Browsing by Subject "Physical Oceanography"

Now showing 1 - 16 of 16
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    Cyclonic Eddies in the Cape Basin
    (2008) Hall, C; Lutjeharms, Johann R E
    A great deal of attention has been paid to the inter-ocean exchange of thermohalineproperties in the Agulhas Retroflection region. Recent observations have shown thatthe highly energetic field of the southern half of the Cape Basin consists of bothcyclonic and anticyclonic eddies. These eddies interact with each other, resulting inthe vigorous stirring of these water mass. Investigations have shown that the cycloniceddies tend to be smaller and outnumber the anticyclonic rings. Nonetheless, verylittle is known of their characteristics and the nature in which they are formed. Usingremote sensing data, confirmed with hydrographic data, this study determines thelocation, frequency and seasonality of cyclonic eddy formation; their size, trajectoriesand lifespan; physical components and associations with Agulhas Rings.Cyclonic eddies were seen to split, merge and link with other cyclonic eddies, withsplitting events creating child cyclonic eddies. The 105 parent and 157 child cycloniceddies identified during this study show that an average of II parent and 17 childcyclonic eddies were formed annually. 31.58 % follow an overall west-southwestdirection, with 27.37 % translocating west north-westward. Poleward translocationspeeds average at 0.3 kIn/day, whereas translocation speeds obtained from alldirectional components averages at 2.153 kIn/day for parent and 2.975 km/day forchild cyclonic eddies. Parent cyclonic eddies lived for approximately 254 days,whereas child cyclonic eddies survived for a mean of 188 days. Of note was asignificant variation of lifespan between parent and child cyclonic eddies formed inboth the north and south of the study area. 77 % of northern and 93 % of southerncyclonic eddies were formed directly adjacent to positive sea level anomalies orAgulhas Rings, resulting in an total overall association of 82.93 % parent and 89.63 %child cyclonic eddies. Cyclonic eddy groups were seen to merge at a rate of 16.38parent and 14 child cyclonic eddies per year, whereas topography appeared to affectthe demise of 17.00 % of the investigated cyclonic eddies.Therefore this study may form a basis for further investigations into the influenceCape Basin cyclonic eddies have on the meridional transfer of heat, salt, nutrients,oxygen and carbon concentrations in the South-East Atlantic Ocean. A more in-depthstudy using model outputs and targeted in situ hydrographical data would againenhance cyclonic eddy knowledge.
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    A description of the seasonality and its variability in a numerical ocean model of the Southern Benguela Region
    (2004) Bergman, Selwyn; Shillington, Frank; Roy, Claude
    The Southern Benguela has, for various reasons, been a focal point for research particularly in recent years. One of the most notable reasons for this interest can he found in the presence of economically viable fish species and their relationship to the process of upwelling. A numerical model of the entire Southern Benguela Region has previously been set up in order to assist furlher studies in the region. This dissertation presents the use of the model in an investigation on the seasonality and the interannual variability in temperature, salinity and general circulation in the region. Hovmuller Plots of the climatology and the associated anomalies were calculated in order to determine the characteristics of the seasonal cycle. It also became possible to deduce a vertical structure of upwelling.
