Planetary waves are known to play an important role in determining the annual variability in the severity of Antarctic ozone depletion. In this thesis, data obtained from the TOMS experiment on board the Nimbus-7 satellite are used to create global maps of total column ozone for each day from 1979 to 1992. Planetary wave morphology within these distributions is examined using spatial spectral analysis. The wave powers obtained are compared with a measure of the depth and area of the Antarctic ozone hole. A theoretical overview is given of middle atmosphere dynamics and how it influences the global distribution of ozone. Planetary waves play a predominant role in this dynamical distribution as they are responsible for the eddy transport of heat, momentum and long-lived tracers. A discussion of the equations of motion governing planetary wave propagation and their physical interpretation is given. The use of derived meteorological parameters, such as potential vorticity, in the study of planetary waves is developed. The theoretical tools, together with the equations of motion, are used to examine the excitation mechanisms for planetary waves. This theoretical analysis is also used to show that the strength of the westerly jet within the polar vortex determines which planetary wave modes can be expected in the geopotential height fields. In general only wavenumber 1 and 2 propagate during the Southern Hemisphere winter and the strength of these waves strongly modulates the severity of the Antarctic ozone depletion. Furthermore, the timing of the breakdown of the polar vortex is connected with the temporal variation of planetary wave power. A review of the current research in the field of planetary waves and the global distribution of ozone is given. To quantify planetary wave activity, spatial spectral analysis (Fourier Transforms) of midlatitude zonal profiles of total column ozone are used to calculate wave powers in the ozone distribution. Powers at wavenumber 1 to 6 are calculated for each day from 1979 to 1992 for both the Northern and Southern Hemispheres. The powers are seen to decrease with wavenumber throughout the year and the amplitude of wave modes 3 and higher is suppressed during the winter in accordance with the theoretical discussion. Southern Hemisphere wave powers are compared with a daily depleted mass of ozone over the Antarctic from 1979 to 1992. It is found that during years of high (low) planetary wave activity Antarctic ozone depletion is very weak (severe). Finally, the planetary wave morphology observed in the Southern Hemisphere total column ozone distribution is compared with geopotential height waves reported in the literature. Comparison of Northern Hemisphere wave powers and Arctic ozone depletion shows little or no correlation. To examine whether planetary waves may effect the interannual variability in Antarctic vortex temperatures, winter averaged 100 hPa upper air temperatures from SANAE (70°18' S, 2°21' W) are compared with derived planetary wave powers. It is found that during years of high (low) planetary wave activity the SANAE 100 hPa temperatures are above (below) the mean. Analysis of daily total column ozone and upper air temperatures at SANAE, during the winters of 1987 and 1988, shows that wave 1 forcing can significantly influence the day-to-day variation in these quantities. A statistical model of total ozone variation over the entire globe, from 1979 to 1992, has been developed. This model incorporates a long-term linear trend, an annual variation, a quasi-biennial oscillation, a solar cycle variation and a semiannual variation. Since monthly average total column ozone data are used in this model, short term planetary wave influences are masked, and the variations in global ozone are determined primarily by the 5 signals discussed above. However, analysis of the model coefficients indicates that planetary wave activity may significantly contribute to zonal asymmetry in global total ozone trends. Differences between model results and measured data are compared with planetary wave activity. The timing of the breakdown of the Antarctic circumpolar vortex causes large interannual differences in monthly average total column ozone for the months of October and November in the Southern Hemisphere. This analysis is made more specific for South Africa by examining the variation in monthly average total column ozone over the five South African cities of Pretoria, Bloemfontein, Durban, Port Elizabeth and Cape Town for the years 1979 to 1992. A model of surface erythemal irradiance as a function of total column ozone, time of the year and other meteorological parameters is developed. Total ozone data for the 5 cities, used within the context of the statistical model and the DV irradiance model, allows the prediction of future DV levels over South Africa to the year 2000. Planetary wave motion owes its existence to the conservation of potential vor-ticity. However, to make use of this conservation principle as a diagnostic for planetary wave propagation, it is necessary to know the conditions under which it is conserved. A formalism developed by Plumb and Ko (1992) has been used to suggest a technique whereby the 'lifetime' of potential vorticity may be determined. Use was made of data from the NCAR CCM2 model to test this hypothesis. The concentrations of long-lived tracers (CH4 and NzO) extracted from the CCM2 also show the effects of planetary wave breaking on the meridional distribution of these species. This study has important implications for airborne polar chemistry campaigns. / Thesis (Ph.D.)-University of Natal, 1994.

