Development of the current induced by the topographic heat accumulation (I)     

Yukio Oonishi 《Journal of Oceanography》1975,31(6):243-254

Some numerical experiments were made to examine the possibility of large anticlockwise circulation at Lake Biwa in summer caused by horizontally uniform heat flux across the lake surface. Flow is induced by the “topographic heat accumulation effect” due to the non-uniform water depth. To evaluate this flow, an axisymmetric model basin is used. Dependence of the magnitude of velocity on the horizontal and vertical Ekman numbers is also investigated. If the heating continues as long as the vertical diffusion time, fairly large velocity is created indicating a possibility that this is the origin of the lake current.  相似文献   

Testing of a towed CTD     

Yukio Fujinawa  Yoshinobu Tsuji  Isao Watabe  Ken Sasaki  Masao Nomoto  Toshiaki Hara  Yoshito Tsuji 《Journal of Oceanography》1980,36(5):253-258

The results of laboratory and field experiments on a CTD measuring unit attached to a controllable towed body is described. It was verified that the three-dimensional distribution of salinity and temperature could be observed with sufficient accuracy (to 0.03 in salinity and to 0.01°C in temperature if proper correction is adopted) while cruising at up to 4 knots. A double integrated A/D converter is used to compensate for effects of extraneous environmental changes.  相似文献   

Algal Growth Potential and the limiting nutrient in Mikawa Bay     

Masao Kondo  Tsutomu Sakai  Hajime Yamamoto  Yukio Arakawa 《Journal of Oceanography》1984,40(5):391-396

The Algal Growth Potential (AGP) of water samples collected off Gamagori in Mikawa Bay was measured from May 1978 through February 1979, and the limiting nutrient was determined using regression analysis and enrichment bioassays. The surface and bottom water samples had AGP that produced increments of chemical oxygen demand (COD) of 2.1 mg l^–1 and 3.1 mg l^–1, respectively, on average. These values ofCOD correspond to 46% and 97% of the average COD values of the raw water samples at the surface and bottom, respectively. Seasonal changes of AGP showed a close correlation with those of dissolved inorganic nitrogen (DIN) concentration. Enrichment bioassays showed that DIN was the most deficient nutrient. The DIN:phosphate-phosphorus (PO₄ ^3–-P) ratios and DIN: dissolved phosphorus (DP) ratios in the water samples were below the cellular N:P ratios of the natural algal populations. These results suggest that AGP was mainly limited by DIN concentration.  相似文献   

A numerical study on the tidal residual flow     

Yukio Oonishi 《Journal of Oceanography》1978,34(4):140-159

Characteristics of the tidal residual flow, the steady current induced in the tidal current system, are studied by a numerical method. The model basin has the same topography as that studied byYanagi (1976) and byOonishi (1977) where only the horizontal motion of the residual flow is concerned. In this study, the effect of the vertical motion is investigated as it is associated with the tidal residual flow. To this end, the bottom friction omitted in the previous study (Oonishi, 1977) is included and a two-leveled model is adopted.The first two experiments exclude the earth's rotation and the buoyancy effect on the flow. The results are as follows. The horizontal flow pattern is essentially the same as that obtained in the previous Oonishi study. The bottom friction results in the reduction of the velocity of the residual flow especially in the bottom level. An important result is that vertical velocity is as strong as the horizontal velocity multiplied by the scale ratio and that it remains even in the time-average. Upwelling appears at the center of the residual circulation. This upwelling explains Yanagi's observation in the hydraulic model that the sediment is swept by the flow and accumulates horizontally in the area at the bottom below the center of the residual circulation. The distribution of a tracer, which is simultaneously calculated in these cases, indicates the important role of vertical motion in the material dispersion in the model.The last experiment includes the earth's rotation and the buoyancy effect presuming a more actual sea. It shows another effect of the vertical motion. The Coriolis term, which operates only under the condition that a horizontal divergence of the flow is present, skews the horizontal residual flow pattern.  相似文献   

A numerical study on the tidal residual flow     

Yukio Oonishi 《Journal of Oceanography》1977,33(4):207-218

A fundamental mechanism of generation of the tidal residual flow, the steady or quasi-steady flow induced in the tidal current system, is studied by numerical methods. The model basin is a very simple one, a rectangular basin of 5m×10m of constant depth and with a cape of 4 m length jutting out at a right angle from the center of the longer side wall. This basin has the same topography as that studied byYanagi (1976) by means of the hydraulic model experiments.The steady, circular, horizontal current is found to be induced through the following processes. Horizontal friction at the coast makes the vorticity of vertical component in the oscillating flow. Self-interaction of this flow causes the vorticity transfer to the steady flow in frequency domain. This vorticity transfer is confined in the narrow coastal boundary layer. The steady flow advects the transferred vorticity and makes itself develop fully wide over the bay. In other words, there are two kinds of cascade-up, one with regard to time scale and the other with regard to horizontal space scale.When the tidal range, the tidal period and the horizontal eddy viscosity change under the condition that the model geometry is fixed, the nondimensional parameter which controlls the steady flow is found to be the Reynolds number of the oscillating flow.  相似文献   

