A tower‐mounted optical device is used to measure the two orthogonal components of the sea surface slope. The results indicate that an unstable stratification at the air‐sea interface tends to enhance the surface roughness. The presence of a long ocean swell system steers the primary direction of shortwave propagation away from wind direction, and may increase or reduce the mean square slope of the sea surface.

Measurements of the aerodynamic pressure distribution at the interface between air and simple progressive water waves are obtained with the use of a pressure sensor that follows the water surface. The theory of Miles (1957, 1959) and Benjamin (1959) on shear flows past a wavy boundary predicts a phase shift between the pressure distribution along the boundary and the boundary itself. An experimental verification of this theory is sought especially. A wind–wave facility 115 ft. long, 6 ft. high and 3 ft. wide was used. The facility is equipped with an oscil-lating-plate wave-generator which is capable of generating sinusoidal or arbitrary wave-forms, and a suction fan which can produce wind velocities up to 80 ft./sec when the water is at a nominal depth of 3 ft. The pressure sensor used for the measurements of pressure, was mounted on an oscillating device such that the sensor could be maintained at a fixed small distance (within 1/4 in.) above a propagating wavy surface at all times. The perturbation pressure over progressive waves is extracted from recorded data sensed by the moving sensor. The results compare favourably with the theoretical predictions of Miles (1959).

A hot‐film anemometer was used in a wind flume to measure the size and number of water droplets over the air‐water interface. Experiments were conducted both with and without mechanically generated waves and each with both freshwater and saltwater. The effects of wind speed and wave height on the vertical distribution of spray were investigated. The mechanism of spray generation was explored. The results of this study indicate that the vertical distribution of the total horizontal flux of droplets can be expressed by a logarithmic distribution. The drop size distribution (drop size spectrum) at a fixed elevation can be described by a negative power law of drop diameter. The droplet production mechanism by bursting bubbles suggested by Blanchard (1963) is found to account for only a portion of the total production. The effect of spray on the remote sensing of the air‐sea interface is evaluated. The spray is found to affect strongly the measurements obtained from a radiometer.

No abstract

Hydrodynamic modulation of wind waves by long surface waves in a wave tank is investigated, at wind speeds ranging from 1.5 to 10 m s−1. The results are compared with the linear, non-dissipative, theory of Longuet-Higgins & Stewart (1960), which describes the modulation of a group of short gravity waves due to straining of the surface by currents produced by the orbital motions of the long wave, and work done against the radiation stresses of the short waves. In most cases the theory is in good agreement with the experimental results when the short waves are not too steep, and the rate of growth due to the wind is relatively small. At the higher wind speeds, the effects of wind-wave growth, dissipation and wave-wave interactions are dominant.