Search Results
You are looking at 1 - 10 of 56 items for
- Author or Editor: Jin Wu x
- Refine by Access: All Content x
Abstract
No abstract available.
Abstract
No abstract available.
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.
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.
Abstract
A greater volume of air is entrained by breaking waves to produce many more bubbles in salt, than in fresh, water. There are, however, little differences in their sizes. These results are consistent with reported observations of whitecaps over freshwater lakes and the ocean.
Abstract
A greater volume of air is entrained by breaking waves to produce many more bubbles in salt, than in fresh, water. There are, however, little differences in their sizes. These results are consistent with reported observations of whitecaps over freshwater lakes and the ocean.
Abstract
Wind-induced shell currents and wave-induced mass transports at various fetches of both clean and slick sea surfaces are separately estimated. At the clean surface, the ratio between wind-induced current and wind velocity decreases, while the ratio between wave-induced current and wind velocity increases, with increasing fetch. The total surface drift current, the sum of wind- and wave-induced components, decreases gradually with increasing fetch and approaches 3.1% of wind velocity at long fetches, comparing very favorably with measured values. At a slick surface, the wind-induced drift current is reduced due to a decrease of the wind-stress coefficient, and the wave-induced mass transport is increased due to an additional wave damping. As a result of these opposite effects, the total surface drift current at a slick surface differs much less significantly than individual components from that at a clean surface. It is also suggested that the surface mass transport can be calculated simply from characteristics of dominant waves and that discrepancy between earlier measured currents of clean and slick surfaces is due to a direct momentum flux from wind to waves. Finally, linear superposition of wind- and wave-induced components and effects of water depth on surface drift currants are discussed.
Abstract
Wind-induced shell currents and wave-induced mass transports at various fetches of both clean and slick sea surfaces are separately estimated. At the clean surface, the ratio between wind-induced current and wind velocity decreases, while the ratio between wave-induced current and wind velocity increases, with increasing fetch. The total surface drift current, the sum of wind- and wave-induced components, decreases gradually with increasing fetch and approaches 3.1% of wind velocity at long fetches, comparing very favorably with measured values. At a slick surface, the wind-induced drift current is reduced due to a decrease of the wind-stress coefficient, and the wave-induced mass transport is increased due to an additional wave damping. As a result of these opposite effects, the total surface drift current at a slick surface differs much less significantly than individual components from that at a clean surface. It is also suggested that the surface mass transport can be calculated simply from characteristics of dominant waves and that discrepancy between earlier measured currents of clean and slick surfaces is due to a direct momentum flux from wind to waves. Finally, linear superposition of wind- and wave-induced components and effects of water depth on surface drift currants are discussed.
Abstract
Microwave specular reflections from the sea surface under low and intermediate winds are mainly from ocean ripples. Altimeter returns reported recently from stormy seas appear to be reflections from roughnesses produced by breaking waves, clearing the way for measuring hurricane winds from space. A continuous function is also proposed to determine, from altimeter returns, sea surface wind speeds from breeze to hurricane.
Abstract
Microwave specular reflections from the sea surface under low and intermediate winds are mainly from ocean ripples. Altimeter returns reported recently from stormy seas appear to be reflections from roughnesses produced by breaking waves, clearing the way for measuring hurricane winds from space. A continuous function is also proposed to determine, from altimeter returns, sea surface wind speeds from breeze to hurricane.
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.
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.
Abstract
Experimental results of Blanchard and Syzdek and of Resch and Afeti on the production of film drops by bubbles bursting at the surface of seawater were parameterized earlier by Wu. More recently, comprehensive observations have been carried out by Spiel. All these measurements, covering different size ranges of film drops, are shown to quantitatively complement each other. Through combining these results, the production of film drops has been quantified, in terms of both number and size distribution, over the entire radius range 0.01–250 μm. The average size of film drops is about 25 μm in radius, which is much larger than the commonly cited radius for film drops of 5 μm. In addition, all the results are shown to follow a simple rule; that is, the ratio between the total surface area of film drops and the surface area of their parent bubble is a constant.
Abstract
Experimental results of Blanchard and Syzdek and of Resch and Afeti on the production of film drops by bubbles bursting at the surface of seawater were parameterized earlier by Wu. More recently, comprehensive observations have been carried out by Spiel. All these measurements, covering different size ranges of film drops, are shown to quantitatively complement each other. Through combining these results, the production of film drops has been quantified, in terms of both number and size distribution, over the entire radius range 0.01–250 μm. The average size of film drops is about 25 μm in radius, which is much larger than the commonly cited radius for film drops of 5 μm. In addition, all the results are shown to follow a simple rule; that is, the ratio between the total surface area of film drops and the surface area of their parent bubble is a constant.
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.
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.
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.
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.