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    Drivers of coastal sea level variability along the east and south of South Africa
    (2019) Nhantumbo, Bernardino João; Shillington, Frank; Backeberg, Björn; Nilsen, Jan Even; Reason, Christopher
    Sea level rise and variability is of great concern in the coastal areas where a significant part of the global population is settled. Therefore, understanding regional and local long-term sea level variability as well as its trend is critical. On the other hand, quantifying how the sea level has varied on different timescales and why, is critical for understanding sea level changes, and crucial for improving future global, regional, and local projections. In this study, monthly mean sea level records of seven individual tide gauges, from the east and south coast of South Africa were used to analyse the embedded timescales of variability. These timescales were separated through the Empirical Mode Decomposition (EMD) method. This is the first time that the EMD method has been applied to southern African tide gauge records. The sensitivity of the EMD method when dealing with data gaps was tested on artificially created gaps in monthly mean synthetic altimetry sea level records, representing the seven individual tide gauges under consideration. The missing values were filled by linear interpolation, average value and linear trend value. The results suggested that whichever gap filling method is applied, the separated EMD timescales will display a distorted temporal structure of the continuous time series. As a consequence, monthly mean tide gauge sea level records were optimised by filling the gaps as best as possible using satellite altimetry data and the adjacent tide gauge records where possible, and then the oscillatory timescales of variability were separated using the EMD method with the intent to determine their physical drivers. However, identifying a single driver for each separated timescale is challenging due to our limited knowledge of how sea level is linked to the various forcing mechanisms. Therefore, the timescales of sea level variability extracted using the EMD were grouped into sub-annual and interannual timescales, and their relationship to possible driving mechanisms was investigated. The sub-annual timescale indicates how sea level responds to the mesoscale and synoptic weather systems in the annual cycle, including seasonal and annual large-scale wind and atmospheric pressure pattern changes. The interannual timescale indicates an association with the climate indices including El Niño-Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode through large-scale sea surface temperature patterns and large-scale pressure and wind patterns. In addition, the results have suggested that the studied coastal sea level has an association with the Agulhas Current at both sub-annual and interannual timescale through absolute dynamic topography variations at the Agulhas Current core locations. However, due to limitations in Agulhas Current data, the study was limited to East London and Port Elizabeth and the results suggested that the Agulhas Current contribution is responsible for over 62% of the monthly sea level variability at East London. However, the results were not sufficiently consistent to suggest a firm conclusion at Port Elizabeth.
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    Empirical dynamics of a small scale coastal upwelling region
    (1991) Bain, Cairns Alexander Robertson; Brundrit, Geoff B
    The study investigates the dynamics of a small space scale (less than 10 km) coastal upwelling region at the temporal scales spanning hours to years. Three to four year time series data sets of, sea temperatures at different depths (2m, 5 m and 8,5 m) one kilometer offshore, of wind and of waves, obtained from Eskom for the Koeberg nuclear power station site study near Melkbosstrand (33° 41'S, 18° 26'E) were digitized on an hourly basis. An emphasis is placed on the study of the wind and sea temperature data, the latter being an unique data set in the South African context. The data were filtered into different frequency bands (<12,0 <0,5 <0,025 cpd). Simple statistics, linear correlation and spectral analysis were used to characterize these bands. Dominant temporal scales were identified as the seasonal, event (synoptic) and diurnal time scales. The characterization of the latter two time scales were supplemented with field work which inter alia measured: sea temperature profiles and transects; sea surface temperature distribution with the airborne radiation thermometry technique and Lagrangian currents.
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    Impacts of ENSO on coastal South African sea surface temperatures
    (2020) Nhesvure, Belinda; Rouault, Mathieu
    The impact of El Niño Southern Oscillation (ENSO) on the Southern African inland climate is well documented and provides skill in the seasonal forecast of rainfall but little is known of the impact of ENSO on the ocean surrounding South Africa. The aim of this study is to assess the impact of ENSO on sea surface temperatures around the coast of South Africa and to calculate SST trends around the coast. I start by updating the study of Rouault et al (2010) on the very topic with an additional 10 years of data and two additional newer datasets which allow sampling closer to the coast where wind-driven upwelling is more active. The new highresolution ERA 5 reanalyzed climate dataset is also used to look at the atmospheric forcing of sea surface temperatures by ENSO. As in Rouault et al. (2010), I study five similar threedegree-long coastal regions around South Africa, namely: West Coast, South Coast, Port Elizabeth/Port Alfred, Transkei, Kwazulu-Natal and a larger offshore Agulhas Current area domain. Three SST datasets are evaluated in this study: the 1 ̊x1 ̊Optimal Interpolation sea surface temperature (OI SST) used by Rouault et al (2010), the 0.25 ̊x 0.25 ̊ Optimal Interpolation SST and the 4 km x 4 km Advanced Very High-Resolution Radiometer (AVHRR) Pathfinder SST version 5.3. The 0.25 ̊x 0.25 ̊OI SST resolvesSST anomalies better in these coastal regions as compared to 1 ̊x1 ̊ OISST. The difference in results among the three products concerning trends and correlation with ENSO is a cause for concern. The 4 km x 4 km AVHRR Pathfinder allows for SST to be extracted even closer to the coast but missing values are numerous and hamper the use of this dataset for ENSO composites and trend analyses. Results show a significant positive correlation with El Niño in summer at the monthly scale, reaching a maximum correlation of 0.45 at 3 months lag. Correlation is the highest in late summer. There is a negative correlation in the Agulhas Current area, opposite to those with ENSO and West Coast. The impact of ENSO on the coast of South Africa, West Coast and South Coast is due to change in surface wind speed with weaker upwelling favorable during El Niño leading to warmer than normal coastal water SST and stronger than normal Southeasterly winds during la Niña leading to cooler than normal coastal water. The wind perturbation is part of largescale basin-wide perturbations in the tropical Atlantic, in the South Atlantic high-pressure atmospheric system and in the westerly wind pattern of the midlatitude to the south. Non-ENSO related impact can be as important as ENSO related SST perturbation and is also linked to large scale perturbations in the South Atlantic. There is no relation between the strength of ENSO and the strength of the perturbation, and some ENSO events do not lead to the expected canonical warming or cooling. The large-scale SST perturbations seem to be caused by anomalous surface turbulent flux of latent and sensible heat and abnormal wind speed and direction. This study opens the possibility of seasonal forecasting of SST in the South Benguela upwelling system because of the positive lag correlation between ENSO and SST with ENSO leading SST.
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    Investigating the local circulation of the southeast Cape Basin
    (2018) Carr, Matthew David; Lamont, Tarron; Ansorge, Isabelle Jane
    Located off the west coast of southern Africa, the southeast Cape Basin is characterised by a unique combination of strong coastal upwelling and vigorous offshore mesoscale variability. The juxtaposition of offshore mesoscale variability and coastal upwelling results in a complex and dynamic environment. In this study a combination of in situ Acoustic Doppler Current Profiler (ADCP) data and satellite observations were used to identify, describe and characterise the features driving the local circulation within the southeast Cape Basin. The ADCP data was obtained from the South Atlantic MOC Basin-wide Array (SAMBA), which included four deep sea moorings located along ~34.5°S on the 1000, 2000, 3000 and 4500m isobaths respectively. There was a distinct difference in the circulation observed at the mooring located on the shelf edge (1000m) and the moorings further offshore (2000m, 3000m and 45000m). The offshore circulation, observed by the moorings located on the 2000, 3000, 4500m isobaths, were driven by large mesoscale eddies, both cyclonic and anticyclonic, originating at the Agulhas retroflection and within the Cape Basin itself. The mesoscale eddies induced high speed baroclinic transport events which impacted the upper water column to a depth of at least 400m. The in situ observations were used to show the precise characteristics of two cyclonic shelf eddies and one anticyclonic eddy through the upper water column (~50 to 500m). The analysis of these features was important as the physical characteristics of both the cyclonic shelf eddies and anticyclonic eddies through depth are not well known. Considering the short period of observations (18th September 2014 to 1st December 2015), the analysis was not used to assume the prevailing physical characteristics of cyclonic shelf eddies and anticyclonic eddies. Instead the analysis showed the potential for future long term studies to use the sustained in situ observations from the SAMBA mooring array and similar analysis to define the precise characteristics of mesoscale eddies through depth. This will greatly improve the understanding of how these features influence the interocean exchange between the Indian and Atlantic Oceans. The circulation at the shelf edge, observed by the mooring located on the 1000m isobath, was shown to be driven by a combination of offshore mesoscale eddies, the position of the upwelling front and warm filaments formed at the reflection of the Agulhas Current. Identifying the influence of both the offshore mesoscale eddies and coastal upwelling at the shelf edge showed connectivity between the upwelling system and the offshore mesoscale variability. An example of the connectivity between the offshore mesoscale variability and the upwelling front was identified and presented. A dipole formed by two mesoscale eddies was observed to induced cross shelf transport advecting productive shelf waters offshore. The in situ observations were used to calculate the amount water transported from the shelf to the open ocean during this cross shelf transport event. The filament representing the cross shelf transport event was calculated to have a total volume of ~2 x 10¹² m³ with a volume transport of ~1Sv suggesting the event would have had a substantial impact on the local biology. The detailed analysis and quantification of the cross shelf transport event aimed to improve the current understanding of how mesoscale features interact with the upwelling system. In situ observations of cross shelf transport are rare, therefore the quantification of the amount of transported in the cross shelf transport event can serve as a baseline for future studies attempting to assess the impact of comparable cross shelf transport events on the local biology.
