Abstract
Fetch-limited wave growth was analyzed using high spatial and temporal resolution measurements obtained with high-frequency (HF) radars. To calculate the wave spectrum, the second-order echo (S2N) was extracted from the Doppler spectrum and mapped to the wave frequency domain. The conversion of S2N to the wave frequency spectrum was carried out using a linear parametric model dependent on wind speed. Wave growth, represented by the dimensionless energy and peak frequency as a function of dimensionless fetch, was determined from the spectra calculated for 25 cells (~400 km2) in the vicinity of a moored Air–Sea Interaction Spar buoy. The buoy data were used as reference and to provide the wind information required for the wave growth analysis. The simultaneous data from the buoy and HF radars showed a suitable agreement with the wave growth curves. The analysis of the 25 cells showed an adequate agreement and certain dispersion around the growth curves. Possible causes of this dispersion are related to errors in the estimation of the frequency spectrum and fetch, and the assumption of homogeneous wind conditions. From the limited data set used, it was not possible to prove any impact of swell on wave growth; however, it is possible that analysis over a wider range of swell heights may provide this evidence. Nevertheless, the results suggest that the linear parametric model is able to reproduce fetch-limited wave growth. This work represents the first effort focused on fetch-limited wave growth using HF radars.
Highlights
Understanding the processes governing the generation, growth, and evolution of ocean waves is necessary to predict their effects on coastal and ocean dynamics
Ocean wave data were measured by a capacitance wire array (García-Nava et al 2009) and used to calculate the wave spectrum; the directional wave spectrum was calculated only for the first 10 days, but the wave frequency spectrum data are available for the entire study period
During the Tehuano wind events, una altura de 10 m (U10) values were as high as 20 m s–1, whereas remained approximately constant (180o)
Summary
Understanding the processes governing the generation, growth, and evolution of ocean waves is necessary to predict their effects on coastal and ocean dynamics. Waves are generated and grow as a result of the force exerted by the wind on the sea surface. Storm-associated winds in the open ocean generate waves that can travel thousands of kilometers. Storms occur randomly in space and time; measuring wave growth is difficult because there is no prior knowledge of where and when they will originate and sufficient wave-measuring instruments are not in place. Waves that are generated and begin to grow in an area affected by strong winds are typically referred to as wind sea. Wave growth can be influenced by physical mechanisms such as atmospheric stability, swell, wind variability (Hwang et al 2011), wave–current interactions (Kahma and Calkoen 1992), and the distance over which wave growth occurs, called the fetch (Ardhuin et al 2007)
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