Some remarks on the spectrum of rapid-changing random data in the ocean     

Hideo Nakajima 《Journal of Oceanography》1984,40(5):367-370

Spectral characteristics of rapid-changing random data in the ocean are discussed. Analysis shows that, if records are approximated by saw-toothed random series ₁ and step series ₂, ₁ and ₂ generally have spectral ranges of the –4th power and –2nd power, respectively, with respect to frequency (or wave number).  相似文献   

Scale dependence of divergence and vorticity of near-surface flows in the sea     

Hideo Kawai 《Journal of Oceanography》1985,41(3):157-166

To area-average the horizontal divergence and the vertical component of vorticity, three methods are proposed and examined. The polygon method is based on deformations of a polygon made by connecting drifters. They are deployed at widely different scales of 1 cm^– 1,000 km and tracked using various procedures. The loop method is adopted when a drifter completes at least two loops of trajectory in a tidal vortex, a ring or a gyre. Even if data for a drifter completing only one loop is available, the vorticity can be calculated. The crossing method is applied to the GEK data on the circumference of a Kuroshio ring. The data which will be used to calculate them in Part 2 are summarized in tables. Offset dispositions of positive and negative divergences or vorticities on a horizontal plane and in a water column are shown. Probably, the vertical offset of vorticities does not occur in general. The area-turnover of a polygon of drifters are discussed. Sampling time-intervals, appropriate to the scale of the area, for the polygon and loop methods are examined. A first impression of Rhines' (1979) sketch has produced a misunderstanding that the polygon method would be useless because a limited number of drifters cannot follow such a complicated deformation of the material line over a long period. It is shown that adopting a short time-scale appropriate to the length scale furnishes a practical solution to the problem.  相似文献   

Interpretation of Repulsive Bifurcation of the Kuroshio and Gulf Stream with Classification of Their Branches     

Hideo Kawai 《Journal of Oceanography》2003,59(3):303-315

Distinctive features of the repulsive bifurcation of Kuroshio and Gulf Stream jets, induced from various observations, have been examined by equations of motion of a 1 1/2 -layer model in natural coordinates, although causes of the bifurcation are discussed little. From the conservation of volume flux through paths above a main thermocline, we have derived the equation M _n K _In + M _s K _Is = 0 for northern (n) and southern (s), steady-state curved jets, just downstream of the bifurcation from a straight jet, where M is momentum flux through the path and K _I, positive for cyclonic deflection of the streamline, is the curvature of a certain intermediate streamline in the laminar path. Assuming concentric streamlines in the curved path, which is narrower than 1–0.5 times the radius of curvature of the center streamline of the path, and symmetric momentum flux through a path element of unit width with respect to the center streamline, we found that K _I approximates to the curvature averaged across the path, relative errors being <0.25−(0.25)². Bifurcation starts with a ‘Big Bang’ and the leading turbulent front of a split jet may be unsteady, but the succeeding laminar part can be regarded as stationary or as translating at a constant velocity, as if frozen. Thus, such features are described by the equation. A provisional classification is given of various warm extrusions along branches of both Streams, all of which exemplify the repulsive bifurcation, except for the mainstreams with very narrow (< 30–40 km) branches, possibly due to misapplication of the model. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Influence ofNoctiluca's predation on theAcartia population in Ise Bay,central Japan     

Hideo Sekiguchi  Takashi Kato 《Journal of Oceanography》1976,32(5):195-198

The influence ofNoctiluca's predation on theAcartia population in Ise Bay was examined by taking samples at 27 stations once a month from May to December, 1974.The copepod eggs were found inNoctiluca mainly in May and June. Considering from various spawning types of copepods, the eggs were presumed to beAcartia, the most numerous species of all copepods in the bay.Noctiluca was dominant plankton in May and June whenAcartia was abundantly distributed.Acartia eggs were found in 33.2–39.3% of individuals ofNoctiluca in May and June.Noctiluca was more frequently observed to contain one egg ofAcartia per individual. It was suggested that 55.0 eggs perAcartia female per day were eaten by theNoctiluca population in May wherease 3.5 eggs in June. It was deduced that 74% of the eggs produced byAcartia was preyed on byNoctiluca (about 5% in June). The predation byNoctiluca as well as that by the sand-eel must influence greatly to the production ofAcartia in the bay.  相似文献   

Circulation pattern and current variations with respect to tidal frequency in the sea near the head of Suruga Bay     

Hideo Inaba 《Journal of Oceanography》1981,37(4):149-159

Current measurements were conducted 10 m below the sea surface near the head of Suruga Bay intermittently from 1970 to 1978. The circulation pattern is usually counterclockwise; northward along the east coast (off Heda and at the mouth of Uchiura Inlet), westward along the north coast (off Fuji), and southwestward along the west coast (off Shimizu). The amplitudes of the four major tidal constituents of current variation, M₂, S₂, K₁ and O₁, are much larger than those expected from sea level variations along the coast. The amplitudes of the diurnal constituents of current variation are much larger than those of the semidiurnal constituents, while the amplitudes of the semidiurnal constituents of sea level variation are much larger than those of the diurnal constituents. The observed amplitude of the predominant diurnal constituents exhibit large seasonal changes and tend to increase with the development of the stratification of the upper part of the water in Suruga Bay. These facts strongly suggest that the observed current variations are mainly associated with internal tides in Suruga Bay.  相似文献   

Thermohaline staircases in the Warm-Core Ring off Cape Erimo,Hokkaido and their fluxes due to salt finger     