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    Investigating the relationship between volume transport and sea surface height in the Agulhas Current System
    (2018) Vermeulen, Estee; Hermes, Juliet C; Backeberg, Björn; Elipot, Shane; Vichi, Marcello
    The relationship between the volume transport of the Agulhas Current at 34°S (the position of the Agulhas Current Time-series array) and the gradient of sea surface height across the current was investigated using a regional Hybrid Coordinate Ocean Model. Previous studies have suggested a high correlation between SSH slope and Agulhas Current transport and, based on 3 years of in situ measurements, a transport proxy between along-track satellite data and in situ data was developed. The purpose of this modelling study was to re-create the Agulhas Current transport proxy in a virtual modelling environment, to test the validity of the underlying assumption on which the satellite-altimeter proxy was based. The Agulhas transport proxy assumed nine, constant linear relationships between SSH slope and integrated transport per unit distance over the 22-year transport time-series, based on the 3-year sampling period and a constant vertical stratification. The 34-year regional-hindcast from HYCOM provided the means to test the sensitivity of the transport proxy to vertical changes in the current and the length scale of observations used to build a constant, linear relationship between transport and SSH slope. During the investigation it was found that HYCOM contained exaggerated levels of offshore variability. This resulted in stronger correlations for the inshore linear regression models with a decreasing trend moving offshore. Based on the overall performance of the 34-year transport proxies it was concluded that the proxy was more capable of estimating the net transport of the Agulhas Current across the array instead of only the southwest transport component. Therefore, transport estimates inshore were more accurate than the transport estimates offshore, when the current is in a meandering state, and the poorer performance of the southwest transport proxy, specifically developed to capture the transport during offshore meander events, was less capable of estimating an accurate transport estimate. Results showed that calculating the proxy over longer time periods did not significantly improve the skill of the Agulhas transport proxy, suggesting the 3-years was a sufficient time-period used to develop the transport proxy in HYCOM. This study motivates the need to improve long-term monitoring methods, where the usage of numerical ocean models could help understand the sensitivities and limitations involved in the development of transport proxies in future.
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    Lateral carbon export from the southern Benguela upwelling system
    (2008) Swart, Neil C; Waldron, Howard
    The objective of this study was to quantify the lateral export of organic carbon from the continental shelf of the southern Benguela upwelling system to the open ocean. The flux is potentially important because the Benguela is one of the most productive and biogeochemically active ecosystems in the global ocean. Furthermore, a significant fraction of oceanic carbon storage is modulated through the biological pump mechanism, and on millennia 1 timescales the global ocean regulates atmospheric concentrations of carbon dioxide. The current study builds on previous work, and examines both the physical and biogeochemical aspects of the lateral carbon flux from the southern Benguela. Multiple physical mechanisms capable of inducing cross-shelf advection were examined, including dynamic interaction with Agulhas Rings and upwelling front instability, however the bottom boundary layer (BBL) was the focus.
