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A fourth-order, fully two-way-coupled dual-domain Pacific Ocean Model (DUPOM) is developed to simulate the regional circulation in Asian Marginal Seas based on the whole North Pacific Ocean simulation framework. The model uses 1/4° and 1/8° horizontal resolutions for the eastern and western Pacific Ocean domains, respectively. The fully two-way-coupled approach shows seamless coupling behavior without any sponge layer. We validate the Kuroshio Current System and the regional circulation in the Asian Marginal Sea, including circulation patterns, volume transport variation and vertical current structure across several cross-sections. A single strong current core exists east of Taiwan and extends to the East China Sea. A cold dome near the northeast of Taiwan is a semi-permanent feature in the model results as observed. South of Japan (e.g. PCM5 line), the Kuroshio shows strong transport along the coast with a countercurrent offshore, reflecting a recirculation gyre. The transient of the three typical paths of the Kuroshio meander is also studied. Our results suggest that the path variation, particularly the Large Meander path, may be triggered by the baroclinic instability associated with westward propagating eddies.

The conveyor of the source water that feeds into the Taiwan Strait (TS), particularly from the south, is investigated using historical CTD (Conductivity-Temperature-Depth) data and a North Pacific Ocean and East Asian seas coupled model. The modeled currents and drifter trajectories suggest that the Kuroshio Branch Water (KBW) rarely flows directly into the TS from the Luzon Strait (LS) in winter; instead the massive westward movement of the Kuroshio conveys high salinity water to the southeastern TS through a loop-like route. In summer, the modeled flow fields suggest that the Kuroshio surface currents hardly intrude into the TS directly from the LS. Observations and model results show that the monsoon-driven northeastwardflowing currents in the northern South China Sea transport relatively low salinity water through the entire TS.

The impacts of global warming on the environment, economy and society are presently receiving much attention by the international community. However, the extent to which anthropogenic factors are the main cause of global warming is still being debated. There are obviously large stakes associated with the validity of any theory since that will indicate what actions need to be taken to protect the human race’s only home—Earth. Most studies of global warming have investigated the rates and quantities of carbon dioxide emitted into the atmosphere since the beginning of the industrial revolution. In this paper, we focus on the earth’s carbon budget and the associated energy transfer between various components of the climate system. This research invokes some new concepts: (i) certain biochemical processes which strongly interact with geophysical processes in climate system; (ii) a hypothesis that internal processes in the oceans rather than in the atmosphere are at the center of global warming; (iii) chemical energy stored in biochemical processes can significantly affect ocean dynamics and therefore the climate system. Based on those concepts, we propose a new hypothesis for global warming. We also propose a revolutionary strategy to deal with global climate change and provide domestic energy security at the same time. Recent ocean exploration indicates that huge deposits of oceanic methane hydrate deposits exist on the seafloor on continental margins. Methane hydrate transforms into water and methane gas when it dissociates. So, this potentially could provide the United States with energy security if the technology for mining in the 200-mile EEZ is developed and is economically viable. Furthermore, methane hydrate is a relatively environmentally benign, clean fuel. Such technology would help industry reduce carbon dioxide emissions to the atmosphere, and thus reduce global warming by harnessing the energy from the deep sea.

Low-pass-filtered velocities obtained from surface drifters and surface geostrophic velocities estimated from TOPEX/Poseidon altimeter data have recently revealed a clear and robust seasonal cycle in the surface eddy kinetic energy (EKE) in the California Current (CC) [Kelly et al., 1998; Strub and James, 2000]. The seasonal cycle begins in spring when a surface-intensified baroclinic equatorward jet develops next to the coast in response to strong upwelling favorable winds. This jet, and a developing eddy field, then moves offshore during summer and fall. The EKE maximum associated with the jet progresses only as far as 127°W, beyond which it decreases rapidly. This is a robust characteristic of the seasonal cycle that has been previously attributed only to an unspecified dissipation process. To investigate this aspect of the surface EKE, a multiyear simulation of the CC is carried out using the Dietrich/Center for Air-Sea Technology primitive equation regional ocean model [Dietrich, 1997]. The simulation accurately reproduces many aspects of the observed annual cycle, including the offshore propagation of the EKE at the surface. The model results indicate that the decrease of surface EKE west of 127°W in the simulation is not due to dissipation but rather is caused by the vertical redistribution of EKE to the deep ocean. This redistribution occurs through the transformation of kinetic energy from the vertical shear flow to the vertical mean flow. The transformation is a nonlinear process inherently associated with the life cycle of baroclinically unstable waves, and in the CC, it effectively energizes the deeper ocean at the expense of the upper ocean. The process is also known to be important in the atmosphere [Wiin-Nielsen, 1962]. Taken together, the recent California Current observations and the new model results strongly suggest that the CC regularly supplies EKE to the deep waters of the eastern North Pacific.

