Characteristics of ocean gravity waves off the Cape South West coast

 

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dc.contributor.advisor Harris, T F W en_ZA
dc.contributor.advisor Hennessy, Thomas Richard en_ZA
dc.contributor.author Shillington, Frank Alan en_ZA
dc.date.accessioned 2016-03-15T07:17:11Z
dc.date.available 2016-03-15T07:17:11Z
dc.date.issued 1974 en_ZA
dc.identifier.citation Shillington, F. 1974. Characteristics of ocean gravity waves off the Cape South West coast. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/17789
dc.description.abstract Ocean gravity waves have been recorded near Melkbosstrand with a Wemelsfelder float type wave recorder on a sea tower situated in water 13m deep and one Kilometre offshore. The half hour records, taken twice daily between July 1972 - June 1973, have been analysed in a format uniform with that of Draper (1966). Measurements have been made from the wave records to check the value of the statistical ratios of Longuet- Higgins (1952) and Draper (1963). Ratios of maximum wave height to root mean square amplitude are lower than the theoretical values and reasons for this are discussed in the light of the records being taken in shallow water. Ratios of maximum wave height to the average upper one tenth wave height and average upper one third wave height agree closely with the theoretical values. Spectral analysis using the methods of Blackman and Tukey (1958), with 36 degrees of freedom and 100 lags have been applied to half hour records digitized once per second. Frequency, time diagrams contoured at equal energy values have been constructed for the period May and part of June 1973 on the basis of twice daily spectral measurements at 5 mHz intervals. The wave events, which include generation of swell from near South Georgia, (54°S, 37°W), have been compared with the South African Weather Bureau synoptic charts in order to identify generation centres. Repeated energy values near the 50 mHz band seem to be generated by winds of a lower velocity than required by Moskowitz (1964). Predominant siting of fetches at distances of the order of 1000 nautical miles accounts for the bulk of wave generation between latitudes 40° - 50°S. One storm appears to have originated near the Drake passage, but no events have been detected with waves passing through the passage. Analysis of wave spectra from several storms generating maximum wave heights over 5 metres, show that fully developed seas are seldom, if ever, present in Cape waters. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Oceanography en_ZA
dc.title Characteristics of ocean gravity waves off the Cape South West coast en_ZA
dc.type Master Thesis
uct.type.publication Research en_ZA
uct.type.resource Thesis en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Department of Oceanography en_ZA
dc.type.qualificationlevel Masters
dc.type.qualificationname MSc en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Shillington, F. A. (1974). <i>Characteristics of ocean gravity waves off the Cape South West coast</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/17789 en_ZA
dc.identifier.chicagocitation Shillington, Frank Alan. <i>"Characteristics of ocean gravity waves off the Cape South West coast."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 1974. http://hdl.handle.net/11427/17789 en_ZA
dc.identifier.vancouvercitation Shillington FA. Characteristics of ocean gravity waves off the Cape South West coast. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 1974 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/17789 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Shillington, Frank Alan AB - Ocean gravity waves have been recorded near Melkbosstrand with a Wemelsfelder float type wave recorder on a sea tower situated in water 13m deep and one Kilometre offshore. The half hour records, taken twice daily between July 1972 - June 1973, have been analysed in a format uniform with that of Draper (1966). Measurements have been made from the wave records to check the value of the statistical ratios of Longuet- Higgins (1952) and Draper (1963). Ratios of maximum wave height to root mean square amplitude are lower than the theoretical values and reasons for this are discussed in the light of the records being taken in shallow water. Ratios of maximum wave height to the average upper one tenth wave height and average upper one third wave height agree closely with the theoretical values. Spectral analysis using the methods of Blackman and Tukey (1958), with 36 degrees of freedom and 100 lags have been applied to half hour records digitized once per second. Frequency, time diagrams contoured at equal energy values have been constructed for the period May and part of June 1973 on the basis of twice daily spectral measurements at 5 mHz intervals. The wave events, which include generation of swell from near South Georgia, (54°S, 37°W), have been compared with the South African Weather Bureau synoptic charts in order to identify generation centres. Repeated energy values near the 50 mHz band seem to be generated by winds of a lower velocity than required by Moskowitz (1964). Predominant siting of fetches at distances of the order of 1000 nautical miles accounts for the bulk of wave generation between latitudes 40° - 50°S. One storm appears to have originated near the Drake passage, but no events have been detected with waves passing through the passage. Analysis of wave spectra from several storms generating maximum wave heights over 5 metres, show that fully developed seas are seldom, if ever, present in Cape waters. DA - 1974 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1974 T1 - Characteristics of ocean gravity waves off the Cape South West coast TI - Characteristics of ocean gravity waves off the Cape South West coast UR - http://hdl.handle.net/11427/17789 ER - en_ZA


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