Whistlers have, for many years, been used as probes of the ionosphere and magnetosphere. Whistlers received on the ground have been shown (Smith [1961], Helliwell [1965]) to have propagated, in almost all cases, through ducts of enhanced ionisation aligned along the magnetic field direction. Analysis of these whistlers, using for example the Ho and Bernard [1973] method, allows determination of the L-value of the field line along which the signal has propagated, the equatorial electron density and the time of the initiating lightning strike. Satellite received whistlers, known as fractional-hop whistlers, are not restricted to propagating through ducts and, in this case, ducted whistlers are probably rarer than unducted whistlers. Analysis of these whistlers is consequently much more difficult as the propagation path is often not known. This study is an attempt to understand some of the characteristics of whistlers received on the 18182 satellite at low latitudes during October 1976. Haselgrove's [1954] ray tracing equations, together with realistic density and magnetic field models, have been used to determine the ray paths and travel times. The whistler dispersions, calculated from the travel times, are compared with the results obtained from analysis of the 18182 data. Values given by the density models used were also compared with density values obtained from other models and values recorded by ionosondes during the same period and at locations close to the latitude and longitude of the 18182 satellite. Another part of this study considers the cyclotron resonance interaction between ducted whistler mode waves and energetic electrons. During this interaction, electrons can diffuse into the loss cone and will then precipitate into the upper atmosphere causing secondary ionisation. This ionisation patch modifies the earthionosphere wave guide and can be observed as phase and/or amplitude perturbations on VLF transmitter signals, known as Trimpi events (Helliwell et al [1973], Dowden and Adams [1988], 1nan and Carpenter [1987]) . Trimpi events and associated whistlers were observed at Marion Island (46°53" 5, 37°52" E, L = 2.63) during May 1996. Analysis of the associated whistler groups confirms that the Trimpi events can be explained by the above mentioned cyclotron resonance interaction and subsequent electron precipitation. During this process the whistlers were propagating towards Marion Island while the electrons were propagating away. The electrons must therefore have mirrored in the northern hemisphere before precipitating near Marion Island causing the observed Trimpi. The calculated time delays are shown to confirm this process. During the unusual 2-hour period of observation, the Trimpi associated whistler groups were, in all cases, followed by a second, fainter whistler group which has been called a whistler 'ghost' . The dispersion of whistlers within this second whistler group are shown to be the same as those within the initial whistler group indicating that these whistlers must have propagated through common ducts at different times and hence must have been caused by different atmospheric discharges. It is thought that during the wave-particle interaction, which caused the observed Trimpi, some of the energetic electrons may have precipitated into the northern hemipshere triggering this second discharge. The timing between the two whistler groups is such that, if the above triggering is correct, the interaction must have taken place about 10° from the equatorial plane . / Thesis (Ph.D.)-University of Natal, 1997.

