This thesis concerns the study of Ultra Low Frequency (ULF) waves during magnetospheric substorms. A wavelet algorithm which characterises magnetic ULF waves during substorm onset is presented. The algorithm is validated by comparing the spatial and temporal location of ULF wave onset to space-based observations of the aurora. It is demonstrated that the onset of ULF wave power expands coherently away from an ionospheric epicentre during the substorm expansion phase. Further, a case study of the time-domain causality of magnetotail plasma flows and ULF wave Pi2 pulsations is presented. Although highly correlated, it is demonstrated that the plasma flows cannot directly drive the ground magnetic waveforms but may be indirectly linked via a common source. Finally, results from a statistical study of ULF wave power during onset are presented. It is concluded that there is no statistical difference between historical sub-classifications of ULF waves observed during substorms.

No description available.

In recent years, many alternative models of the substorm process have been proposed to explain different aspects of this magnetospheric phenomenon. Some features in these competing models are compatible while others, such as the nature and location of substorm onset, remain controversial. The objective of this thesis is to assess the viability of the ballooning instability as a mechanism for initiating substorms. A review of the history and development of magnetospheric substorm research as well as a review of substorm models is presented. In these models, the crosstail current disruption responsible for the onset of the expansion phase is usually ascribed to the onset of some microinstability. An alternative triggering mechanism is a macroscopic magnetohydrodynamic instability such as the ballooning instability. To derive a threshold condition for the ballooning instability, a simplified magnetotail geometry with cylindrical symmetry near the equatorial plane is assumed. In such circumstances, the torsion of the magnetic field lines is zero and they can be characterised by their curvature. The hydromagnetic equations with isotropic pressure are linearised to find the dispersion relation. This leads to a threshold condition which depends on the pressure and magnetic field intensity gradients. In order to obtain realistic numerical results for the threshold condition, a quasistatic, self-consistent, two-dimensional numerical model of the magnetotail during conditions typical of substorm growth phase is used. The model involves solving the Grad-Shafranov equation with appropriate boundary conditions. It provides time-dependent magnetospheric magnetic field configurations that are characterised by the development of a minimum in Bz in the equatorial plane. Calculations of the detailed configuration of the magnetotail during onset allow an estimate of the instability criterion. In a model which does not allow an increase of pressure with radius, it is found that the magnetotail is not unstable to ballooning. Part of this work has been presented at a conference, viz.: Dormer, L.A. and A.D.M. Walker, Investigation of local MHD instabilities in the magnetotail using a two-dimensional magnetospheric convection model. Poster presented at the 39th annual South African Institute of Physics conference, University of Bophuthatswana, 1994. / Thesis (M.Sc.)-University of Natal, 1995.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Electrical Engineering In the Faculty of Engineering at the Cape Peninsula University of Technology, 2013 / The French South African Institute of Technology (F’SATI) at the Cape Peninsula University of Technology (CPUT) began a program in Satellite Systems Engineering in 2009 and is developing its first satellites. The satellites are based on the CubeSat standard, which defines one unit (1U) as a cube with a maximum weight of 1 kg and volume of 1dm3, and can be scaled up to three units (3U) for increased functionality. ZACUBE-1, a 1U CubeSat that is being developed, will be launched into a sun synchronous orbit in 2013. The main payload of the 1U CubeSat under development is a space weather experiment (beacon transmitter). The beacon transmitter is a scientific payload, which is being developed in collaboration with SANSA Space Science (SANSA SS) in Hermanus, South Africa. The beacon signal will be used to characterise the space weather radar antenna array at the South African National Antarctic Expedition (SANAE IV) base in Antarctica. The SANAE IV radar forms part of the SuperDARN (Dual Auroral Radar Network) project. This phased array antenna network comprises 16 radiating elements, with a 3o beam width that can be steered in 16 different directions to span the azimuth sector. These antennas are spread over both the northern and southern hemispheres. They operate in the HF band between 8 to 20 MHz and are used to primarily monitor the convection of the Earth’s magnetic field by monitoring coherent scatter from it. Orbital analyses were conducted to determine how the choice of the orbit affects the coverage of the array’s field-of-view. Propagation analyses were conducted to investigate how space weather variations affect HF signal propagation. The beacon signal will be used as an active target source and will enable the determination of the phase response of the array, thereby determining the direction-of-arrival of the signal. This will allow the experimental verification of the antenna’s beam pattern. The beacon signal prototype board was developed by using an RFID transceiver that operates in the HF band, capable of delivering up to 200 mW. Position determination of the satellite will be done by using two line elements (TLE) data. Experimental data will be available once ZACUBE-1 is in orbit; therefore, the work presented here documents a feasibility study and design of the experiment that will be conducted once the satellite is in orbit.

