Sea surface temperatures around the souhtern [i.e. southern] African coast : climatological aspects and applications

Greenwood, Karin C. (2003-04)

Thesis (MSc)--Stellenbosch University, 2003.

Thesis

ENGLISH ABSTRACT: The oceanic and meteorological systems that characterize the southern African coastline are well-documented. In this thesis, these characteristics have been considered in conjunction with the analysis of a unique set of sea surface temperature (SST) data, obtained from measuring sites around the southern African coast, to determine the variability of SSTs in the immediate coastal region of southern Africa, and to demonstrate how this variability impacts on marinerelated economic activities. As part of the analysis process, various statistical techniques have been applied to the data over different time periods to establish the extent of the spatial variability of SSTs along the southern African coastline. From the results it has been possible to identify three distinctly different 'climatological' regions around the southern African coast; viz a cooler west coast region with a low annual and seasonal SST variability and a higher variability from day-ta-day, a warmer east coast region with a higher annual and seasonal SST variability and a lower variability from day-ta-day; and a temperate south coast region with a highly erratic annual, seasonal and day-ta-day SST variability. Furthermore, it has been possible to identify, albeit small, the existence of a high and a low frequency signal of 12-15 days and 40-60 days, respectively, in the three different regions. There is also evidence of the periodic occurrence of anomalously warm and cold SST events in all three regions, and a probability of <1.1% of a day-ta-day SST anomaly of >3°C (+3°C or- 3°C) occurring anywhere along the southern African coastline. The general causes of SST change have been discussed within the context of the heat budget equation. Furthermore, the effects of the variability of SST on the climate and marine life around southern Africa and the resulting impact on the various marine-related economic activities (such as aquaculture, air-sea rescue and power stations) have been identified, and shown to be both positive and negative.Finally, it should be noted, that economic infonnation relating to marine activities is closely guarded due to inter-industry competition. It has therefore been difficult to quantify the exact impact of the effects of SST variability on these activities.

AFRIKAANSE OPSOMMING: Die oseaniese en weerkundige stelsels wat die kuslyn van suidelike Afrika kenmerk is goed gedokumenteer. Die stelselkenmerke is in hierdie verhandeling ondersoek aan die hand van 'n unieke datastel van seeoppervlaktemperature (SST) afkomstig van meetplekke aan die kus van suidelike Afrika, ten einde die veranderlikheid van SST in die onmiddelike kusomgewing van suidelike Afrika vas te stel, asook om te demonstreer hoe hierdie veranderlikheid inwerk op seeverwante ekonomiese aktiwiteite. As deel van die proses van analise is verskeie statistiese metodes gebruik om die data oor verskeie tydperke te ontleed ten einde die omvang van ruimtelike veranderlikheid van SSTs langs die kus van suidelike Afrika te bepaal. Uit die resultate was dit moontlik om drie duidelike onderskeibare 'klimatologiese' streke aan die kus van suidelike Afrika te identifiseer; te wete 'n koeler weskusstreek met 'n lae jaarlikse en seisoenale SST-veranderlikheid en hoër dag-tot-dag veranderlikheid, 'n warmer ooskusstreek met 'n hoër jaarlikse en seisoenale SST-veranderlikheid en laer dag-tot-dag verandelikheid; asook 'n gematigde suidkusstreek met 'n hoogs wisselvallige jaarlikse, seisoenale en dag-totdag SST-veranderlikheid. Dit was verder moontlik om, alhoewel klein, die bestaan van lae en hoë frekwensie seine van 12-15 dae en 40-60 dae onderskeidelik in die drie streke te identifiseer. Daar is ook tekens van die periodieke voorkoms van anomale warm en koue SSTgebeurtenisse in al drie streke en 'n waarskynlikheid van <1.1% van die voorkoms van 'n dagtot- dag SST-anomaliteit van >3°C (+3°C of -3°G) op enige plek langs die suider Afrikaanse kuslyn. Die algemene oorsake van veranderings in SST is bespreek binne die konteks van die formule vir die behoud van hitte-energie. Die invloed van SST-veranderlikheid op die klimaat en die seelewe om suidelike Afrika en die gevolglike effek op mariene-verwante ekonomiese aktiwiteite (soos akwakultuur, lug-see-redding en kragstasies) is ook geïdentifiseer en is aangetoon om beide positief en negatief te wees Ten laaste dien dit gemeld te word dat ekonomiese inligting met betrekking tot mariene aktiwitweite goed bewaar word as gevolg van kompetisie in die bedryf. Dit was derhalwe moeilik om die presiese impak van die gevolge van SST-veranderlikheid op sodanige aktiwiteite te kwantifiseer.

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