The interaction of laser light with a parcel of air with a known density structure can result in one of three reactions. The simplest of these reactions is reflection. Depending on the nature of the density profile, that part of the light that is not reflected can be refracted or scattered. The extent of the refraction and scattering is determined by the density of the particles found in the air. This thesis investigates two concepts that use the above mentioned interactions. The first, the colliding shock lens (CSL) was proposed by Buccellato, Lisi and Michaelis (1993). This device uses the graded index (GRIN) lens formed by the collision of symmetrically arranged shock waves to focus a laser beam. Unfortunately, the first reported colliding shock lenses had optical apertures of the order of millimeters. This is hardly useful in realistic laser systems whose beams typically have a diameter of 10mm. The major part of this thesis involves the scaling up of the optical aperture of the CSL while simultaneously maintaining a fairly short focal length. We show how the behaviour of the CSL varies with factors such as input energy, electrical diameter, geometry and various other factors. By optimising the physical parameters a 1.5cm diameter lens is obtained having a focal length of 1.5m. We develop a simple scaling theory and run a simulation based on the fluid in cell (FLIC) method, and find good correlation in both cases between the experimentally obtained results and the theoretically predicted ones. As a further development of the work on colliding shock lenses we introduce a cylindrical colliding shock lens. This device is shown to be able to line focus a laser beam of 1cm in diameter. At this stage the focus quality is still poor and suggestions are made for further improvements. Lidar is an acronym for light detection and ranging. Such systems are based on the scattering of laser light incident on a parcel of air. We discuss the results of a campaign conducted during the period of June to November 1994 to study aerosol concentrations over Durban. Particular attention is paid to low level aerosols due to sugar cane burning over the Natal coast. These aerosols are known to influence local climate and since vertical profile studies have never been carried out, this investigation gives some useful insight into the atmospheric dynamics. We find that in June (the begining of the burning campaign) the aerosol loading in the lower atmosphere is low. However, there are very stable aerosol layers at 3km and 5km. The density of the aerosols in these layers are decoupled. In September, the turbulent atmosphere over Durban is found to destroy structure in the aerosol layers. Nevertheless, the aerosol loading is high. Scattering ratios and extinction coefficients are calculated to show the long and short term evolution of the aerosols. A new coefficient (the low altitude aerosol coefficent - LAAC) is defined as an indicator for aerosol loading in the lower atmosphere. This coefficient is compared with total column ozone values over Durban. An anti-correlatory behaviour is noticed. We also report the detection of an extremely high aerosol layer (60km) over Durban. This layer is believed to be sodium. The profiles are compared to satellite data to verify the first ever detection of a constituent at these altitudes in Southern Africa. / Thesis (Ph.D.)-University of Natal, 1996.

This thesis begins with an introduction to the interaction and refraction of light in continuous media. It is shown how these properties can be exploited to achieve focusing of parallel light rays in such a medium. Past work on Gas Lenses is reviewed, highlighting the progress in design of gas lenses, leading to a justification for the research described in the rest of the chapter. Original work by the author on the subject of continuous gas lenses at low and high pressure is then presented. Experiments show that gas lenses at low pressure have stable foci, but long focal lengths, while at high pressure two foci are produced, both of unstable character. These results are explained by a simple theory, and future applications of such lensing properties are presented. Chapter two introduces the concept of the Colliding Shock Lens (CSL), and presents shallow water wave simulations, conducted by the author, as a useful analogy to the interaction of shocks in the CSL. All the properties of the CSL lensing action are reproduced in the water simulations, yielding useful insight, by means of a simple experiment, into the physics of interacting shock waves. Chapter three presents original work by the author on the subject of multiple pulse thermal lensing. A theory is developed which predicts the behaviour of thermal lenses seen in an industrial laser chain. Experiments on thermallensing, as well as some solutions, are presented and discussed. Chapter four revises the theory of Zernike Polynomials and their application to the study of aberrations. Thermal aberrations are studied, including the aberrations introduced by thermal lensing and thermal blooming. The relationship between aberrations and subsequent beam quality and beam propagation is explored. Chapter five looks at the use of adaptive mirrors for mode matching. Although the theory of adaptive systems is well known, no-one has as yet tackled the problem of correcting for mode matching changes. A new way of thinking about mode matching is proposed, and the merits of this system, called characterisation space, are explained. Chapter six comprises the theory and design of a novel vacuum chamber which has applications in gas lens designs. All the gas lenses used in pressure experiments were housed in compressional vacuum chambers. The idea of a Tensional Vacuum Vessel (TVV) is introduced, and experiments show that such chambers are very successful low vacuum chambers. The advantages and applications of TVVs are discussed, specifically those relating to gas lens applications. At the end of this thesis it was apparent that more questions had been generated than answers. This is probably true of any study. Chapter seven therefore outlines some as yet unanswered questions, and gives some suggestions for starting points. Some of this work is presently being undertaken by the author. / Thesis (Ph.D.)-University of Natal, 1997.

Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2011.

A magnetohydrodynamic (MHD) cavity-resonance model is developed to study the ultra low frequency (ULF) response in the magnetosphere to an external compressional impulse. It is assumed that the magnitude of the impulse is small enough such that non-linear terms remain negligible. The MHD differential equations are derived in a cold, non-uniform plasma imbedded in a cylindrical ambient field geometry and are solved using numerical finite difference integration methods. The crucial feature of the model is that it allows for the investigation of the response within the magnetospheric cavity to an impulse that has both temporal and spatial form. There is strong observational evidence that low-latitude Pi 2 pulsations have, or are associated with, a global propagation mechanism. Evidence alluding to the global nature of low-latitude Pi 2 is the characteristically low azimuthal (or axial) wavenumbers, (Irnl ;S 1 ). Further evidence of the global nature of Pi 2 is the lack of arrival time difference between globally separate events, as well as the similarity in the spectral content of globally separate events. As an application, the cavity-resonance model is applied to investigate the Pi 2 pulsation event. The cavity-resonance waves are excited by an impulsive perturbation at the magnetopause which is centred about the midnight meridian. The excitation signal is chosen representing the causal Pi 2 mechanism thought to be associated with the sudden, short circuiting of the cross-tail current to the auroral oval. Various aspects of the cavity-resonance wave modes are investigated and the appropriateness of this type of modelling for -the study of Pi 2 is evaluated. Numerical integration and well as Fourier and Laplace methods are used to investigate the transmission of the impulsive signal through the magnetosphere. Coupling between the isotropic (cavity) and the transverse Alfven (resonance) mode is studied. The effect of the plasmapause is considered. Longitudinal variations of polarization as well as the latitudinal phase variations of the perturbed fields are computed. Computational results are compared with observational features of the Pi 2 event. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

Many bulk properties of gases depend linearly on the gas density at lower densities, but as the density increases departures from linearity are observed. The density dependence of a bulk property Q may often be discussed systematically by expanding Q as a power series in l/Vm, to yield: Q=Aq+Bq/Vm+Cq/V2m+..., where Bq is known as the second virial coefficient of the property Q. Aq is the ideal gas value of Q, and Bq describes the contribution of molecular pair interactions to Q. Theories of Q may be regarded as having two main components, one describing how the presence of a neighbour of a given molecule can enhance or detract from its contribution to Q, and the other the molecular interaction energy which determines the average geometry of a pair encounter. The latter component is common to all theories, and the former requires detailed derivations for each specific bulk property Q. In this work we consider the second virial coefficients of five effects, namely the second pressure virial coefficient B(T), and also the second dielectric, refractivity, Kerr-effect and light-scattering virial coefficients, Be, Br, Bk, and Bp, respectively. Using a powerful computer algebraic manipulation package we have extended the existing dipole-induced-dipole (DID) theories of the second dielectric, refractivity and Kerr-effect virial coefficients to sufficiently high order to establish convergence in the treatment of both linear and non-linear gases. Together with the established linear theory of the second pressure virial coefficient, the extended theory of the second light- scattering virial coefficient developed by Couling and Graham, and their new non-linear theory of the second pressure and light-scattering virial coefficients, our new theories provide a comprehensive base from which to calculate numerical values for the various effects for comparison with experiment. We have collected as much experimental data of the various second virial coefficients as possible, for a wide range of gases. The ten gases chosen for detailed study comprise a selection of polar and non-polar, linear and non-linear gases: the linear polar gases fluoromethane, trifluoromethane, chloromethane and hydrogen chloride; the non-polar linear gases nitrogen, carbon dioxide and ethane; the non-linear polar gases sulphur dioxide and dimethyl ether; and the non-linear non-polar gas ethene. Using the best available measured or calculated molecular parameter data for these gases, together with the complete theories for the second virial coefficients, we have attempted to find unique sets of molecular parameters for each gas which explain all the available experimental data. In general, reliable measured or calculated molecular properties are regarded as fixed, and only the Lennard-Jones and shape parameters in the