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    Lateral carbon export from the southern Benguela upwelling system
    (2008) Swart, Neil C; Waldron, Howard
    The objective of this study was to quantify the lateral export of organic carbon from the continental shelf of the southern Benguela upwelling system to the open ocean. The flux is potentially important because the Benguela is one of the most productive and biogeochemically active ecosystems in the global ocean. Furthermore, a significant fraction of oceanic carbon storage is modulated through the biological pump mechanism, and on millennia 1 timescales the global ocean regulates atmospheric concentrations of carbon dioxide. The current study builds on previous work, and examines both the physical and biogeochemical aspects of the lateral carbon flux from the southern Benguela. Multiple physical mechanisms capable of inducing cross-shelf advection were examined, including dynamic interaction with Agulhas Rings and upwelling front instability, however the bottom boundary layer (BBL) was the focus.
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    On the subtropical front in the South Atlantic Ocean
    (2009) Funke, Michael
    The region surrounding the Tristan da Cunha Archipelago has received little attention to date due to its remote location. An extensive revision of previous literature covers the majority of oceanographic research undertaken in the region of interest. New satellite derived oceanographic data sets and the SODA Reanalysed model are used to overcome the sparse extent of in-situ data in this region. Using latitudinal temperature gradients to track the surface expression of the Subtropical Front from AMSR and OISST satellite derived sea surface temperature data reveals consistencies with previous literature.
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    Phytoplankton community structure determined through remote sensing and in situ optical measurements
    (2014) Evers-King, Hayley Louise; Bernard, Stewart; Henson, Stephanie; Shillington, Frank; Lucas, Mike
    Linking variability in optical signals with phytoplankton community characteristics is important to extend the use of the vast resource that is the satellite ocean colour archive. Detection of species, functional types or size classes has been addressed through a spectrum of empirical to analytical approaches. A key step in developing these techniques is quantifying the sensitivity in reflectance, which can be attributed to phytoplankton characteristics (e.g cell size) under different optical regimes. Ultimately, highly spatially and temporally resolved information on phytoplankton characteristics can help the global scientific community to answer important questions relating to primary ecosystem variability. In the southern Benguela, Harmful Algal Blooms threaten public health and the economic viability of fishery and aquaculture industries in the region. Concurrently, the dominance of phytoplankton biomass amongst optically significant constituents in the southern Benguela makes the region ideal for assessing the extent to which phytoplankton characteristics beyond biomass can influence the ocean colour signal. A forward and inverse approach is presented. Phytoplankton absorption and back scattering are generated from a phytoplankton particle population model coupled to two radiative transfer approaches: a reflectance approximation and the radiative transfer model, EcoLight-S. Non-linear optimisation inversion schemes are then implemented. A simulated dataset is created to investigate how much variability in reflectance can be associated with changes in phytoplankton cell size in different bio-optical water types. This dataset is inverted to investigate the errors inherent in the inversion process as a result of ambiguity. Comparison of the two radiative transfer techniques allows for consideration of the suitability of approximations for bidirection-ality and subsurface propagation. The inversion algorithm is then applied to hyperspectral in situ radiometric data to provide validation and further assessment of errors from all sources. Results indicate that size related sensitivity in reflectance is highly dependent on phytoplank-ton biomass, as determined by the relative phytoplankton contribution to the Inherent Optical Property budget. The algorithm is finally applied to ten years of MERIS data covering the southern Benguela. A time series of biomass and cell size is presented and metrics developed to demonstrate the utility of this approach for identifying previously unobserved interannual variability in Harmful Algal Blooms.
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    Primary productivity and its variability in the Atlantic Southern ocean
    (2014) Joubert, Warren Ryan; Monteiro, Pedro M S; Waldron, Howard
    The two principal bottom-up drivers of the High Nutrient Low Chlorophyll (HNLC) characteristics of the Southern Ocean are light and nutrient (mainly dissolved iron) limitation ( Boyd , 2002; Mitchell et al., 1991), which have varying limiting roles over the growing season ( Boyd, 2002; Swart et al., 2014). This research commenced with an investigation of the meridional characteristics of primary productivity in the Atlantic Southern Ocean during austral summer 2008.
