Tidal transport through the Tsugaru Strait — part I: Characteristics of the major tidal flow and its residual current     

Quang-Hung Luu  Kosuke Ito  Yoichi Ishikawa  Toshiyuki Awaji 《Ocean Science Journal》2011,46(4):273-288

The potential role of the tide-induced time-mean flow (the tidal residual current) in determining transport through the Tsugaru Strait (located between the East/Japan Sea and the North Pacific) is investigated using a high-resolution numerical barotropic model. The calculated K₁, O₁, M₂, and S₂ tidal fields agree well with available observational records derived from both tide gauge and current meter measurements in the strait and the adjacent seas. The tidal residual current speed reaches 0.3 ms⁻¹ in two narrow “neck” areas where topographic sills are located. This result suggests that tides should be taken into account in estimating the long-term water mass and nutrient transport through narrow regions between the East/Japan Sea and the North Pacific. An interesting aspect of the tidal residual current field is the prediction of several active eddy zones in which sequences of eddy triplets develop in the vicinity of capes. Our vorticity analysis reveals that the interplay of topographic effects arising from both the headland and the sill around capes plays a critical role in the formation of these triple eddy patterns.  相似文献   

River Water Pollution in Developed and Developing Countries: Judge and Assessment of Physicochemical Characteristics and Selected Dissolved Metal Concentration   总被引：1，自引：0，他引：1  

M. Tajuddin Sikder  Yusuke Kihara  Masaomi Yasuda  Yustiawati  Yoshihiro Mihara  Shunitz Tanaka  Dalkhjav Odgerel  Badamtsetseg Mijiddorj  Suhaemi M. Syawal  Toshiyuki Hosokawa  Takeshi Saito  Masaaki Kurasaki 《洁净——土壤、空气、水》2013,41(1):60-68

To compare water quality in rivers of developed and developing countries, a study based on physicochemical parameters and dissolved metals levels was conducted. Water samples were collected from selected sites in Dhaka, Bangladesh; Hokkaido and Osaka, Japan; Erdenet, Mongolia and West Java, Indonesia. Analysis of least significant differences revealed that most water quality parameters were within comparable low levels in both developed and developing countries. The dissolved metals concentrations were found to be similar and below those of water standards except for manganese and cadmium at every sampling point, and lead in Erdenet, Mongolia. Some metals showed high enrichment factors in the rivers of Osaka, Japan and Erdenet, Mongolia, indicating accumulation possibility of metals in the river‐bed sediments. High concentrations of dissolved organic carbon, Escherichia coli and dissolved metals suggested greater water pollution in some rivers of developing countries than in the rivers of Japan. Principal component analysis showed strong correlations between “dissolved organic carbon and chemical oxygen demand” and “conductivity and total dissolved solids” at each sampling point, and E. coli, nitrate (NO), nitrite (NO), and pH levels were found to be higher in the rivers of Dhaka and Erdenet. In addition, there were high levels of Al and Zn in West Java, Pb in Erdenet, and Mn, Fe, and Cr in the rivers of Dhaka and Japan. Based on pressures and impacts, it is evident that dissolved metal, organic, and fecal pollution in the rivers of developing countries are in somewhat dreadful condition in comparison with the rivers of developed country.  相似文献   

Estimation of canopy drying time after rainfall using sap flow measurements in an emergent tree in a lowland mixed‐dipterocarp forest in Sarawak,Malaysia     

Tomonori Kume  Koichiro Kuraji  Natsuko Yoshifuji  Toshiyuki Morooka  Shinji Sawano  Lucy Chong  Masakazu Suzuki 《水文研究》2006,20(3):565-578

