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Volume 40, Issue 1
Displaying 1-9 of 9 articles from this issue
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Part 1. Probability Density Distribution of Surface ElevationMitsuhiko Hatori1984 Volume 40 Issue 1 Pages 1-11
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSNonlinear properties of wind waves in a wind-wave tunnel are investigated bymeasuring the probability density distribution of surface elevation. The surface elevationdistribution of raw records are found to have a positive skewness (K3=0.21 to 0.43) and anegative kurtosis (K4=-0.74 to -0.41) with magnitude depending of fetch and wind speed.The values of skewness are in qualitative agreement with a prediction of the weak interactiontheory for a random wave field incorporating the effects of second harmonics (Tayfun, 1980), but the values of kurtosis are different in sign from the prediction.
To examine the nonlinear properties of energy containing components, higher harmoniccomponents are excluded from the wave records by using a kind of a band-pass filter. Thesurface elevation distributions of the filtered waves show a sharp decrease in skewness (K3'=0), but the distributions remain highly non-Gaussian with a large negative kurtosisalmost independent of the fetch and wind speed (K4'=-0.66). It is concluded that thenegative kurtosis is due to the non-random character of the phase and amplitude among theenergy containing components, and that nonlinear interactions occur amongst the energycontaining frequencies.View full abstractDownload PDF (1720K) -
Part 2. Detailed Structures of Power Spectra and their Evolution with FetchMitsuhiko Hatori1984 Volume 40 Issue 1 Pages 12-18
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe fine structure of wind-wave spectra in a wind-wave tunnel is investigated inconnection with the process of nonlinear interaction among spectral components, where eachspectrum is calculated from about one hour of data measured with 8 wave gauges arrangedat a distance of 25 cm. It is found that there are several significant spikes, or primary modes, around the spectral maximum fo. Among such primary modes, three primary modes includingthe spectral maximum satisfy the resonance condition 2f0=f1-F-f2, where fi and f2 are frequenciesof the higher and lower frequency modes adjacent to fo, while the frequency widthbetween adjacent modes, f1-f0 or f0-f2, is nearly equal to 0.1 f0. In the process of growthof the spectra with fetch, the energy density at the lower frequency f2 increases accompaniedwith an energy decrease at the higher frequency f1, and the mode f2 replaces the mode foas the spectral maximum. This evolutional process is repeated several times in the range ofthe present experimental condition. These results suggest that the discrete primary modesare not due to statistical error, but rather due to some wave-wave interaction.View full abstractDownload PDF (1013K) -
Yoshihiro Mazda1984 Volume 40 Issue 1 Pages 19-28
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe process of material transport through a strait due to tidal flow is modeled, and then the differences between various concepts of tidal exchange which have been usedhitherto are pointed out using this model. In particular, the exchange of water itself andthe exchange of material should be distinguished even in the case where the material ofinterest is carried by the water, i.e., the material and water move as one body. Further, the physical meaning of “tidal trapping” (Fischer et al., 1979) is discussed by using the modelin this paper. The relationship between the exchange ratio for the water itself (r) and thephase lag (δ) of material concentration to the tidal stream in a section of the strait, whichis an important factor in tidal trapping, is obtained as follows:
δ=tan-1 (1/r-1).
