Bibliography: pages 113-119. / Field and theoretical investigations were made of the nearshore circulation of Matroos Bay, a small embayment on the south-western coast of Africa. The field study revealed two dominant circulation types, denoted "anticlockwise" and "clockwise". The anticlockwise circulation type was characterized by longshore currents flowing from the back of the bay to the northern headland where a rip current was located. The clockwise circulation type was characterized by longshore currents flowing from the northern headland to the back of the bay where a rip current was situated. Anticlockwise circulation types were primarily found to occur during periods of low waves, the clockwise circulation during periods of high waves. Winds and coastal currents were found not to have a major influence on the circulation within the bay. The theoretical study was based on a model of longshore currents in a semi-circular bay (O'Rourke and Le Blond, 1972). This study showed that a change of the height of the wave could lead to a change in the direction of flow of the longshore current. In agreement with the field study, a low wave height was found to result in an anticlockwise circulation type, a high wave height resulting in a clockwise circulation type. The change from one circulation type to the other depended on the relative strength of two opposing mechanisms. One mechanism arose from the obliquity of the wave approach to the shore. This mechanism generated longshore currents towards the back of the bay and was dominant during high waves. The other mechanism resulted from the non-uniformity of the wave height around the bay and generated longshore currents flowing from the back of the bay. Coastal currents were measured as part of the field study. A fair correlation was-observed between the direction of the coastal current and that of the wind, particularly if the winds were moderate to strong. Temperature and salinity measurements were also made. These properties showed seasonal variations in accord with the principles of upwelling. Surface water was found to have a salinity similar to that found at a depth of 400 to 600 metres in the South Atlantic Ocean. The water was upwelled from a greater depth during the summer than during the winter. Heating of the water was found to be greater in summer than in winter whilst dilution of the water, due to rainfall, was found to be negligible, even during winter. The interchange of water between the bay and the coastal circulation was found to be dependent on the circulation type.

Includes bibliographical references (leaves 94-111). / The mesoscale structure of the low-level wind field associated with a strong upwelling event was investigated. During July 2005 when a strong upwelling event occurred, the Somali jet was found to have oscillated at lower frequency of 3-7 weeks than the normal bi-weekly mode observed in several studies and the mesoscale winds exhibited high covariability with the prevailing SSTs. Strong values of alongshore winds were deduced from late June to mid-July. These winds weakened significantly in the third and fourth week of July. A large off-shore pressure gradient due to differential thermal properties of land and sea was also observed.

Bibliography: pages 108-112. / A first detailed picture of the Agulhas current is obtained from data of the Quasi synoptic Agulhas current cruise of March 1969. Reinterpretation of other hydrographic data was possible in the light of the 1969 cruise and the information obtained from satellite tracked buoys. For the 1969 cruise acceleration potential diagrams on various sigma-t levels are discussed and indicate that certain features in the current are of such a scale (length and time) that only closely spaced synoptic stations will show them. Of special interest are the following features: two main supplies to the current; a region of dynamical upwelling between East London and Port Elizabeth; the region where the current turns eastward (retroflection); the interaction with the South East Atlantic ocean; the planetary waves in the Agulhas return current over and east of the Agulhas plateau.

