Wind Stress and Surface Waves Observed on Lake Washington

Abstract

New results from turbulent flux measurements made over Lake Washington include the following: 1) The only direct measure of the vertical transport of the horizontal momentum, heat, and matter in the surface boundary layer is the so-called eddy correlation method. However, even if the measurement errors are negligible, the results obtained from point observations may show large scatter due to lack of stationarity and horizontal homogeneity in the turbulent field and to the sampling variability. Scatter may be greatly reduced by spatial averaging. In this study, such an effect is achieved by determining the surface roughness length, hence the neutral drag coefficient, from the measured wave height spectrum, which reflects the atmospheric input integrated over the fetch. Applicability and usefulness of the approach for general field measurements and remote sensing is discussed. 2) The evolution of the wave field observed on Lake Washington agrees in peak frequency and the slope of the equilibrium range parameter α as a function of ?wind forcing? with other observations, while the magnitude of α is significantly smaller (by a factor of 2.1) than the values obtained from larger bodies of water. Based on the results obtained from a wave model, we attribute this observed difference to the narrower width of the water body on Lake Washington. These findings indicate that the state-of-the-art spectral parameterization of surface waves has limitations in describing the observations from a natural but small body of water.