The functional linear model, $Y_n = Psi X_n + varepsilon_n$, with functional response and explanatory variables is considered. A simple test of the nullity of $Psi$ based on the principal component decomposition is proposed. The test statistic has asymptotic chi-squared distribution, which is also an excellent approximation in finite samples. The methodology is applied to data from terrestrial magnetic observatories. In recent years, the interaction of the auroral substorms with the equatorial and mid-latitude currents has been the subject of extensive research. We introduce a new statistical technique that allows us to test at a specified significance level whether such a dependence exists, and how long it persists. This quantitative statistical technique, relying on the concepts and tools of functional data analysis, uses directly magnetometer records in one minute resolution, and it can be applied to similar geophysical data which can be represented as daily curves. It is conceptually similar to testing the nullity of the slope in the straight line regression, but both the regressors and the responses are curves rather than points. When the regressors are daily high latitude $H$--component curves during substorm days and the responses are daily mid-- or low latitude $H$--component curves, our test shows significant dependence (the nullity hypothesis is rejected), which exists not only on the same UT day, but also extends into the next day for strong substorms. We propose a novel approach based on wavelet and functional principal component analysis to produce a cleaner index of the intensity of the symmetric ring current. We use functional canonical correlations to show that the new approach more effectively extracts symmetric global features. The main result of our work is the construction of a new index, which is an improved version of the existing wavelet-based index (WISA) and the old Dst index, in which a constant daily variation is removed. Here, we address the fact that the daily component varies from day to day and construct a ``cleaner'' index by removing non-constant daily variations. A wavelet-based method of deconvoluting the solar quiet variation from the low and mid-latitude H-component records is proposed. The resulting daily variation is non--constant, and its day--to--day variability is quantified by functional principal component scores. The procedure removes the signature of an enhanced ring current by comparing the scores at different stations. The method is fully algorithmic and is implemented in the statistical software R. R package for space physics applications is developed. It consists of several functions that compute indices of the storm activity and estimate the daily variation. Storm indices are computed automatically without any human intervention using the most recent magnetometer data available. Functional principal component analysis techniques are used to extract day-to-day variations. This package will be publicly available at Comprehensive R Archive Network (CRAN).

Les recherches décrites dans ces pages portent sur l'étude de l'aurore à protons par télédétection spatiale en ultraviolet lointain. Ce travail s'inscrit dans le cadre de la mission IMAGE, dont l'instrument FUV offre la possibilité d'observer les émissions aurorales dues à la précipitation d'électrons et de protons. L'imageur spectral SI12, construit au Centre Spatial de Liège, donne une image de la raie Lyman-alpha déplacée par effet Doppler produite par la désexcitation de l'hydrogène. Il permet l'observation globale de l'ovale auroral avec une résolution temporelle de 2 minutes. Les données couplées à un modèle de transport et de dégradation d'énergie des particules qui précipitent ont été utilisées pour étudier l'aurore à protons tant d'un point de vue morphologique que d'un point de vue quantitatif. La première étape du travail consistait à valider les observations et à calibrer la méthode développée pour obtenir les flux énergétiques des particules accélérées vers l'atmosphère à partir des taux de comptage SI12. Des comparaisons des observations SI12 et des mesures in situ de particules des satellites NOAA ont montré un désaccord de 50%, qui a été pris en considération dans la suite du travail. J'ai ensuite entrepris une étude statistique des caractéristiques morphologiques de l'ovale protonique. Cette statistique présente un très bon accord avec les études précédentes, bien que celles-ci soient basées sur des mesures locales de la précipitation de protons. Les résultats quantitatifs quant à l'intensité de la précipitation des protons ont montré une variation saisonnière, avec un maximum dans l'hémisphère estival. J'ai également mis en évidence l'influence de l'orientation de la composante nord/sud du champ magnétique interplanétaire et de la pression dynamique du vent solaire sur la précipitation de protons tant au point de vue de l'énergie accumulée durant la phase de croissance, que des processus de déclenchement de leur précipitation et des processus de précipitation eux-mêmes. L'analyse de la dynamique de l'ovale auroral protonique durant les phases de croissance des sous-tempêtes magnétiques a montré que le mouvement vers l'équateur des frontières de l'ovale pouvait être local, global ou une superposition des deux. Ce résultat est interprété comme la combinaison d'un étirement global de la magnétosphère dû à l'influence du vent solaire et d'un étirement local trouvant son origine dans le feuillet de plasma interne à la magnétosphère. Dans la dernière étape du travail, j'ai analysé les conséquences de la précipitation aurorale sur l'ionosphère. J'ai montré que les conductivités de Hall et de Pedersen et leur évolution temporelle pouvaient être déduites de la contribution des trois imageurs ultraviolets à une échelle spatiale globale. Le résultat principal de cette partie montre que la contribution des protons à la puissance et aux conductances aurorales ne peut localement pas être négligée par rapport à celle des électrons.

