2 research outputs found
Revised Estimates of Ocean Surface Drag in Strong Winds
Air-sea drag governs the momentum transfer between the atmosphere and the
ocean, and remains largely unknown in hurricane winds. We revisit the momentum
budget and eddy-covariance methods to estimate the surface drag coefficient in
the laboratory. Our drag estimates agree with field measurements in
low-to-moderate winds, and previous laboratory measurements in hurricane-force
winds. The drag coefficient saturates at and , in agreement with previous laboratory results by
Takagaki et al. (2012). During our analysis, we discovered an error in the
original source code used by Donelan et al. (2004). We present the corrected
data and describe the correction procedure. Although the correction to the data
does not change the key finding of drag saturation in strong winds, its
magnitude and wind speed threshold are significantly changed. Our findings
emphasize the need for an updated and unified drag parameterization based on
field and laboratory data.Comment: 13 pages, 5 figure
Gravity-Capillary Wave Spectral Modulation by Gravity Waves
In order to more fully understand the specific hydrodynamic relationship between young wind-generated gravity-capillary waves and longer gravity waves, a laboratory experiment was devised to observe changes in short wave spectral behavior over the phase of a long wave. This paper endeavors to expand on the body of laboratory wave modulation data and extend the investigation in support of the radar remote sensing of ocean surface waves. Measurements were made in the University of Miami's surge-structure-atmosphere interaction facility in the air-sea interaction saltwater tank wind-wave tank, with 10 m referenced wind speeds ranging between 5 and 23 m/s and paddle-generated wave steepnesses "ak" varying between 0.05 <; ak <; 0.3. A polarimetric camera was used to capture high sampling frequency maps of wave slope, yielding spatiotemporal information about short wind-wave behavior [provided as temporal variations in the wavenumber spectrum, where k ≈ 15(100-1000) rad/m]. The simultaneous and colocated long wave phase was measured via a side-looking camera. Hydrodynamic modulation transfer function (MTF) phases are found to be in general agreement with established values (between 2 and 10 radians) at the given wind speeds. The positive phase of the modulation places it immediately downwind of the long wave crest, with MTF magnitudes strongest for high wavenumbers at the lowest wind speeds. The results are also presented to show the modulation of gravity-capillary and pure capillary waves as variations in mean square slope over the long wave phase, with peak roughness enhancement found to move upwind of the long wave crest with increasing wind forcing