Observed physical and environmental causes of scatter in whitecap coverage values in a fetch-limited coastal zone

Abstract

Meteorological and oceanographic data along with sea surface images were recorded at a fetch-limited coastal site to investigate the effect of physical and environmental conditions on whitecap coverage W. An automated image-processing technique allowed over 100,000 images to be analyzed for W. Data analysis showed that many processes influenced W. The presence of tidal currents appeared to have augmented values of W under certain specific conditions. Analysis of wave spectra indicated the ubiquitous presence of swell propagating northward. Scatter in W was markedly absent in mixed seas when the spectral intensity of the wind waves was of the same order of magnitude as the spectral intensity of the swell waves. Swell-dominated seas introduced much more scatter in W. W was approximately one third lower in swell-dominated seas than in mixed seas. Specifically, steep swell waves (steepness values greater than 0.01) that propagated opposite to wind wave direction appeared to have reduced W at wind speeds below approximately 7.5 m s(-1), but this effect needs more investigation. The coastal site enabled the possibility of investigating physical and environmental effects on W that would otherwise have been more difficult to observe in the open ocean.