Solar transient eruptions are the main cause of interplanetary-magnetospheric disturbances leading to the phenomena known as geomagnetic storms. Eruptive solar events such as coronal mass ejections (CMEs) are currently considered the main cause of geomagnetic storms (GMS). GMS are strong perturbations of the Earth’s magnetic field that can affect space-borne and ground-based technological systems. The solar-terrestrial impact on modern technological systems is commonly known as Space Weather. Part of the research study described in this thesis was to investigate and establish a relationship between GMS (periods with Dst ≤ −50 nT) and their associated solar and interplanetary (IP) properties during solar cycle (SC) 23. Solar and IP geoeffective properties associated with or without CMEs were investigated and used to qualitatively characterise both intense and moderate storms. The results of this analysis specifically provide an estimate of the main sources of GMS during an average 11-year solar activity period. This study indicates that during SC 23, the majority of intense GMS (83%) were associated with CMEs, while the non-associated CME storms were dominant among moderate storms. GMS phenomena are the result of a complex and non-linear chaotic system involving the Sun, the IP medium, the magnetosphere and ionosphere, which make the prediction of these phenomena challenging. This thesis also explored the predictability of both the occurrence and strength of GMS. Due to their nonlinear driving mechanisms, the prediction of GMS was attempted by the use of neural network (NN) techniques, known for their non-linear modelling capabilities. To predict the occurrence of storms, a combination of solar and IP parameters were used as inputs in the NN model that proved to predict the occurrence of GMS with a probability of 87%. Using the solar wind (SW) and IP magnetic field (IMF) parameters, a separate NN-based model was developed to predict the storm-time strength as measured by the global Dst and ap geomagnetic indices, as well as by the locally measured K-index. The performance of the models was tested on data sets which were not part of the NN training process. The results obtained indicate that NN models provide a reliable alternative method for empirically predicting the occurrence and strength of GMS on the basis of solar and IP parameters. The demonstrated ability to predict the geoeffectiveness of solar and IP transient events is a key step in the goal towards improving space weather modelling and prediction.

<p>Magnetized planets, such as Earth, are strongly influenced by the solar wind. The Sun is very dynamic, releasing varying amounts of energy, resulting in a fluctuating energy and momentum exchange between the solar wind and planetary magnetospheres. The efficiency of this coupling is thought to be controlled by magnetic reconnection occurring at the boundary between solar wind and planetary magnetic fields. One of the main tasks in space physics research is to increase the understanding of this coupling between the Sun and other solar system bodies. Perhaps the most important aspect regards the transfer of energy from the solar wind to the terrestrial magnetosphere as this is the main source for driving plasma processes in the magnetosphere-ionosphere system. This may also have a direct practical influence on our life here on Earth as it is responsible for Space Weather effects. In this thesis I investigate both the global scale of the varying solar-terrestrial coupling and local phenomena in more detail. I use mainly the European Space Agency Cluster mission which provide unprecedented three-dimensional observations via its formation of four identical spacecraft. The Cluster data are complimented with observations from a broad range of instruments both onboard spacecraft and from groundbased magnetometers and radars.</p><p>A period of very strong solar driving in late October 2003 is investigated. We show that some of the strongest substorms in the history of magnetic recordings were triggered by pressure pulses impacting a quasi-stable magnetosphere. We make for the first time direct estimates of the local energy flow into the magnetotail using Cluster measurements. Observational estimates suggest a good energy balance between the magnetosphere-ionosphere system while empirical proxies seem to suffer from over/under estimations during such extreme conditions.</p><p>Another period of extreme interplanetary conditions give rise to accelerated flows along the magnetopause which could account for an enhanced energy coupling between the solar wind and the magnetosphere. We discuss whether such conditions could explain the simultaneous observation of a large auroral spiral across the polar cap.</p><p>Contrary to extreme conditions the energy conversion across the dayside magnetopause has been estimated during an extended period of steady interplanetary conditions. A new method to determine the rate at which reconnection occurs is described that utilizes the magnitude of the local energy conversion from Cluster. The observations show a varying reconnection rate which support the previous interpretation that reconnection is continuous but its rate is modulated.</p><p>Finally, we compare local energy estimates from Cluster with a global magnetohydrodynamic simulation. The results show that the observations are reliably reproduced by the model and may be used to validate and scale global magnetohydrodynamic models.</p>