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    Rainfall variability over southern Africa
    (2014) Driver, Penny Meredith; Reason, Chris; Abiodun, Babatunde Joseph
    Southern Africa is subject to high inter annual rainfall variability and the factors influencing southern African rainfall are not fully understood. The variability has been linked with various sea surface temperature anomalies (SSTAs) in each of the three major ocean basins as well as variability in the strength and position of regional atmospheric features. One of the atmospheric factors that may play a substantial role in southern African rainfall variability is the Botswana high, a high pressure cell which exists at the 500hPa level and is centred over central Namibia and western Botswana during austral summer. 20th Century reanalysis data is used to further investigate this feature and analysis reveals an association between the strength of the Botswana high and ENSO. Further analysis indicates that a connection between the Botswana high and rainfall over southern Africa not only exists during ENSO years, but is also apparent during neutral years that display ENSO-like characteristics in the Botswana high. This result may assist in producing better rainfall forecasts for non-ENSO years. The frequency of dry days over southern Africa during austral summer is investigated using GPCP observational data. Correlation analysis is generally in agreement with previous studies and showed that dry day frequency(DDF) over the Limpopo and North East Zambia regions is correlated with ENSO, while DDF over coastal northern Angola and central South Africa is correlated with SSTs in the Indian and Atlantic Oceans. The possible role played by DDF during JFM 1998 and JFM 2010 is investigated and results indicate that the distribution of DDF over southern Africa was notably different during these two seasons and may have contributed to the unexpected rainfall experienced over southern Africa.
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    Seasonal and interannual variability of surface chlorophyll-a and sea surface temperature in the Delgoa Bight, southern Mozambique
    (2015) Dove, Veronica Fernando; Shillington, Frank
    Multi satellite data for surface chlorophyll‐a (Chl‐a), sea surface temperature (SST), sea surface wind (SSW) and sea level anomalies (SLA) have been obtained and analysed over the Delagoa Bight (24‐28°S, 32‐36°E), southern Mozambique for the period 2003‐2012 at monthly time scales. Both descriptive and quantitative analysis using wavelets have been used to obtain a better understanding of the nature of the interannual, seasonal and intra- seasonal variability of the data. Strong seasonal structure and interannual modulation were observed in the area averaged Chl‐a concentration and SST. The lowest maximum in monthly Chl-a was in December (0.127 mg.m--‐3) and the highest in August (0.541 mg.m‐3). The lowest maximum in monthly SST was in August (21.8°C) and the maximum in February (27.9°C). The Chl‐a and SST were strongly anti-correlated and both exhibited a well- defined seasonal cycle, contrasting with the SSW and SLA. The daily observations of temperature at 17 meters depth, from the northern Delagoa Bight at Ponta Zavora (24.48°S- 35.24°E) for the period 2006‐2011, have confirmed a seasonal signal with amplitude of about 6.5°C. Cool coastal water events were found mostly in summer and spring, with maximum amplitude of 6°C. Further analysis of this daily data did not reveal the timing of such events to be regular.
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    The variability and dynamics of the Antartic Circumpolar Current south of Africa using proxy techniques
    (2009) Swart, Sebastiaan; Ansorge, Isabelle J; Speich, Sabrina; Lutjeharms, Johann R. E.