Observational results at Lake Hamana (Shizuoka Pref.) and at Kabira Cove (Okinawa Pref.) support the validity of the above relationship.View full abstractDownload PDF (1556K) -
Momoki Koga1984 Volume 40 Issue 1 Pages 29-38
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThis paper describes the dispersal of droplets over breaking wind waves underthe direct action of wind, based on a comparison between the actual distribution of dropletvelocity and the wind field measured in a wind-wave tank reference wind speed 16m sec-1 The velocity distribution of droplets with a diameter d>0.81mm over breaking wind waveswas measured by Koga (1981). In this paper the wind field over breaking wind waves ismeasured by a flow visualization technique using styrofoam flakes as a tracer. The comparisonallows a clear interpretation of droplet movement over the wave profile, and shows that thehorizontal movement of the droplets of d>0.81mm is approximately determined by accelerationby the wind while their vertical movement is determined by acceleration due to gravity.These observations offer some support for the dispersion model proposed by Koga and Toba (1981).View full abstractDownload PDF (3350K) -
Shiro Imawaki, Keisuke Taira, Toshihiko Teramoto1984 Volume 40 Issue 1 Pages 39-45
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSA set of simultaneous long-term, deep current measurements was taken using amoored array in the mid-ocean of the western North Pacific near 30°N, 146°E. Five currentmeters at three stations provided good quality records over 84 days. Low-frequency currentfluctuations with meridional dominance are clearly seen in the deep layer records. They areconsistent with signals of a mesoscale current fluctuation which has a period of about 100days, an east-west wave length of about 200 km, and a westward phase propagation with aspeed of about 2cm sec-1. Bottom intensification of the east component of low-frequencycurrent fluctuations is also observed.View full abstractDownload PDF (1032K) -
Part 4. The Generation of Flow in Excess of the Phase SpeedKuniaki Okuda1984 Volume 40 Issue 1 Pages 46-56
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe minimum value of wind stress under which the flow velocity in short windwaves exceeds the phase speed is estimated by calculating the laminar boundary layer flowinduced by the surface tangential stress with a dominant peak at the wave crest as observedin previous experiments. The minimum value of the wind stress is found to depend stronglyon β, the ratio of the flow velocity just below the boundary layer and the phase speed, butweakly on L, the wavelength. For wind waves previously studied (β=0.5, L=10cm), theexcess flow appears when the air friction velocity u is larger than about 30cm sec-1. Thepresent results confirm that the excess flow found in my previous experiments is associatedwith the local growth of a laminar boundary layer flow near the wave crest.View full abstractDownload PDF (1909K) -
Yuichi Hirotat, Takahisa Nemoto, Ryuzo Marumo1984 Volume 40 Issue 1 Pages 57-66
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe larvae of Euphausia similis G. O. Sars in Sagami Bay, Central Japan, aredescribed. Nauplius, metanauplius, calyptopis and furcilia stages are included. In the furciliastage, six forms are identified on the basis of the form of the pleopods and the number ofterminal telson spines. Furcilia I: a pair of non-setose pleopods and seven terminal telsonspines. Furcilia II: a pair of setose and three pairs of non-setose pleopods and seven terminalspines. Furcilia III: four pairs of setose and a pair of non-setose pleopods and seventerminal spines. Furcilia IV: five pairs of setose pleopods and five terminal telson spines.Furcilia V: five pairs of setose pleopods and three terminal telson spines. Furcilia VI: fivepairs of setose pleopods and one terminal telson spine. On the basis of the developmentalpathway of the larvae, E. similis is suggested to be related to E. spinifera, E. longirostris, E. hanseni and the E. gibboides group species. The size of E. similis larvae, expressed astotal length, in Sagami Bay varied according to month. The sizes of calyptopis III and furciliaI-V stages were smallest in November and March and largest in May.View full abstractDownload PDF (4505K) -
Hideo Miurat, Nobuo Suginohara1984 Volume 40 Issue 1 Pages 67-79
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSVariations of the western boundary currents induced by a periodic change in windstress are studied in a two-layer model with a continental slope along the western boundary.The variation of the total transport of the western boundary current over the continental slopeshows a considerable phase lag with the wind stress and a decrease in amplitude comparedwith for the flat bottom ocean, though the interior barotropic response is to adjust almostinstantaneously to the wind stress. The total transport variation of the western boundarycurrent is well approximated by the upper layer transport variation. That is, almost completeseparation of the upper- and lower-layer flows takes place over the slope, and only the upperlayer flow contributes to the change in total transport of the western boundary current.Contributions of the interior barotropic and baroclinic responses to the upper layer transportvariation depend on the forcing period. With decrease in the forcing period, the barotropicresponse becomes relatively important for determining the upper layer transport variationalthough the amplitude of the variation is smaller.View full abstractDownload PDF (1932K) -
Satoshi Yamamoto1984 Volume 40 Issue 1 Pages 80-89
Published: February 25, 1984
Released on J-STAGE: June 17, 2011
JOURNAL FREE ACCESSThe pattern of distribution of detrital mineral grains in the water column wasinvestigated at three stations in the western Pacific during July through August of 1979.The sedimentation of detrital mineral grains was also studied using piston cores from twosites adjacent to the three stations. The concentration of suspended detrital mineral grainsin the subsurface waters becomes lower with increasing distance from the land, and shows aprominent peak in the intermediate zone of the water column. The sharp increase in waterdensity and viscosity in the pycnocline in the intermediate zone decreases the settling velocityof grains, and may result in the accumulation of falling grains in the intermediate layer.Proportion of detrital mineral grains to organic remains in the sediment was more than twoorders of magnitude larger than in the overlying water column, and reasons for this arebriefly discussed.View full abstractDownload PDF (1363K)
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