Introduction: Intracranial pressure (ICP) monitoring is a cornerstone of care for patients with severe traumatic brain injury (TBI). The primary goal of ICP treatment is to preserve brain oxygenation, and since brain oxygenation is usually not measured, the control of ICP is used as a surrogate marker. However studies indicating that cerebral hypoxia/ischemia may occur in the face of adequate ICP and cerebral perfusion pressure (CPP) suggest that the interaction between ICP and brain oxygenation is poorly understood and warrants further investigation. This is of particular importance in the context of children in whom the interpretation of relationships between intracranial factors is even more complex due to changing physiological norms with age. To date little scientific data exists in children and treatment threshold values are often extrapolated from adult guidelines. This study aims to better understand the relationship between ICP and brain oxygenation measured as brain tissue oxygen tension (PbtO2) in a large paediatric cohort suffering from severe TBI. Specifically analysis 1) investigated ICP and PbtO2 profiles over time following TBI, 2) examined the relationship between ICP and PbtO2 from time-linked paired observations, 3) explored various critical thresholds for ICP and PbtO2, and 4) interrogated digital data trends depicting the relationship between ICP and PbtO2. The level of agreement between hourly recorded and high frequency electronic data for ICP and PbtO2 was also evaluated. Method: Paired ICP and PbtO2 data from 75 children with severe TBI were tested with correlation and regression. Additional analyses controlled for mean arterial pressure (MAP), arterial partial pressure of oxygen (PaO2), CPP, arterial partial pressure of carbon dioxide (PaCO2) and haemoglobin (Hb) using multivariate logistic regression analysis and general estimating equations. Various thresholds for ICP were examined; these included age-related thresholds to account for the potential influence of age. Receiver-operating curves (ROCs) were used to graphically demonstrate the relationships between various thresholds of ICP and various definitions of low PbtO2. These were constructed for pooled and individual patient data. Interrogation of electronically recorded data allowed for case illustrations examining the relationship between ICP and PbtO2 at selected time points. Hourly and electronic data were compared using Bland and Altman plots and by contrasting the frequency of ICP and PbtO2 perturbations recorded with each system. 5 Result: Analyses using over 8300 hours of paired observations revealed a weak relationship between ICP and PbtO2, with an initially positive but weak slope (r = 0.05) that trended downwards only at higher values of ICP. Controlling for inter-individual differences, as well as MAP, CPP, PaO2, PaCO2 and Hb did not strengthen this association. This poor relationship was further reflected in the examination of threshold ICP values with ROCs, no singular critical ICP threshold for compromised brain oxygenation was discernible. Using age-based thresholds did not improve this relationship and individual patient ROCs demonstrated inter-individual heterogeneity in the relationship between ICP and PbtO2. However, it was clear that in individual patients ICP did exhibit a strong negative relationship with PbtO2 at particular time points, but various different relationships between the 2 variables were also demonstrated. A high level of agreement was found between hourly and electronic data. Conclusion: These results suggest that the relationship between ICP and PbtO2 is highly complex. Although the relationship in individual children at specific time points may be strong, pooled data for the entire cohort of patients, and even for individual patients, suggest only a weak relationship. This is likely because several other factors affect PbtO2 outside of ICP, and some factors affect both independently of each other. These results suggest that more study should be directed at optimising ICP thresholds for treatment in children. The use of complimentary monitoring modalities may assist in this task. Depending on the adequacy of measures of brain perfusion, metabolism or oxygenation, it is possible that targeting a range of ICP values in individual patients may be appropriate; however this would require detailed investigation.

Sea surface temperatures in the tropical Indian Ocean have been shown to be inversely related to South African summer rainfall, making advanced predictions of this rainfall practicable. Such predictability has enormous potential economic benefits. However, these predictions have been purely statistical; very little is currently known about the marine-atmospheric processes in the Indian Ocean tropics. To address this lack of information, the structure of the upper ocean and lower atmosphere as well as the surface heat fluxes in the tropical Indian Ocean have been investigated. This was done by a special measurement programme on a research cruise in the region. Global gridded meteorological data have been used to complement the shipboard observations. Heat fluxes have been computed from the cruise observations and related to the main atmospheric patterns at the time. These patterns were identified from principal components analysis. Air-sea interaction could thus be estimated over the full tropical Indian Ocean. It is found that the thermocline depth is linked to the cyclonic ocean current shear and to the overlying distribution of wind stress curl. The meridional advection of air into the central Indian Ocean region is shown to modulate the characteristics of the atmospheric boundary layer in the tropical Indian Ocean. The maximum turbulent heat and moisture transports to the atmosphere are found near cyclonic atmospheric disturbances. These are the first reliable observations of the heat and moisture fluxes in that part of the tropical Indian Ocean implicated in South African rainfall. It is clear from this investigation that the synoptic atmospheric systems and the meridional flow of air are critical to enhanced atmospheric convection in the region.

In this thesis the applicability of ocean environment modelling as a part of optimal naval operational efficiency, and thus military oceanography, is evaluated. To be able to do this, the principles of knowledge-based warfare and the ability to make rapid environmental assessments, are introduced. These then form part of optimal efficiency. Modelling of the environment implies knowledge-based warfare and accommodates the ability to make a rapid environmental assessment. After an overview of past and current ocean modelling (specifically wave modelling), the third generation SWAN (Simulating WAves Nearshore) model is selected to model a small component of the military oceanographic spectrum viz. waves. The selected area, includes an area where the US Navy conducted an amphibious landing exercise (Operation Laurel) during October 2001. Three case studies are considered for modelling. These included an extreme wave condition, a mode wave condition and the conditions during Operation Laurel. Data were obtained from the wave rider buoy at Slangkop near Cape Town and analysed for a specific period during 2001. In all three cases the wave dissipation and maximum energy transfer areas were determined from the model. From these, certain deductions could be made regarding the influence the environment under these three different conditions could have on naval operations in the littorals. It is concluded that ocean modelling should form an integral part of naval operational efficiency and its contribution as force multiplier should be taken into consideration.