This study emphasizes the importance of canopy drying time (CDT) after rainfall in a lowland tropical rain forest. In this study, we estimate CDT using sap flow velocities measured by a heat‐pulse method in an emergent tree in a lowland mixed‐dipterocarp forest. Estimated CDT (ECDT) for each rain event has been defined as the time from rainfall cessation to the specific time derived from the difference between diurnal courses of sap flow velocities on a rainy day versus bright days. ECDT could be derived for 22 rain events that were grouped into two types, depending on whether rainfall ceased before or after noon. The ECDTs were distributed more widely and with greater values when rainfall ceased before noon (Type 1) than after noon (Type 2). The ECDTs of both Type 1 and Type 2 decreased with increases in net radiation (Rn) and vapour pressure deficit (VPD) after rainfall. This result shows that ECDT is determined mainly by post‐rainfall evaporation rates. The sap flow velocity as a detector of canopy wetness worked out well because of the specific rainfall characteristics at this site. The practical limitations of the method using sap flow velocities are discussed in relation to rainfall characteristics and time lags between transpirations and sap flow velocities. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Step-like structure in temperature and salinity profiles,observed near icebergs trapped by fast ice,Antarctica     

Kay I. Ohshima  Toshiyuki Kawamura  Takatoshi Takizawa  Shuki Ushio 《Journal of Oceanography》1994,50(3):365-372

Step-like thermohaline structure was observed near icebergs trapped by fast ice in Lützow-Holm Bay, Antarctica. The structure was developed within the draft depth of the icebergs. The typical vertical distance between the succeeding step surfaces is 20–30 m, and the temperature and salinity differences across the step surface are about 0.05–0.06 deg and 0.06–0.10 psu, respectively. The structure appears to be generated by a sea-water/iceberg interaction, and is explainable by a simple model in which an ice wall is placed in the ocean linearly stratified by vertical salinity gradient.  相似文献   

Tidal exchange through Naruto,Akashi and Kitan Straits     

Norihisa Imasato  Toshiyuki Awaji  Hideaki Kunishi 《Journal of Oceanography》1980,36(3):151-162

In order to re-evaluate the water volume exchange through Naruto Strait, we have performed a numerical experiment (nonlinear barotropic model including the actual depth of water and the details of shoreline) where trajectories of a number of labeled particles are calculated during a full cycle of the M₂ tidal current. The ratio of water volume exchanged through Naruto Strait to that through Akashi Strait is found to be twice as large as the previously estimated value. The calculated water exchange rate is 104 % for Naruto Strait, 52 % for Akashi Strait and 28 % for Kitan Strait. In the case where the tide-induced residual current is excluded from the calculated velocity field (i.e. considering only the M₂ current), the calculated exchange rate maintains the level of 68 % for Naruto Strait, 18 % for Akashi Strait and 11 % for Kitan Strait, respectively. The mechanism of tidal exchange through these three straits is discussed, and it is shown that a suitable exchange rate is obtained by starting the calculation of trajectories of labeled particles at the time of either a maximum ebb- or flood-current.  相似文献   

Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field   总被引：2，自引：0，他引：2  

Watanabe  Michio  Hibiya  Toshiyuki 《Journal of Oceanography》2005,61(1):123-127

Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10⁻⁹ W kg⁻¹. This corresponds to a diapycnal diffusivity of about 0.3 × 10⁻⁴ m²s⁻¹, which is less than the value 10⁻⁴ m²s⁻¹ required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10⁻⁴ m²s⁻¹. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean.  相似文献   

A dispersion equation and dispersion coefficient for material transport in Inland Seas     

Toshiyuki Awaji  Hideaki Kunishi 《Journal of Oceanography》1983,39(1):1-8

To analyse material transport in inland seas, a horizontal two-dimensional dispersion equation is derived, and the dispersion coefficient due to the combined effect of vertical turbulent mixing and vertical shear of both a steady current and a tidal current is studied. In the present study, the assumption that velocity is uniform in horizontal planes is not necessary, and velocity has a free vertical profile; thus the dispersion coefficient formulated is general, and is represented by a tensor of the second order. The properties of the dispersion coefficient in the horizontal two-dimensional dispersion model are also investigated, and it is shown that the time-averaged dispersion coefficient due to the tidal current over a tidal period is approximately half that due to the steady current, if the velocity amplitude and the vertical profile of the tidal current are the same as those of the steady current (a similar result was presented byBowden (1965) for horizontal one-dimensional models). Finally, the dispersion coefficient in Hiuchi-Nada (Hiuchi Sound) in the central part of the Seto Inland Sea is evaluated by using the model. The values of the dispersion coefficient in that region range from 10³ cm² s^–1 to 10⁵ cm² s^–1 when vertical turbulent diffusivity is taken to be 50 cm² s^–1.  相似文献   