Magnetized planets, such as Earth, are strongly influenced by the solar wind. The Sun is very dynamic, releasing varying amounts of energy, resulting in a fluctuating energy and momentum exchange between the solar wind and planetary magnetospheres. The efficiency of this coupling is thought to be controlled by magnetic reconnection occurring at the boundary between solar wind and planetary magnetic fields. One of the main tasks in space physics research is to increase the understanding of this coupling between the Sun and other solar system bodies. Perhaps the most important aspect regards the transfer of energy from the solar wind to the terrestrial magnetosphere as this is the main source for driving plasma processes in the magnetosphere-ionosphere system. This may also have a direct practical influence on our life here on Earth as it is responsible for Space Weather effects. In this thesis I investigate both the global scale of the varying solar-terrestrial coupling and local phenomena in more detail. I use mainly the European Space Agency Cluster mission which provide unprecedented three-dimensional observations via its formation of four identical spacecraft. The Cluster data are complimented with observations from a broad range of instruments both onboard spacecraft and from groundbased magnetometers and radars. A period of very strong solar driving in late October 2003 is investigated. We show that some of the strongest substorms in the history of magnetic recordings were triggered by pressure pulses impacting a quasi-stable magnetosphere. We make for the first time direct estimates of the local energy flow into the magnetotail using Cluster measurements. Observational estimates suggest a good energy balance between the magnetosphere-ionosphere system while empirical proxies seem to suffer from over/under estimations during such extreme conditions. Another period of extreme interplanetary conditions give rise to accelerated flows along the magnetopause which could account for an enhanced energy coupling between the solar wind and the magnetosphere. We discuss whether such conditions could explain the simultaneous observation of a large auroral spiral across the polar cap. Contrary to extreme conditions the energy conversion across the dayside magnetopause has been estimated during an extended period of steady interplanetary conditions. A new method to determine the rate at which reconnection occurs is described that utilizes the magnitude of the local energy conversion from Cluster. The observations show a varying reconnection rate which support the previous interpretation that reconnection is continuous but its rate is modulated. Finally, we compare local energy estimates from Cluster with a global magnetohydrodynamic simulation. The results show that the observations are reliably reproduced by the model and may be used to validate and scale global magnetohydrodynamic models.

The goal of this thesis is to improve our knowledge on energetic particle precipitation into the Earth’s atmosphere from the thermosphere to the surface. The particles origin from the Sun or from temporarily trapped populations inside the magnetosphere. The best documented influence of solar (high-) energetic particles on the atmosphere is the Ozone depletion in high latitudes, attributed to the generation of HOx and NOx by precipitating particles (Crutzen et al., 1975; Solomon et al., 1981; Reid et al., 1991). In addition Callis et al. (1996b, 2001) and Randall et al. (2005, 2006) point out the importance of low-energetic precipitating particles of magnetospheric origin, creating NOx in the lower thermosphere, which may be transported downwards where it also contributes to Ozone depletion. The incoming particle flux is dramatically changing as a function of auroral/geomagnetical activity and in particular during solar particle events. As a result, the degree of ionization and the chemical composition of the atmosphere are substantially affected by the state of the Sun. Therefore the direct energetic or dynamical influences of ions on the upper atmosphere depend on solar variability at different time scales. Influences on chemistry have been considered so far with simplified precipitation patterns, limited energy range and restrictions to certain particle species, see e.g. Jackman et al. (2000); Sinnhuber et al. (2003b, for solar energetic protons and no spatial differentiation), and Callis et al. (1996b, 2001, for magnetospheric electrons only). A comprehensive atmospheric ionization model with spatially resolved particle precipitation including a wide energy range and all main particle species as well as a dynamic magnetosphere was missing. In the scope of this work, a 3-D precipitation model of solar and magnetospheric particles has been developed. Temporal as well as spatial ionization patterns will be discussed. Apart from that, the ionization data are used in different climate models, allowing (a) simulations of NOx and HOx formation and transport, (b) comparisons to incoherent scatter radar measurements and (c) inter-comparison of the chemistry part in different models and comparison of model results to MIPAS observations. In a bigger scope the ionization data may be used to better constrain the natural sources of climate change or consequences for atmospheric dynamics due to local temperature changes by precipitating particles and their implications for chemistry. Thus the influence of precipitating energetic particles on the composition and dynamics of the atmosphere is a challenging issue in climate modeling. The ionization data is available online and can be adopted automatically to any user specific model grid.