Hideo Miyake  Seiji Sasaki  Hidekazu Yamaguchi  Kiyoshi Masuda  Gen Anma  Yoshihiko Kamei 《Journal of Oceanography》1995,51(1):99-109

Thermohaline staircases off Cape Erimo, Hokkaido are described and their physical properties are compared with those in other seas. The mean fluxes for heat and salt across the interface induced by salt finger were estimated as 105 cal cm^–2d^–1, and 0.03 g cm^–2d^–1, respectively. These values were in the same order as those in Caribbean Sea. The effective eddy diffusivities were also in the same order as the Caribbean ones. This suggests that the double-diffusive convection plays on important role on the water mass conversions occurring in the interfrontal zone between the Oyashio and the Kuroshio Waters.  相似文献   

Distribution of scyllarid phyllosoma larvae (crustacea: decapoda: scyllaridae) in the Kuroshio subgyre     

Nariaki Inoue  Hideo Sekiguchi 《Journal of Oceanography》2007,63(1):160-160

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Large-scale ripple marks on the shelf margin of the Northern Okinawa Trough     

Hideo Kagami  Shigeaki Kubo  Noriyuki Nasu 《Journal of Oceanography》1984,40(3):230-242

Trains of large-scale ripple marks (megaripples and sand waves) were found on the Amakusa and East China Sea shelves bordering the northern Okinawa Trough. Side-scan sonar surveys were carried out in 1974 and 1976 to investigate sea-floor features lying along a proposed submarine cable line. Megaripples were found on the outer margin of the Amakusa shelf between depths of 140 and 200 m. The megaripples were especially well developed at a depth of 167 m. They were typically straight-transverse crested with asymmetrical profiles, and measured 7 to 15 m in wavelength and 0.4 to 1.4 m in waveheight. Formation of the megaripples on the Amakusa shelf is probably controlled by relatively complex oceanographic conditions. A secondary circulation associated with the Gotô-nada clock-wise Current may be responsible for formation of the ripple marks. Local vorticities generated in the coastal boundary layer as a result of curvature of the Gotô-nada Current are known to cause the complex flow pattern at the Gotô and Amakusa shelf margins. The main semidiurnal (M₂) tidal current may also interact with these fluid processes.On the East China Sea shelf, megaripples and sand waves were found between depths of 140 and 220 m. Sand waves (200 m in wavelength) were observed in seismic reflection profiles. Large-scale lunate megaripples were observed at a depth of 154 m by the side-scan sonar. They had wavelengths of 10 to 30 m and waveheights of 1 to as high as 3 m. It appears from the types and nature of distribution of the megaripples that they are responding to the present-day flow regime, and it is partly ascertained from our observations over an interval of two years that the megaripples appear to be short-term response elements compared wit hteh sand waves. We conclude that the megaripples on the East China Sea shelf are current-formed during peak typhoon flow in August to November. From their distribution, the long term path of the main flow of the Tsushima Current is inferred at the edge of the East China Sea shelf. An area of low sediment mud content (less than 20 per cent) coincides with this path giving further support to our interpretation.  相似文献   

Spatial Distributions of Phyllosoma Larvae (Crustacea: Decapoda: Palinuridae and Scyllaridae) in Taiwanese Waters     

Nariaki Inoue  Hideo Sekiguchi  Shinn-Pyng Yeh 《Journal of Oceanography》2001,57(5):535-548

Distributions and taxonomy of phyllosoma larvae were examined in Taiwanese waters, based on ichthyoplankton samples collected from May 1990 to July 1995. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae representing 6 genera and 13 species. Of the collected phyllosoma larvae, those of Scyllarus and Panulirus species were most abundant, forming 90% of total numbers. Early stage Scyllarus and Panulirus phyllosoma larvae were abundant in Taiwanese waters. Middle to late stages (except the final stage) of Panulirus phyllosoma larvae were absent from the waters throughout the year, while those of Scyllarus phyllosoma larvae were collected in the waters. This suggests that all stages of Scyllarus phyllosoma larvae may be retained in the northern part of the waters around northern Taiwan while middle to late stages of Panulirus phyllosoma larvae may be flushed out from the waters, the sub-final and final stages then possibly returning to the waters. An anticlockwise eddy existed in the waters off northeastern Taiwan, which may be closely related to flushing out and returning of Panulirus phyllosoma larvae through a much longer planktonic period. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Vertical Distributions of Phyllosoma Larvae of Palinurid and Scyllarid Lobsters in the Western North Pacific     

Hideki Minami  Nariaki Inoue  Hideo Sekiguchi 《Journal of Oceanography》2001,57(6):743-748

Vertical distributions of phyllosoma larvae were examined in waters east of the Philippines or west of the Mariana Islands (18°56′ N to 19°04′ N; 129°10′ E to 129°35′ E) based on zooplankton samples collected with an Isaacs-Kidd Midwater Trawl on September 22–24, 1986. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae comprising 4 genera and 9 species. Of the collected phyllosoma larvae, those of Scyllarus cultrifer and Panulirus longipes were most abundant and showed similar vertical distributions: (1) both species were collected from the mixed layer at night but not in the day, (2) their vertical distributions did not change with their stages, and (3) the upper limit of their vertical distributions during the day accorded with the base of mixed layer. Furthermore, their vertical distributions were similar to those of lepthocephalus larvae which were collected using the same sampling stations and gear in the present study. Vertical distributions of phyllosoma larvae were discussed in relation to their horizontal distributions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献