditions between 2006 and 2022. 196 TID activities propagating over the African-European sector were observed, of these TID activities, 161 and 33 were observed during geomagnetic storms, and simultaneous occurrence of geomagnetic storms and solar flares, respectively. Total electron content perturbations derived from Global Navigation Satellite Systems (GNSS) observations within a latitude range of 40°S–60°N and longitude ranges of 20°-40°E representing the African-European sector were analysed based on the storm criteria of Dst ≤ -30 nT. The GNSS total electron content (TEC) data were used to obtain the two dimensional (2d) TEC perturbations. The northern hemispheric part of the African sector has limited data coverage which is visualized by a gap around 20°, where there were no data coverage can be observed in the 2d TEC maps. An important result is that large-scale TIDs (LSTIDs) and medium-scale TIDs (MSTIDs) were found to occur predominantly during the main and recovery phases of geomagnetic storms respectively, at least over the African-European sector. During the main phase of storms equatorward LSTID activity was relatively consistent across both hemispheres, with years of solar maximum, between 2013 and 2015, showing higher frequencies of events. Equatorward MSTID activity appeared less frequent overall, particularly in the southern hemisphere (SH), suggesting that equatorward LSTID activity are more prominent during the main phase of geomagnetic storms. Poleward TID activity were more predominant in the recovery phase than the main phase of geomagnetic storms. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2025
- Full Text:
- Date Issued: 2025-04-02
- Authors: Mothibi, Matsobane Alex
- Date: 2025-04-02
- Subjects: Sudden ionospheric disturbances , Geomagnetic storm , Solar flares , Global Positioning System , Gravity waves
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479138 , vital:78264
- Description: This thesis presents observations of medium to large-scale traveling ionospheric disturbances (TIDs) originating from high latitudes, and propagating towards the equator and TIDs originating from the equator with a poleward propagation in the African-European sector during geomagnetically disturbed conditions between 2006 and 2022. 196 TID activities propagating over the African-European sector were observed, of these TID activities, 161 and 33 were observed during geomagnetic storms, and simultaneous occurrence of geomagnetic storms and solar flares, respectively. Total electron content perturbations derived from Global Navigation Satellite Systems (GNSS) observations within a latitude range of 40°S–60°N and longitude ranges of 20°-40°E representing the African-European sector were analysed based on the storm criteria of Dst ≤ -30 nT. The GNSS total electron content (TEC) data were used to obtain the two dimensional (2d) TEC perturbations. The northern hemispheric part of the African sector has limited data coverage which is visualized by a gap around 20°, where there were no data coverage can be observed in the 2d TEC maps. An important result is that large-scale TIDs (LSTIDs) and medium-scale TIDs (MSTIDs) were found to occur predominantly during the main and recovery phases of geomagnetic storms respectively, at least over the African-European sector. During the main phase of storms equatorward LSTID activity was relatively consistent across both hemispheres, with years of solar maximum, between 2013 and 2015, showing higher frequencies of events. Equatorward MSTID activity appeared less frequent overall, particularly in the southern hemisphere (SH), suggesting that equatorward LSTID activity are more prominent during the main phase of geomagnetic storms. Poleward TID activity were more predominant in the recovery phase than the main phase of geomagnetic storms. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2025
- Full Text:
- Date Issued: 2025-04-02
Night-time gravity waves detected with multi-frequency airglow imager
- Authors: Machubeng, Karabo Pebane
- Date: 2021-04
- Subjects: Gravity waves , Airglow , Gravity waves -- Seasonal variations , All Sky Imager
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/178341 , vital:42931
- Description: This thesis shows the statistics of atmospheric gravity waves (AGWs) observed in the OI emission 557.7 nm at _97 km altitude using an all-sky imager based in Sutherland, South Africa (32.37_ S, 20.81_ E) in the year 2017. The wavelengths were determined using the propagation vector method, velocity was determined using the cross correlation of 1D FFT and the period was determined using the equation that relates wavelength and velocity. It was found that the horizontal wavelength in summer was almost evenly distributed between 10 and 40 km and for autumn, winter and spring were mostly between 10 and 30 km. The favoured speeds were between 40 and 50 m/s in autumn, as well as 30 and 50 m/s in summer, but the AGWs in winter had a bimodal speed distribution of 20 - 40 and 50 - 70 m/s. The majority of periods observed in all seasons were less than 20 minutes with a dominant peak of 5 - 10 minutes in autumn and spring. There was no favoured propagation direction for spring, but AGWs favoured a southeastward propagation in summer, and a southward propagation in autumn and winter. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Machubeng, Karabo Pebane
- Date: 2021-04
- Subjects: Gravity waves , Airglow , Gravity waves -- Seasonal variations , All Sky Imager
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/178341 , vital:42931
