Abstract
Numerous studies have identified the complexities of the wave climatology around the South African coast, but limited studies have investigated these complex dynamics in the available literature. Several freely available parameterized wave boundary conditions are produced around southern Africa. However, none of these are fully spectral outputs from global or larger regional spectral wave models. This constraint results in local engineering and scientific organizations, reconstructing their own spectral boundary conditions. For coastal models, this is a reasonable assumption, assuming that the single parameterization is accurate and a representation of a non-multimodal sea state. The South African Weather Service (SAWS) Marine unit recently launched their coupled, operational wave and storm surge forecasting model. The aim of the SAWS Wave and Storm Surge (SWaSS) platform was to provide accurate, high-resolution coastal forecasts for the entire South African coastline. The present investigation thus presents the validation of the spectral wave component of the coupled system, developed in Delft3D. Various wave boundary reconstructions are investigated together with the two most used and well-known whitecapping formulations. Validation is performed with both in situ wave-rider buoy data (at nine locations along the coastline) and regional remotely sensed, along track, altimetry data. Full model performance statistics are provided, and the accuracy of the model is discussed.
Highlights
Southern Africa has been known for its extreme wave climate for centuries
Their nadir-looking instruments, which measure along a narrow beam directly below the satellite, measure scattered energy, which is the basis for the derived wave height and wind speed
The global WW3 model validation results is known as Ocean Quality Control (OCNQC) and these results are made available on the Global Ocean Data Assimilation Experiment (USGODAE) server [31]
Summary
Southern Africa has been known for its extreme wave climate for centuries. In the 1600s, the Cape Peninsula was dubbed the “Cape of Good Hope”, and the “Cape of Storms”, due to the large number of merchant ships that sank in extreme storm conditions [1]. Global distributions of wind sea and swell probabilities, indices and significant wave heights (based on collocated TOPEX/NSCAT and TOPEX/QSCAT datasets) confirm the heterogeneous behaviour of the southern African wave fields [11]. The sensitivities of regional- and local-scale (down to approximately 300 to 500 m resolution) spectral wave models have not yet been investigated for southern Africa. The aforementioned models do, provide boundary conditions to regional models and are archived in numerous, storage space-efficient, ways These storage techniques can vary in reliability in terms of representing the correct wave energy distribution at a particular point (e.g., the amount of energy associated with wind or swell seas). The prediction sensitivity of a regional SWAN spectral wave model for southern Africa is investigated.
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