Pb and Cs in sediments from Sagami Bay, Japan: sedimentation rates and inventories     

Y Kato  H KitazatoM Shimanaga  T NakatsukaY Shirayama  T Masuzawa 《Progress in Oceanography》2003,57(1):77-95

Profiles of the radioisotopes ²¹⁰Pb and ¹³⁷Cs were determined in 15 sediment cores collected from Sagami Bay, Japan. The activities of ²¹⁰Pb_ex (unsupported) in core top sediments increased with water depth from 25 dpm g⁻¹ on the upper continental slope off the mouth of Tokyo Bay to an average of 283 dpm g⁻¹ at the deep-sea station SB. The high ²¹⁰Pb trapping efficiency of settling particles expected from the results of the sediment trap experiment near the SB site suggests that effective ²¹⁰Pb enrichment in surface sediments may occur during resuspension and lateral transportation of particles via the benthic nepheloid layer on the continental slope. In several cores, ¹³⁷Cs profiles showed an increase, a distinct peak, and then a decrease to an undetectable level downcore. These profiles can be compared with the temporal change of bomb-produced ¹³⁷Cs fallout.The mean sedimentation rates estimated by the ²¹⁰Pb_ex inventory method, rather than using ²¹⁰Pb_ex profiles, ranged from 0.06 g cm⁻² y⁻¹ to 0.14 g cm⁻² y⁻¹. The average value of the rates in SB cores was calculated to be 0.11 g cm⁻² y⁻¹, which was similar to that calculated under the assumption that the age of the ¹³⁷Cs peak corresponds to its maximum fallout year in 1963.Although ¹³⁷Cs inventories represented one tenth of the anthropogenic fallout of ¹³⁷Cs until 1997, they correlated with the increase in ²¹⁰Pb_ex inventory. This suggests that the scavenging of refractory ¹³⁷Cs as well as ²¹⁰Pb by settling particles in the water column can lead to the formation of a time marker layer even in deep-sea sediment core, such as at the SB site.  相似文献   

Numerical Study of the Generation and Propagation of Trigger Meanders of the Kuroshio South of Japan     

Takahiro Endoh  Toshiyuki Hibiya 《Journal of Oceanography》2000,56(4):409-418

We examine the processes underlying the generation and propagation of the small meander of the Kuroshio south of Japan which occurs prior to the transition from the non-large meander path to the large meander path. The study proceeds numerically by using a two-layer, flat-bottom, quasi-geostrophic inflow-outflow model which takes account of the coastal geometries of Kyushu, Nansei Islands, part of the East China Sea, and the Izu Ridge. The model successfully reproduces the observed generation and propagation features of what is called "trigger meander" until it passes by Cape Shiono-misaki; presumably because of the absence of the bottom topography, the applicability of the present numerical model becomes questionable after the trigger meander passes by Cape Shiono-misaki. The generation of the trigger meander off the south-eastern coast of Kyushu is shown to be associated with the increase in the supply of cyclonic vorticity by the enhanced current velocity in the upper layer along the southern coast of Kyushu where the no-slip boundary condition is employed. Thereafter, the trigger meander propagates eastward while inducing an anticyclone-cyclone-cyclone pair in the lower layer. The lower-layer cyclone induced in this way, in particular, plays a crucial role in intensifying the trigger meander trough via cross-stream advection in the upper layer; the intensified trigger meander trough then further amplifies the lower-layer cyclone. This joint evolution of the upper-layer meander trough and the lower-layer cyclone indicates that baroclinic instability is the dominant mechanism underlying the rapid amplification of the eastward propagating trigger meander.  相似文献   

Unconformity between a Late Miocene–Pliocene accretionary prism (Nishizaki Formation) and Pliocene trench‐slope sediments (Kagamigaura Formation), central Japan     

Yuzuru Yamamoto  Shun Chiyonobu  Toshiyuki Kurihara  Asuka Yamaguchi  Shoko Hina  Mari Hamahashi  Hugues Raimbourg  Romain Augier  Leslie Gadenne 《Island Arc》2012,21(4):231-234

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