||Coastal zone is the interface among the ocean, atmosphere and the land, where, the flux of terrestrial (i.e. sediment, nutrients and pollutants etc.), heat and momentum transfer take. The transportation and dispersion of terrestrial material in coastal waters and estuaries are mainly controlled by tidal current, wind-driven current and density flow, among them, the wind-driven current that incurred by the wind stress is the dominate mechanism. As the characteristics of wind variation will bring direct impacts to the ocean surface, understanding the oscillation of surface wind fields on the coastal waters are essential to the realization of nature environments as well as the application such as the coastal engineering and marine energy utilization).|
From the viewpoint of practical application, renewable energy conversion had become an increasing source in recent years. Due to the restriction of limited land area of, Taiwan island, the utilization of off-shore wind energy had gained the importance. Temporal oscillation of wind speed in various scale will affect the Capacity Factor(CF), for which, small CF will result in high cost/benefit ratio. The aim of this study is to use existing observation wind data, explore the characteristics of the temporal oscillation of coastal wind fields around Taiwan waters, with the hope to assist the off-shore wind power generation.
Previous studies had shown that the surface wind exhibit significant diurnal and semidiurnal periodicity, due to several mechanisms such as atmospheric tide and land-sea breeze. Hence, the aim of this article is twofold. First, in order to fulfill the needs from off-shore wind farms application around Taiwan, the statistical descriptions of the coastal wind speed oscillation and associated characteristics of seasonal and spatial variations are discussed. Second, the causes and mechanisms of the diurnal and semidiurnal periodicity wind around Taiwan waters are investigated using short-time rotary spectral analysis.
The results show that surface wind features diurnal oscillation around Taiwan waters. There was a significant seasonal difference of the intensity of diurnal and semidiurnal wind. The categorization of the coastal zone with respect to surface wind can be divided into several regions, i.e. the northwestern coast, southwest coast and east coast. Consider the wind ellipses features, the diurnal oscillation amplitude is 2-3 times higher than semidiurnal cycle, the low-latitude coastal has higher oscillation intensity, followed for the east coast, west coast is smallest. The statistics of the direction of major axis of the diurnal wind ellipses, Hsichu and Yung-an feature similar characteristic, Dapeng Bay and Xiao Liuqiu also have same characteristic, the other station showed descrepencies, which might owing to the differences in terrain and surface friction. As a whole, land-sea breeze is the dominating factor to the diurnal wind and the effects from atmosphere tide cannot be ignored.
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