molecular interaction energy are treated as best-fit parameters within the constraints of being physically reasonable. Many of the apparent failures of second virial coefficient theories have been due to the lack of convergence in the series of terms evaluated. It is essential to work to sufficiently high orders in the polarizabilities and various multipole moments to ensure convergence for meaningful comparison with experiment. This often requires the manipulation of extremely long and complicated expressions, not possible by the manual methods of our recent past. The advent of computer manipulation packages and fast processors for numerical integration have now enabled calculation to high orders, where the degree of convergence can be sensibly followed. Our efforts to describe all of the effects for which data is available met with mixed success. For four of the gases, fluoromethane, chloromethane, dimethyl ether and ethene, a unique parameter set was found for each which described all of the available effects reasonably well. For the three gases, trifluoromethane, nitrogen and sulphur dioxide, one interaction parameter set explained all but one of the effects for which data was available to within experimental uncertainty. For trifluoromethane the parameter set which yielded good agreement for B(T), Be, and Bk could not explain the observed values of Br, while for nitrogen one parameter set produced reasonable agreement for all of the effects except Bp and a different set, which yielded good agreement for Bp, did not explain the remaining four effects as well as the first set. The parameter set which explained B(T), Bk and Bp very well for sulphur dioxide, yielded a value for Be, which was much larger than the experimental value, although of the correct sign and order of magnitude. Hydrogen chloride posed a special problem as data was only available for two of the effects, B(T) and Be. It was possible to find a set of interaction parameters in good agreement with the measured values of B(T), but the experimental data for Be was an order of magnitude larger than the largest calculated values. Since the remaining effects have not been measured for this gas it was not possible to test the theory more rigorously. For the remaining gases carbon dioxide and ethane, it was impossible, based on the existing measured values, to select a unique parameter set which explained all of the effects. In many of the cases where definite conclusions could not be drawn, it was not possible to decide whether the disagreement between theory and experiment was due to the large scatter and uncertainty of the experimental data or failure of the theory. However, there were very few instances of complete failure of the theory to explain experiment, and no one effect showed consistent disagreement, so that in general it may be said that the mechanisms of the second virial coefficients under study are reasonably well understood. It would require more precise measurements of the various effects, as well as more measured or calculated molecular property tensor components, such as the hyperpolarizability and the A- and C-tensors , to test the DID molecular interaction model more stringently. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1997.

Measurements of broadband electrostatic wave emIssons in conjunction with particle distributions in the earth's magnetosphere, have provided motivation for a number of studies of waves in plasmas with two electron components. One such wave-the electron-acoustic wave-arises when the two electron components have widely disparate temperatures (Watanabe & Taniuti 1977), and has a characteristic frequency that lies between the ion and electron plasma frequencies. Because of this broadband nature and because it is predominantly electrostatic, it provides a likely candidate for the explanation of the electrostatic component of "cusp auroral hiss" observed in the dayside polar cusp at between 2 and 4 earth radii as well as the broadband electrostatic noise (BEN) observed in the dayside polar regions and in the geomagnetic tail. The electron-acoustic wave and its properties provide the subjects for much of the investigation undertaken in this thesis. The thesis is divided into two parts. Part I is concerned with certain aspects of the linear theory of the electron-acoustic wave and is based on a kinetic description of the plasma. The dispersion relation for plane electrostatic waves obtained via linearisation of the Vlasov-Poisson system is studied in detail using analytical and numerical/geometrical techniques, and conditions under which the electron-acoustic wave arises are expounded. This work represents an extension of earlier works on Langmuir waves (Dell, Gledhill & Hellberg 1987) and the electron-acoustic wave (Gary & Tokar 1985). The effects of electron drifts and magnetization are investigated. These result, respectively, in a destabilization of the electron-acoustic wave and a modification of the dispersive properties. In this plasma configuration the model more closely replicates the conditions to be found in the