Array measurements of atmospheric pressure fluctuations above surface gravity waves

Abstract

A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays ask−νwherekis the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

Source term balance in a severe storm in the Southern North Sea

“…Wind input is based on the parameterisation by Snyder et al (1981). The focus of this paper is to assess the effect of applying different whitecapping formulations.…”

“…The WAM model (WAMDI 1988) contains also source terms for wind input according to the Snyder et al (1981) parameterisation and whitecapping dissipation according to Komen et al (1984Komen et al ( , 1994. For shallow water applications, a bottom friction term according to the JONSWAP (Hasselmann et al 1973) was added.…”

Sea surface wind stress and drag coefficients: The hexos results

“…Measurements of correlation of air pressure and wave slope (e.g., Snyder et al, 1981) show that wind momentum is absorbed by young, growing waves. Nordeng (1991) estimates the influence on the drag coefficient of wave growth and of taking the wind velocity relative to the wave velocity, integrated over the wave spectrum.…”

Wave modelling – The state of the art

“…Observations in the field from Snyder et al (1981) and Hasselmann and Bosenberg (1991) do not support the idea that there is a substantial wave damping for waves propagating faster than the wind. In the lab, however, Donelan (1990) which parameterizes growth and damping in terms of the wind speed at height λ/2.…”

“…It ignores, however, a possible change of wind profile while the ocean waves are evolving. The momentum transfer from wind to waves may be so large that the associated wave-induced stress becomes a substantial fraction of the turbulent stress (Snyder, 1974, Snyder et al, 1981. The velocity profile over sea waves is controlled by both turbulent and wave-induced momentum flux.…”