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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