    The general circulation of the Southern Ocean is dominated by the eastward flowing Antarctic Circumpolar Current (ACC). This is a continuous feature linking the three major ocean basins and thus forms a vital link in the transport of heat and salt on a global scale. These exchanges provide a vital mechanism for the global thermohaline circulation (THC), which regulates the Earth's climate. In the high latitudes, where conditions are hostile, routine hydrographic observations are scarce resulting in a poor understanding of the physical and dynamic processes controlling the variability of the ACC and its influence on the THC. The GoodHope program launched in early 2004 aimed to establish an intensive monitoring platform that would provide detailed information on the physical structure and volume flux of water masses south of Africa. Sustained observations along the GoodHope cruise track provide the means to monitor the vertical structure and variability of the ACC and its associated fronts south of Africa. Such intense monitoring has been under way in the Drake Passage and south of Australia since the 1970s. A major objective of this thesis is to provide sound estimates of ACC transport and variability using both in situ measurements and remote sensing techniques. These estimates are crucial in understanding the role the ACC plays in the global thermohaline circulation (THC) and how the region south of Africa acts as a major conveyor of heat and salt to the higher latitudes. Baroclinic transports of the ACC, relative to 2500 dbar, are calculated from altimetry data alone. These transports agree with simultaneous observed estimates (rms difference in net transport is 5.2 Sv). These observations suggest that sea level anomalies largely reflect baroclinic transport variations above 2500 dbar. The transports contribution per ACC front shows that the SAF is responsible for the highest variability signals (>50%) even though its net transport contribution to the ACC was less (9%) than the APF. Furthermore, direct measurements of heat and salt content in the Southern Ocean are based on the few synoptic transects, the majority of which are restricted in the austral summer. To overcome the poor temporal and spatial resolution of measurements in the south African sector of the Southern Ocean, this thesis makes use of the gravest empirical mode (GEM) method and applies this technique to weekly composites of satellite altimetry data. The GEM method makes use of all available hydrographic casts from the south-east Atlantic Ocean and projects the data into a baroclinic stream function space parameterised by pressure and dynamic height. The GEM fields were shown to compare closely with independent in situ observations of the water column, capturing more than 97% of the total temperature and density variance in the ACC domain. The GEM-derived heat and salt content estimates attempt to determine the variability signals of the ACC due to external influences, such as topographical obstacles and oceanic features originating from subtropical regions. The exploitation of such proxy methods is useful in improving our understanding of the subsurface properties of the Southern Ocean and more importantly the influences temporal changes in the system have on the structure and transport of the ACC. With time, these methods will be refined with the input of new observations, thereby enhancing their ability to determine the dynamic nature of the ACC and its impact on the Earth's system.
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    The Weather of the Agulhas bank and the Cape South Coast
    (1987) Hunter, I T; Brundrit, Geoff
    Until 1982, when the National Research Institute for Oceanology (NRIO) erected self-contained, automatic weather stations (AWS) on the Cape South Coast, no continuous coastal measurements were available. This Institute had erected an AWS on the drilling rig Sedco K in 1978, so that over 3 years of very valuable off- shore data was already available on the adjacent Agulhas Bank. Al though the weather offices at George and Port Elizabeth have made accurate meteorological observations for over 30 years, this data is shown here to differ significantly from actual coastal measurements. Thus the NRIO AWS network, which operated for just over a year, provided a detailed, short-term data set for the study of coastal weather processes. In order to acquire longer term data from coastal observations, five years of hourly wind observations from lighthouse keepers along the Cape South Coast were also utilised. Although these are estimates, it is shown that a coastal estimate may be more representative of marine conditions than an anemometer reading some distance inland. Voluntary Observing Ship's data (VOS) extracted from SADCO's Marine Climatology database, provided the long-term offshore information, whilst also supplying very useful 'present weather' (synoptic code ww) observations for case studies. Observations from synoptic stations for the period that the coastal AWS were deployed (February 1982 - March 1983), were provided by the South African Weather Bureau. With this unique and comprehensive data set, the various weather systems affecting the region are discussed. Twelve case studies form the main reference for this discussion, which includes relevant oceanographic parameters. The weather systems are considered firstly as individually propagating circulations with the AWS network providing details of propagation speeds and coastwise development. Secondly the combined 'weather producing' effects of these systems are discussed, with a strong emphasis being placed on man/weather interactions. It is shown that certain operations along the Cape South Coast and over the Agulhas Bank, are extremely weather sensitive, and would benefit considerably from an increased knowledge of weather processes. Recommendations aimed not only at those managing weather sensitive operations, but also at those involved in coastal meteorological measurement and research, complete the thesis.