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.
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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.
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