Measurement of skin friction distribution along the surface of wind waves     

Kuniaki Okuda  Sanshiro Kawai  Yoshiaki Toba 《Journal of Oceanography》1977,33(4):190-198

Measurements of local values of the skin friction have been made at many points along the surface of representative wind wave crests in a wind wave tunnel, by use of the distortion of hydrogen-bubble lines. The results obtained at 2.85-m fetch under 6.2 m s^–1 mean wind speed show that the intensity of the skin friction varies greatly along the surface of wind waves as a function of the phase angle. It increases rather continuously at the windward surface toward the crest, attains a value of about 12 dyn cm^–2 near the crest, decreases suddenly just past the crest, and the value at the lee surface is substantially zero Values of the skin friction thus determined along the representative wind waves give an average value of 3.6 dyn cm^–2, rather exceeding the overall stress value of 3.0 dyn cm^–2, which has been estimated from the wind profile. The results are interpreted as that the skin friction bears most of the shearing stress of wind, and that it exerts most intensively around the representative wave crests at their windward faces.  相似文献   

Field data support of three-seconds power law andgu *σ−4-spectral form for growing wind waves     

Sanshiro Kawai  Kozo Okada  Yoshiaki Toba 《Journal of Oceanography》1977,33(3):137-150

Observational data on air-sea boundary processes at the Shirahama Oceanographic Tower Station, Kyoto University, obtained in November, 1969, was analyzed and presented as an example representing the structure of growing wind-wave field. The condition was an ideal onshore wind, and the data contained continuous records of the wind speed at four heights, the wind direction, the air and water temperatures, the tides, and the growing wind waves, for more than six hours. The main results are as follows. Firstly, in both of the wind speed and the sea surface wind stress, rather conspicuous variations of about six-minute period were appreciable. Secondly, the three-seconds power law and its lemma expressed byH ^*=BT ^*3/2 and=2BT ^*–1/2, respectively, are very well supported by the data, whereH ^*(gH/u _* ²) andT ^*(gT/u _*) are the dimensionless significant wave height and period, respectively, the wave steepness,u _* the friction velocity of air,g the acceleration of gravity, andB=0.062 is a universal constant. Thirdly, the spectral form for the high-frequency side of the spectral maximum is well expressed by the form of()= _sgu_*^–4, where is the angular frequency and() the spectral density. The value of _s is determined as 0.062±0.010 from the observational data. There is a conspicuous discrepancy between the spectral shape of wind waves obtained in wind-wave tunnels and those in the sea, the former containing well-defined higher harmonics of the spectral peak, and consequently there is an apparent difference in the values of _s also. However, it is shown that the discrepancy of _s may be eliminated by evaluating properly the energy level of the spectral form containing higher harmonics.  相似文献   

Dynamics of estuarine residual circulation in a narrow channel including tidal-nonlinear effects     

Yoshiaki Shiraki  Tetsuo Yanagi 《Journal of Oceanography》2007,63(3):413-425

Numerical modeling of a semienclosed narrow channel demonstrates the dynamical dependency of an estuarine residual circulation (ERC) on tidal amplitudes. The ERC is defined by tidally-averaged current field. The tidally-averaged fields show that the ERC-strength variation is classified into highly stratified, partially stratified and weakly stratified ranges, respectively. The ERC becomes weaker as the tidal amplitude (and hence vertical mixing) increases in the highly and weakly stratified ranges. However, the ERC becomes stronger oppositely in the partially stratified range. The nonlinear forces induced by tides significantly affect the ERC as well as the pressure gradient force due to the freshwater flux and the vertical stress divergence (vertical eddy viscous force). In particular, the tidal stress and tidally-oscillating component of vertical stress divergence are quite important in ERC dynamics. The latter causes the enhancement of ERC in proportion to the vertical mixing in the partially stratified range.  相似文献   

Spin-up and spin-down processes of the large cold water mass of the Kuroshio south of Japan     

Yoshihiko Sekine  Haruo Ishii  Yoshiaki Toba 《Journal of Oceanography》1985,41(4):207-212

Time variation of the cold water mass of the Kuroshio south of Japan, which was formed in August 1975 and disappeared in August 1980, is studied. Its lifecycle includes several repetitions of spin-down and spin-up processes. The spin-down (or the spin-up) process is accompanied by warming (cooling) of the cold water mass and descending (ascending) motion of the inner water. Expansion of the cold water area is also associated with the spin-up period while shrinking occurs in the spin-down period. The rate of spin-down of the cold water mass is approximately equal to that of the Gulf Stream rings. The spin-up process is not observed in the Gulf Stream rings and the longer lifetime of the cold water mass off Japan, in comparison with the Gulf Stream rings, is due to the existence of the spin-up periods. The spin-up process tends to occur in late spring to summer, and it seems to be related to the seasonal variation in intensity of the Kuroshio.  相似文献   

