A numerical study on the tidal residual flow

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.     

Formation of water masses and fronts due to density-induced current system

Several numerical experiments were carried out on the formation of water masses and their fronts such as observed in the Kii Channel in winter. Such water masses and fronts may caused by density-induced current system. The phenomenon is assumed to take place in the vertical two-dimensional plane not involving the effect of the earth's rotation. The linear momentum equation and the diffusion-advection equations of salinity and temperature are integrated with respect to time under a vertically hydrostatic condition. The result is that two rolls which correspond to the onshore water mass and the offshore water mass are formed with an accompanying front between them. The apparent diffusion coefficient reaches a relatively great amount inside the water masses and drops down to the eddy diffusivity level at the front. The dependence of the synoptic distributions of the temperature and salinity on several parameters is also examined. Finally another experiment is carried out involving the effect of the earth's rotation, which results in a rather different distribution pattern from that of the non-rotating model.     

A numerical study on the tidal residual flow

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.     

Study on the currents in Lake Biwa (II)

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.     

Fifteen years progress of the TRITON array in the Western Pacific and Eastern Indian Oceans

The Triangle Trans‐Ocean Buoy Network (TRITON) project by the Japan Agency for Marine-Earth Science and Technology began with deployment in the western tropical Pacific Ocean in 1998 and has shifted to steady, long-term observations since 1999. After on-site inter-comparison with the Autonomous Temperature Line Acquisition System mooring system of the Tropical Atmosphere and Ocean (TAO) array by the National Oceanic and Atmospheric Administration, the TRITON array became the international TAO/TRITON array in 2000 as a key component of the Global Ocean and Climate Observing Systems. The TAO/TRITON array took over from the TAO array, which was developed during the Tropical Ocean and Global Atmosphere program (1985–1994), and replaced the western part of TAO with new additional real-time measurements of salinity and ocean currents. In 2001, two TRITON moorings were deployed in the eastern Indian Ocean for capturing the eastern pole of the Indian Ocean Dipole. From this initiative, the Indian Ocean Observing System (IndOOS) was designed, and the Indian Ocean mooring array (Research Moored Array for Africa–Asian–Australian Monsoon Analysis and Prediction) was developed as a key component of IndOOS. In this paper, 15 years of progress in the TRITON project in the western Pacific and eastern Indian Oceans is reviewed with regards to scientific outcomes, technological development, and collaborations with international and domestic partners. Future directions for sustainable observation in the Pacific and Indian Oceans are also discussed.     

What controls equatorial Atlantic winds in boreal spring?

The factors controlling equatorial Atlantic winds in boreal spring are examined using both observations and general circulation model (GCM) simulations from the coupled model intercomparison phase 5. The results show that the prevailing surface easterlies flow against the attendant pressure gradient and must therefore be maintained by other terms in the momentum budget. An important contribution comes from meridional advection of zonal momentum but the dominant contribution is the vertical transport of zonal momentum from the free troposphere to the surface. This implies that surface winds are strongly influenced by conditions in the free troposphere, chiefly pressure gradients and, to a lesser extent, meridional advection. Both factors are linked to the patterns of deep convection. Applying these findings to GCM errors indicates, that, consistent with the results of previous studies, the persistent westerly surface wind bias found in most GCMs is due mostly to precipitation errors, in particular excessive precipitation south of the equator over the ocean and deficient precipitation over equatorial South America. Free tropospheric influences also dominate the interannual variability of surface winds in boreal spring. GCM experiments with prescribed climatological sea-surface temperatures (SSTs) indicate that the free tropospheric influences are mostly associated with internal atmospheric variability. Since the surface wind anomalies in boreal spring are crucial to the development of warm SST events (Atlantic Niños), the results imply that interannual variability in the region may rely far less on coupled air–sea feedbacks than is the case in the tropical Pacific.     

Testing of a towed CTD

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.     

A new formula for evaluating the truncation error coefficient

In this paper, a new formula for evaluating the truncation coefficientQ _n is derived from recurrence relations of Legendre polynomials. The present formula has been conveniently processed by an electronic computer, providing the value ofQ _n up to a degreen=49 which are exactly equal to those of Paul (1973).     

Geology of the Gorny Altai subduction–accretion complex, southern Siberia: Tectonic evolution of an Ediacaran–Cambrian intra-oceanic arc-trench system

The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic–Early Paleozoic age, such as an accretionary complex (AC), high-P/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient subduction–accretion processes. This study investigated the detailed geology of the Upper Neoproterozoic to Lower Paleozoic rocks in a traverse between Gorno-Altaisk city and Lake Teletskoy in the northern part of the region, and in the Kurai to Chagan-Uzun area in the southern part. The tectonic units of the studied areas consist of (1) the Ediacaran (=Vendian)–Early Cambrian AC, (2) ca. 630 Ma HP complex, (3) the Ediacaran–Early Cambrian OP complex, (4) the Cryogenian–Cambrian island arc complex, and (5) the Middle Paleozoic fore-arc sedimentary rocks. The AC consists mostly of paleo-atoll limestone and underlying oceanic island basalt with minor amount of chert and serpentinite. The basaltic lavas show petrochemistry similar to modern oceanic plateau basalt. The 630 Ma HP complex records a maximum peak metamorphism at 660 °C and 2.0 GPa that corresponds to 60 km-deep burial in a subduction zone, and exhumation at ca. 570 Ma. The Cryogenian island arc complex includes boninitic rocks that suggest an incipient stage of arc development. The Upper Neoproterozoic–Lower Paleozoic complexes in the Gorno-Altaisk city to Lake Teletskoy and the Kurai to Chagan-Uzun areas are totally involved in a subhorizontal piled-nappe structure, and overprinted by Late Paleozoic strike-slip faulting. The HP complex occurs as a nappe tectonically sandwiched between the non- to weakly metamorphosed AC and the OP complex. These lithologic assemblages and geologic structure newly documented in the Gorny Altai region are essentially similar to those of the circum-Pacific (Miyashiro-type) orogenic belts, such as the Japan Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient subduction zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran–Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-trench setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.     

A method for analyzing the expansion and shrinkage of point pattern

This article proposes a new method for analyzing the spatial expansion and shrinkage of point patterns. Spatial expansions of epidemic diseases and market areas are represented as the expansions of point patterns when disease cases and store customers are represented as points. The spatial expansion and shrinkage have been studied in many scientific fields. Existing analytical methods, however, are not sufficient for treating complicated spatiotemporal patterns. To answer this demand, this article develops a new method for analyzing the expansion and shrinkage of points. Three vector measures evaluate the degree and direction of expansion and shrinkage as functions of location and time. They are visualized as vector maps, which are valid for capturing the global spatiotemporal pattern as well as for discussing the local variation. Summary measures of these vectors allow us to grasp the overall spatiotemporal pattern efficiently. To test the validity of the proposed method, this article applies it to the analysis of visitors to Shinjuku and Ginza in Tokyo. The proposed measures permitted us to evaluate the spatiotemporal pattern of the visitors in detail and to consider its underlying structure from various perspectives, which indicated the soundness of the technique.