terrestrial polar regions. We extend the parameter regimes considered in earlier works (Tokar &Gary 1984) and in addition, identify another electron sound branch related to the electron-cyclotron wave/instability. Effects of ion-beam destabilization of the electron-acoustic wave are also investigated briefly with a view to explaining BEN in the geomagnetic tail and also to provide a comparison with the electron-driven instability. In part II the nonlinear electron-acoustic wave is studied by employing a warm hydrodynamic model of the plasma components. We first consider weak nonlinearity and employ the asymptotic reductive perturbation technique of Washimi &Taniuti (1966) to render the hydrodynamical equations in the form of simpler evolutionary equations describing weakly-nonlinear electron-acoustic waves. These equations admit solitary-wave or soliton solutions which are studied in detail. Wherever possible we have justified our small amplitude results with full numerical integration of the original hydrodynamical equations. In so doing we extended the range of validity of our results to arbitrary wave amplitudes and also find some interesting features not directly predicted by the small amplitude wave equations. In this respect we were able to determine the important role played by the cool- to-hot electron temperature ratio for soliton existence. This important effect is in accordance with linear theory where the electron temperature ratio is found to be critical for electron-acoustic wave existence. The effects of magnetization on electron-acoustic soliton propagation is examined. We found that the magnetized electron-acoustic solitons are governed by a Korteweg-de Vries-Zakharov-Kusnetsov equation. In addition, it is shown that in very strong magnetic fields ion magnetization can become important yielding significant changes in the soliton characteristics. Multi-dimensional electron-acoustic solitons, which have greater stability than their plane counterparts, are also briefly discussed. Employing a weakly-relativistic hydrodynamic model of the plasma, the effect of a cool, relativistic electron beam on such soliton parameters as width, amplitude and speed is studied in detail. Both small- and large amplitude solitons are considered. The arbitrary-amplitude theory of Baboolal et al. (1988) is generalised to include relativistic streaming as well as relativistic thermal effects. The importance of the cool electron (beam)to- hot electron temperature in conjunction with the beam speed is pointed out. Finally, we derive a modified Korteweg-de Vries (mKdV) equation in an attempt to establish whether electron-acoustic double layers are admitted by our fluid model. Although double layers formally appear as stationary solutions to the mKdV equation, the parameter values required are prohibitive. This is borne out by the full fluid theory where no double layer solutions are found. / Thesis (Ph.D.)-University of Natal, Durban, 1991.

In this thesis, the dynamics and coupling in the middle atmosphere over the Southern Hemisphere are investigated using SuperDARN high frequency (HF) radar wind data, satellites, light detection and ranging (LIDAR), the South African National Antarctic Expedition (SANAE) imaging riometer and models. In particular, the study focuses on the unprecedented 2002 major stratospheric warming and its role in coupling the middle atmosphere. The dynamics of the middle atmosphere is investigated in terms of mean wind, temperature, gravity waves and planetary wave activity. Studying the middle atmospheric thermal structure over Southern Africa is an important activity to improve the understanding of atmospheric dynamics of this region. Observation of a middle atmosphere thermal structure over Durban (29.9 S, 31.0 E, South Africa) using LIDAR data collected from April 1999 to July 2004 (277 nights), including closest overpasses of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Halogen Occultation Experiments (HALOE) satellites, and the COSPAR International Reference Atmosphere (CIRA-86) are presented in this thesis. The observations from the LIDAR instrument, satellites and CIRA-86 exhibit the presence of annual oscillation in the stratosphere, whereas in the mesosphere the semi-annual oscillation seems to dominate the annual oscillation at some levels. The stratopause is observed in the height range of 40-55 km for all the instruments, with the stratopause temperatures being 260- 270 K for the LIDAR, 250-260 K for the SABER, and 250-270 K for the HALOE. Data from the LIDAR, satellites and CIRA-86 model indicate almost the same thermal structure of the middle atmosphere over Durban. This indicates a good agreement between LIDAR, satellites and the CIRA-86 model. Mean wind and planetary waves are investigated on a climatological scale in this study. Mean wind observations from the SANAE SuperDARN HF radar are compared with observations from Halley SuperDARN HF radar. There is a good agreement between the observations from the two stations both in the zonal and meridional wind components. Zonal wind is observed