The uranium content and the activity ratio234U/238U in marine organisms and sea water in the western North Pacific     

Yasuo Miyake  Yukio Sugimura  Masaru Mayeda 《Journal of Oceanography》1970,26(3):123-129

The uranium content and activity ratio A²³⁴U/A²³⁸U were determined in open ocean water, marine plankton, marine algae and sea water in the environment in which plankton and algae live. The average uranium content of 3.34±0.28×10⁻⁶ g/l and the average activity ratio of 1.13±0.04 were obtained in open ocean water. The uranium contents in plankton and algae were respectively from 1.7 to 7.8×10⁻⁷ g/g and 0.4 to 23.5×10⁻⁷ g/g on dry basis with the respective concentration factors of 48 to 260 and 10 to 733. The activity ratio in plankton and algae ranged from 1.07 to 1.18 which coincided well with those in the environmental sea water.  相似文献   

Chemical forms of minor metallic elements in the ocean     

Yukio Sugimura  Yoshimi Suzuki  Yasuo Miyake 《Journal of Oceanography》1978,34(3):93-96

In order to clarify the chemical forms of minor metallic elements occurring in the ocean, a new method of separation of organic compounds of metals in sea water by using XAD-2 resin was contrived. By applying the new method of determination, it is found that, (1) More than 80 % of V, Fe, Cd and Cu dissolved in sea water are present in organic forms regardless of the depth; (2) A most part of Co and Pb are present in organic forms near the surface, but they change into inorganic forms in the deep layer up to 50 to 60%; (3) Of the total amounts of dissolved Al, Ni, Zn, Ag, Mo, and U, less than 30 % are present in organic forms in sea water anywhere in the ocean; (4) Up to 45% of Se is in organic forms.  相似文献   

The coriolis effect against frontogenesis in steady buoyancy-driven circulation     

Akira Harashima  Yukio Oonishi 《Journal of Oceanography》1981,37(1):49-59

The Coriolis effect on frontogenesis in the transitional region between the inner bay and the outer ocean is studied by running several three-dimensional numerical experiments. The aim is to clarify what external parameters, including the transverse scale of the basin, control the phenomena. The characteristics of the front in each case are described by defining three diagnostic quantities, namely, the sharpness of the front, the intrusion of the front, and the buoyancy difference between the minimum buoyancy region and the surrounding part, as the existence of the minimum buoyancy region is closely related to frontogenesis. The three quantities are shown to depend on two nondimensional numbers,R _of (=f ⁻¹ L ^−2/3 F _b ^1/3 : defined as flux Rossby number) andR _ef (=ν _v ⁻¹ L ^−2/3 F _b ^1-3 H ²: defined as flux Reynolds number).  相似文献   

Water exchange between adjacent vortices under an additional oscillatory flow     

Yukio Oonishi  Hideaki Kunishi 《Journal of Oceanography》1979,35(3-4):136-140

It is shown that the coupling effect of the steady vortices and the Eulerian oscillatory flow yields the 8-shaped Lagrangean motion through which adjacent vortices intercommunicates, inducing water exchange between them. The water exchange coefficient is fairly large. This coupling effect is considered to play an important role in the water exchange across the narrow strait which is accompanied with a strong tidal current and a pair of tidal residual circulations.  相似文献   

Study on the currents in Lake Biwa (II)     

Yukio Oonishi  Norihisa Imasato 《Journal of Oceanography》1975,31(2):53-60

Some numerical experiments are made using a linear barotropic model of Lake Biwa to investigate the current induced by the spatially uniform wind stress. Concerning the phenomena whose time scale is longer than the inertial period, we integrate the non-divergent vorticity equation.It is found that the topographic curl of the wind stress which comes from the bottom topography and the wind stress induces circular currents and that the current, generated by the wind, attenuates gradually accompanying the topographic Rossby wave whose period is about 9 half-pendulum days in Lake Biwa. This mechanism of the barotropic response of the lake water to the wind will explain well the unsteady lake current in Lake Biwa in winter.  相似文献