Contemporary crustal deformations in the Izu peninsula,Honshu, Japan and acceleration of plate bending in the northernmost part of the Philippine Sea plate     

Yoichiro Fujii 《Pure and Applied Geophysics》1991,136(2-3):315-341

Since the beginning of the anomalous vertical crustal movement in the Izu peninsul, Honshu, Japan, many repeated precise levellings have been carried out by the Geographical Survey Institute. Trilaterations covering the entire Izu peninsula have also been carried out by the Geographical Survey Institute. A new technique is developed to adjust the results of levellings, because they had been carried out for different epochs along each levelling route and because of rapid vertical crustal movements. In conventional least-squares adjustment of levelling network, only corrections to the approximate height are assumed to be unknown, while in the present analysis a special model in which rates of vertical deformation at any bench marks are also assumed to be unknown, is adopted. In addition, tidal stations along the coast of the Izu peninsula yield the rate of vertical crustal movement from analysis of tidal data independent of levelling data. We select several special bench marks in which rates of vertical movement are determined by tidal analysis, thereafter special adjustment is applied according to the type of network.The results show that the peninsula is inclined to the south-west. Uplift in the northeastern part of the peninsula is accompanied by remarkable subsidence in the southwest. The rate of contemporary inclination is many times higher than the rate during the period from 1929 to 1972.The deformation is concentrated in the area whereNakamura (1979, 1980) pointed out the bending of the Philippine Sea plate. The mode and rate of the detected crustal deformation suggest the accelerated bending of the peninsula. There are some local uplift that deviate from the general pattern of deformation. The most remarkable land uplift was observed near Ito, a city within the peninsula, and the focus of this uplift migrated with time. The accelerated plate bending will produce an extension at the earth's surface and contraction in the deeper part of the subcrustal layer, additionally it triggered the intrusion of magma from the deeper part to the shallower. Moreover, the accelerated plate bending also triggered seismic swarms and destructive, earthquakes in and around the peninsula.  相似文献   

Inventory of perennial snow patches in Central Japan     

Prof. Dr. K. Higuchi  T. Iozawa  Dr. Y. Fujii  H. Kodama 《GeoJournal》1980,4(4):303-311

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Rayleigh wave scattering at wedge corners with major wedge angles     

Masayoshi Nakano  Kazunari Fujii  Shozaburo Takeuchi 《Pure and Applied Geophysics》1988,128(1-2):119-132

Theoretical calculations were performed on reflected and transmitted Rayleigh waves and scattered body waves, in the case where a two-dimensional Rayleigh wave is incident to a wedge-shaped medium having a wedge angle between 250° and 290° and arbitrary value of Poisson ratio. The reflection and transmission coefficients of Rayleigh waves were also experimentally measured in cases of wedges with 190° to 330° wedge angles. The method of theoretical analysis and the techniques of experiment are based on those developed in our preceding research (W-1. W-2 and W-3). Compared with the results where the wedge angle is smaller than 180° (W-1 and W-2), all features show consistent variation with wedge angle.  相似文献   

On “the upward transport of sediment by time-varying current”     

Masahiro Kajihara  Katsuhiko Matsunaga  Yoshiaki Maita 《Journal of Oceanography》1975,31(5):216-218

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Possible future trends in the study of global climate system and the “Journal of Oceanography”     

Yoshiaki Toba 《Journal of Oceanography》1992,48(1):1-4

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Forced convection accompanying wind waves     

Yoshiaki Toba  Masayuki Tokuda  Kuniaki Okuda  Sanshiro Kawai 《Journal of Oceanography》1975,31(5):192-198

Wind-wave tunnel experiments reveal, by use of techniques of the flow visualization, that wind waves are accompanied by the wind drift surface current with large velocity shear and with horizontal variation of velocity relative to the wave profile. The surface current converges from the crest to a little leeward face of the crest, making a downward flow there, even though the wave is not breaking. Namely, wind waves are accompanied by forced convections relative to the crests of the waves. Since the location of the convergence and the downward flow travels on the water surface as the crest of the wave propagates, the motion as a whole is characterized by turbulent structure as well as by the nature of water-surface waves. In this meaning, the term of real wind waves is proposed in contrast with ordinary water waves. The study of real wind waves will be essential in future development of the study of wind waves.  相似文献