to be consistently larger than the meridional wind. The zonal wind is also consistently more eastward at both stations with maxima occurring during the solstice months. High latitude summer zonal mean ow at 94 km is observed to be weaker and more variable compared to the eastward winter mean circulation owing to tropospherically forced planetary waves propagating through the middle atmosphere. The zonal mean wind shows greater seasonal variability than does the meridional mean wind. This seasonal behaviour is reasonably well understood in terms of the upward propagating planetary waves and gravity waves interacting with the mean ow. The Coriolis force also plays an important role in the case of meridional wind component. The climatology of planetary waves both in the zonal and meridional wind components indicates an ampli cation of planetary waves of shorter wavenumbers (s = 3) in the winter months. During summer, long period oscillations (e.g. >10 days) which are dominant in winter disappear, and oscillations with shorter period (e.g. <10 days) become dominant. vi There is a strong planetary wave coupling between the stratosphere and mesosphere-lower thermospheric (MLT) during the year 2002 winter season, whilst the coupling is observed to be relatively weak during the other years. The strong planetary wave coupling in 2002 is understandable because during this year the middle atmosphere winter months were characterised by strong planetary wave activity which led to the rst ever detection of the SSW in the Southern Hemisphere. In the year 2002 winter period the mean circulation in the stratosphere is characterized by a series of planetary wave events that weakened the polar vortex and triggered the sudden stratospheric warming in late September. In particular, in the stratosphere there is a presence of a quasi 10-day eastward propagating planetary wave of wavenumber s=1, while in the MLT a quasi 14-day eastward propagating planetary wave of wavenumber s=1 is observed to be dominant. The Eliassen Palm ux (E-P) ux shows that strong planetary wave activity observed in the middle atmosphere originates from the troposphere. Zonal winds at the MLT show reversal approximately 7 days before the reversal at stratosphere, indicating a downwards propagation of circulation disturbance in the middle atmosphere. Eastward zonal winds dominate the winter MLT, but during the 2002 winter there are many periods of westward winds observed compared to the other years. The SABER vertical temperature pro les indicate cooling of the MLT region during the SSW occurrence. Gravity wave horizontal phase velocities and horizontal wavelengths as seen by the SANAE imaging riometer are observed to reduce dramatically over SANAE during the occurrence of the stratospheric warming. The disturbance of the middle atmosphere during the Southern Hemisphere stratospheric warming in year 2002 winter preconditioned the region for gravity waves to propagate upward to the MLT. The potential energy of these gravity waves is observed to increase with height up until they reach the lower thermosphere. At the MLT they lose their energy, thus depositing their momentum, leading to the MLT cooling and mean wind reversal. Keywords: SSW, Planetary waves, Gravity waves, Stratosphere, MLT, SuperDARN radar, Mean wind, Temperature, Middle atmosphere, SANAE. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

In this thesis we study spherically symmetric spacetimes which are static with a perfect fluid source. The Einstein field equations, in a number of equivalent forms, are derived in detail. The physical properties of a relativistic star are briefly reviewed. We specify two particular choices for one of the gravitational potentials. The behaviour of the remaining gravitational potential is governed by a second order differential equation. This equation has solutions in terms of elementary functions for some cases. The differential equation, in other cases, may be expressed as Bessel, confluent hypergeometric and hypergeometric equations. In such instances the solution is given in terms of special functions. A number of solutions to the Einstein field equations are generated. We believe that these solutions may be used to model realistic stars. Many of the solutions found are new and have not been published previously. In some cases our solutions are generalisations of cases considered previously. For some choices of the gravitational potential our solutions are equivalent to well-known results documented in the literature; in these cases we explicitly relate our solutions to those published previously. We have utilised the computer package MATHEMATICA Version 2.0 (Wolfram 1991) to assist with calculations, and to produce figures to describe the gravitational field. In addition, we briefly investigate the approach of specifying an equation of state relating the energy density and the pressure. The solution of the Einstein field equations, for a linear equation of state, is reduced to integrating Abel's equation of the second kind. / Thesis (M.Sc.)-University of Natal, Durban, 1993.