The southwest continental shelf of Africa is characterized by a strong western boundary current with three interdependent components, namely the Agulhas Current, Agulhas Retroflection and Agulhas Return Current. This system plays a key role in setting oceanic conditions south of Africa. The Crossroad transect intersects both the Agulhas Current and Agulhas Return Current; a monitoring line established in 2013 to sample both the currents and determine inter-ocean fluxes, as well as the influence of the Agulhas Current on the Agulhas Bank shelf. The objective of the study was to examine both mesoscale and submesoscale features that influence the dynamic and variant nature of the Agulhas system. In this study we make use of Ship board Acoustic Doppler Current Profiler (SADCP), Conductivity Temperature and Depth (CTD), Thermosalinograph (TSG) and satellite Sea Surface Height data as main observations for analysis. The study also examines both the spatial and temporal characteristics of water properties across the Crossroad transect. The fundamental findings of the study include the abundance of both the mesoscale and submesoscale features observed in the Agulhas system, which are often overlooked. In addition, a noticeable variability in current measurements was observed, where velocity ranging from 2 to 2.5 m/s represented the Agulhas Current and 1.4 to 1.7 m/s, Agulhas Return Current. The position of the Agulhas Current and Agulhas Return Current displayed variation from 2013 to 2015, with the Agulhas Return Current exhibiting a meandering pattern in 2014 along the transect. Furthermore, an intrusion of cool (8 to 13 °C), lower salinity (34.8 to 35 psu) South Indian Central Water masses were also observed along the Agulhas Bank. The ability to combine altimetry and in situ data also contributed to the analysis of the results. Therefore, given the inherent advantage of satellite and in situ measurements, an overview of the variability across the Crossroad transect was determined.

The structure and variability of inter-annual and intra-seasonal circulation anomalies and their precursors are investigated over northern Tanzania. Area rainfall departures are computed in the period 1960-1990 and wet and dry years are identified. Northern Tanzania experiences bimodal rains centred on the seasons: March to May (Masika) and October to December (Vuli). Station inter-correlations in Masika are of order +0.4, whereas in Vuli correlations are of order+0.7. Using composite sequences of gridded sea surface temperatures (SST),outgoing longwave radiation (OLR) and winds in the lower- and upper troposphere, the- precursors of flood and drought are assessed. Composites are averaged for the specific season and for periods 2, 4 and 6 months prior; and the historical mean is subtracted to produce anomalies. In this way, evolution of extreme rainfall scenarios is tracked for predictive purposes. The patterns analysed show that when positive SST anomalies persist in the Indian Ocean, sympathetic negative OLR values and local rainfall enhancement are observed. Using pentad (5 day mean) rainfall time series for the area, wet spells are analysed for structure and evolution. ECMWF data for the peak in Vuli rainfall each year from 1986 to 1991 are averaged to form a single composite. The historical mean is subtracted from the composite to produce anomalies for the wet spell and the preceeding pentads.

Bibliography: leaves 110-120. / Hydrographic sections between Africa and Antarctica; the A12, SR02 and SR02 sections conducted in 1990, 1990 and 1993 are presented here in comparison with the AJAX section of 1984. The numbered sections were undertaken as part of WOCE to better understand the ocean and the role it plays in the distribution of heat, salt, oxygen and nutrients south of Africa. In this study the focus was put on the SR02 section done in 1993 by South African scientists. The three sections also provided for a fresh look at the spatial and temporal variability of the hydrographic environment along the Greenwich Meridian.

Includes bibliographical references. / The currents, winds and hydrology of a coastal site of approximately 120 square miles off South West Africa were studied intensively for two weeks during June/July 1978. Currents were measured by means of drogues tracked by RADAR from a central station at 45m of water depth. Classical inertial motion was observed at several depths during a calm period implying a short relaxation time for pressure gradient forces and the existence of different Velocity layers within the water column. Diurnal sea breezes and landbreezes controlled the currents at 2 and 5m depth with a response time of a few hours but the deeper currents were not directly affected by wind. Average surface current speeds were between 0,2 and 0,3 kts. Sustained southerly winds caused a deepending of the upper layer and were accompanied ~y slower currehts. Selected data recorded during the diurnal wind regime yielded the relationship: Surface current speed = 0,017 x Windspeed. A meandering poleward under-current with an average velocity of 0,07 kts was detected at 30m depth whilst onshore flow of similar average speed existed at 20m. Using the results of the experimental work as a basis, the upper layer of the sea to 8m depth was modelled as a slab, which was affected by wind, friction and the coriolis force.