- Description: This thesis shows the statistics of atmospheric gravity waves (AGWs) observed in the OI emission 557.7 nm at _97 km altitude using an all-sky imager based in Sutherland, South Africa (32.37_ S, 20.81_ E) in the year 2017. The wavelengths were determined using the propagation vector method, velocity was determined using the cross correlation of 1D FFT and the period was determined using the equation that relates wavelength and velocity. It was found that the horizontal wavelength in summer was almost evenly distributed between 10 and 40 km and for autumn, winter and spring were mostly between 10 and 30 km. The favoured speeds were between 40 and 50 m/s in autumn, as well as 30 and 50 m/s in summer, but the AGWs in winter had a bimodal speed distribution of 20 - 40 and 50 - 70 m/s. The majority of periods observed in all seasons were less than 20 minutes with a dominant peak of 5 - 10 minutes in autumn and spring. There was no favoured propagation direction for spring, but AGWs favoured a southeastward propagation in summer, and a southward propagation in autumn and winter. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2021
- Full Text:
- Date Issued: 2021-04
Statistical study of traveling ionospheric disturbances over South Africa
- Authors: Mahlangu, Daniel Fiso
- Date: 2019
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Gravity waves , Magnetic storms
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76387 , vital:30556
- Description: This thesis provides a statistical analysis of traveling ionospheric disturbances (TIDs) in South Africa. The velocities of the TIDs were determined from total electron content (TEC) maps using particle image velocimetry (PIV). The periods were determined using Morlet function in wavelet analysis. The TIDs were grouped into four categories: daytime, twilight, nighttime TIDs, and those TIDs that occurred during magnetic storms. It was found that daytime medium scale TIDs (MSTIDs) propagated equatorward in all seasons (summer, autumn, winter, and spring), with velocities of about 114 to 213 m/s. Their maximum occurrence was in winter between 15:00 and 16:00 LT. The daytime large scale (TIDs) LSTIDs propagated equatorward with velocities of approximately 455 to 767 m/s. Their highest occurrence was in summer, between 12:00-13:00 LT. Most of the these TIDs (about 78%) were observed during the passing of the morning solar terminator. This implied that the morning terminator was more effective in instigating TIDs. Only a few nighttime TIDs were observed and therefore their behavior could not be statistically inferred. The TIDs that occurred during magnetically disturbed conditions propagated equatorward. This indicated that their source mechanism was atmospheric gravity waves generated at the onset of geomagnetic storms.
- Full Text:
- Date Issued: 2019
- Authors: Mahlangu, Daniel Fiso
- Date: 2019
- Subjects: Ionosphere -- Research , Sudden ionospheric disturbances , Gravity waves , Magnetic storms
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/76387 , vital:30556
- Description: This thesis provides a statistical analysis of traveling ionospheric disturbances (TIDs) in South Africa. The velocities of the TIDs were determined from total electron content (TEC) maps using particle image velocimetry (PIV). The periods were determined using Morlet function in wavelet analysis. The TIDs were grouped into four categories: daytime, twilight, nighttime TIDs, and those TIDs that occurred during magnetic storms. It was found that daytime medium scale TIDs (MSTIDs) propagated equatorward in all seasons (summer, autumn, winter, and spring), with velocities of about 114 to 213 m/s. Their maximum occurrence was in winter between 15:00 and 16:00 LT. The daytime large scale (TIDs) LSTIDs propagated equatorward with velocities of approximately 455 to 767 m/s. Their highest occurrence was in summer, between 12:00-13:00 LT. Most of the these TIDs (about 78%) were observed during the passing of the morning solar terminator. This implied that the morning terminator was more effective in instigating TIDs. Only a few nighttime TIDs were observed and therefore their behavior could not be statistically inferred. The TIDs that occurred during magnetically disturbed conditions propagated equatorward. This indicated that their source mechanism was atmospheric gravity waves generated at the onset of geomagnetic storms.
- Full Text:
- Date Issued: 2019
An investigation of the atmospheric wave dynamics in the polar region using ground based instruments
- Authors: Khanyile, Bhekumuzi Sfundo
- Date: 2011
- Subjects: Gravity waves , Atmospheric physics -- South Africa , Riometer , Gravity -- Measurement , Rossby waves
- Language: English
- Type: Thesis , Masters , MSc (Physics)
- Identifier: vital:11592 , http://hdl.handle.net/10353/447 , Gravity waves , Atmospheric physics -- South Africa , Riometer , Gravity -- Measurement , Rossby waves
- Description: Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.
- Full Text:
- Date Issued: 2011
An investigation of the atmospheric wave dynamics in the polar region using ground based instruments
- Authors: Khanyile, Bhekumuzi Sfundo
- Date: 2011
- Subjects: Gravity waves , Atmospheric physics -- South Africa , Riometer , Gravity -- Measurement , Rossby waves
- Language: English
- Type: Thesis , Masters , MSc (Physics)
- Identifier: vital:11592 , http://hdl.handle.net/10353/447 , Gravity waves , Atmospheric physics -- South Africa , Riometer , Gravity -- Measurement , Rossby waves
- Description: Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.
- Full Text:
- Date Issued: 2011
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