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Jin Wu

Abstract

Friction velocities of pulsating winds were measured, as well as slope and curvature distributions of thedisturbed water surface. The results obtained with the same average wind speed, but with pulsations of various frequencies and amplitudes are compared. The pulsations are found to be critical on wind and wavestructures when the regime of the wind boundary layer is affected. The influence of pulsations becomes secondary, when the wind boundary layer is aerodynamically rough. A distinct feature of this regime, generallyoccurring in the field, is that more capillaries are produced by pulsating winds.

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Jin Wu

Abstract

Two approaches have been adopted to construct altimeter wind algorithms: one is based on the mean-square sea surface slope, and the other is based on the Seasat scatterometer wind. Both types of algorithms are critically reviewed with respect to the mechanism governing near-nadir radar sea returns and the comparison between altimeter and buoy winds. A new algorithm is proposed; it is deduced on the basis of microwave specular reflection and is finely tuned with buoy-measured winds. On the basis of this algorithm and the formula of the wind-stress coefficient, a simple wind-stress algorithm is also proposed.

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Jin Wu

Abstract

The increase of the wind-stress coefficient with wind velocity was found to start with winds as light as 3 m s−1, below which, following the formula for aerodynamically smooth flows, the wind-stress coefficient decreases as the wind velocity increases. This therefore imposes a lower wind-velocity bound on some previously proposed formulae and modifies the interpretation of some others.

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Jin Wu

Abstract

An altimeter wind algorithm that was proposed earlier and deduced on the basis of microwave specular reflections from the sea surface is discussed. This algorithm is further tuned overall with buoy-measured winds; it is refined at low winds (<2.4 m s−1) in accordance with the surface-layer characteristics and scatterometer winds, and validated at high winds (>9.6 m s−1) with tower and airborne observations. Recent efforts comparing various altimeter wind algorithms are aim discussed.

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Jin Wu

Abstract

At low and intermediate winds, altimeter returns are from ocean waves having their length longer than the radar wavelength. These waves, mainly ripples, are generated and modified by wind stress and dominant ocean waves. The wind stress coefficient is greater with steeper dominant waves prevailing at shorter fetches, and the attenuation of ripples is also stronger with steeper dominant waves. The combined influence of dominant waves on the altimeter wind algorithm is shown to be small as a result of these compensatory effects at short fetches, with an intensified generation by the augmented wind stress and an escalated suppression by steeper dominant waves.

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Jin Wu

Abstract

Stability parameters and wind-stress coefficients under various atmospheric conditions are related to wind velocity and air-sea temperature difference. Readily applicable formulae, without iterative computations, of wind-stress coefficients under these conditions are presented.

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Jin Wu

Wind, driving oceans, and the links between them to the atmosphere compose a critical parameter for the world circulation model as well as for the evaluation of climate changes. Traditionally, wind velocities have been reported by ships of opportunity and recorded on a network of buoys; they have also recently been generated by numerical weather prediction models and mapped with spaceborne remote sensors. Wind speeds from buoy measurements, shipobservations, and model computations are compared, using the globally available altimeter returns that they have in common. Large, systematic deviations are found among the results obtained with these techniques, cautioning against extensive use of these wind speeds.

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Jin Wu

Abstract

No abstract available.

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Jin Wu

Abstract

The distributions of water-surface slopes and wave heights were measured under suddenly started and stopped winds. The root-mean-square slopes and average wave heights are found to grow and decay exponentially with time; in each case, the growth rate is faster than the decay rate. Quantitative growth and decay rates of these slopes and heights approaching and departing an equilibrium state, respectively, are presented. The growth rates show strong dependence and the decay rates show insignificant dependence an wind-friction velocity. The growth time of slope statistics is found to be shorter than that of height statistics, suggesting that the ripples can be excited directly and effectively by the wind and that wave-wave interaction and wind gusts are important to wave generation by wind. This comparison, along with measurements of instantaneous growth of microscopic surface structures reported by others, also reveals that the development of the wave spectrum indeed starts at the high-frequency end, and that for remote sensing of sea-surface wind an uncertainty is introduced by unsteadiness of the wind.

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Jin Wu

Abstract

The slopes of ripples and the profiles of their carrier waves were simultaneously measured in a wind-wave tank with winds of various velocities blowing over preexisting, long, regular surface waves. The results include the apportionment and the slope distributions (and therefore the mean-square slopes) of ripples located on various portions of the carrier-wave profile. At low wind velocities, the surface-tension governing regime of wind-wave interaction, the leeward face of the carrier wave was found to contain more ripples than the windward face. The parasitic capillaries are concentrated on the upper half of the leeward face, and move along the leeward face toward the trough of carrier waves as the wind velocity increases. At high wind velocities, the gravity governing regime of wind-wave interaction, the ripples become more evenly distributed on the leeward and on the windward faces. How ever, the ripples on the windward face are concentrated near the carrier-wave crest, and the ripples on the leeward face are concentrated near the carrier-wave trough. At all wind velocities, the rms slope of ripples on the windward face of the carrier waves is greater than that on the leeward face.

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