The surface waters of Doubtful Sound, a glacially carved fjord in south-western New Zealand, feature a quasi-permanent low-salinity-layer (LSL). The LSL is maintained year round by the extreme precipitation in the catchment (∼7 m yr −1 ) and discharge from a hydroelectric power station (∼450 m 3 s −1 ). The robust, stable LSL has been shown to play a major role in controlling intertidal and subtidal community structure. By contrast, little is known about the dynamics of the LSL itself. The work presented here elucidates the response of the LSL to perturbations in the wind stress and rainfall. Frequency-domain analysis of salinity data collected from an array of moored instruments revealed that the LSL responded to perturbations in both the winds and rainfall. However, the specific roles of the wind stress and rain could not be adequately resolved in these analyses. By contrast, simulations of the response of the LSL using a three-dimensional primitive equation model revealed that strong up-fjord directed wind events set up a storm surge at the head of the fjord. This surge significantly deepens the LSL at the head of the fjord and retards or reverses estuarine circulation. The subsequent relaxation of the surge after the abatement of the wind stress resulted in a redistribution of buoyancy throughout the fjord over a two-day period. It is shown that the development and relaxation of the storm surge is a major process controlling the maintenance of the near-surface stratification.

The development and verification of a new version of the DieCAST ocean circulation model to be referred to as CANDIE (Canadian Diecast) are considered. Both CANDIE and DieCAST have many features in common with the well-known Modular Ocean Model (MOM) of the Geophysical Fluid Dynamics Laboratory. Of particular relevance to the present study are the rigid-lid approximation and the use of standard Cartesian coordinates. The DieCAST formulation in terms of the surface pressure, rather than the volume transport streamfunction, is also used in CANDIE to reduce numerical sensitivity to ocean depth variations. The major difference between MOM and DieCAST is the use of a mixed C and A grid formulation in DieCAST rather than the B grid formulation used in MOM. CANDIE differs from DieCAST in the use of a standard C grid formulation and a reduction in the magnitude of the time truncation error associated with the implicit treatment of the Coriolis force. The implementation of the rigid-lid approximation is r...

The Gulf of Mexico (GOM) circulation is simulated using the DieCAST ocean model, with a horizontal resolution of 1/12° and 20 vertical layers. The results compare well with observations of both large and small scale features, including Loop Current frontal occlusions associated with frontal eddies. The simulation is carried out without any data assimilation. The frontal eddies tend to be spaced at about 90° intervals around the Loop Current, leading to a Loop Current head shaped like a square with rounded corners. The pattern rotates as the eddies circle the Loop, and frontal eddies elongate as they squeeze through the Florida Strait. Major warm core eddies separate regularly from the Loop Current and propagate to the western GOM. Old warm core eddies in the western Gulf dissipate through bottom drag effects, which also generate cyclonic parasitic eddies. Newly arrived warm core eddies merge with old ones in the western GOM. Recently separated elongated Loop Current eddies can rotate and reattach temporarily to the Loop Current. The barotropic flow component develops eddies between the main separated warm core eddy and the Loop Current due to eastward dispersion, as the main eddy itself propagates westward into the Gulf.

Two and three-dimensional oceanic flows around small islands patterned after Barbados, W.I. (13° 10′ N latitude: 59° 30′ W longitude) were modeled numerically to investigate island wake effects. The two-dimensional simulations closely agreed with laboratory flows, for both attached and shedding wake regimes. As expected, results for a flat bottom confirmed that the Coriolis terms strongly affect pressure but not the flow. For idealized, yet typical incident flow speeds, water column stratification, island topography and appropriate Coriolis terms, three-dimensional simulations readily produced elongated wake patterns, dominated by surface intensified von Karman-like vortices. Effects of grid resolution, viscosity, bathymetry, and Coriolis forces on wake characteristics were studied. For islands with typical bottom slopes, realistically small horizontal eddy diffusivity has a minor effect compared to bottom drag in generating vorticity. Near-shore bathymetry (viz., the absence or presence of a con...

In application to the Gulf of Mexico (GOM), a new DieCAST ocean model, which uses a modified Arakawa ‘a’ grid, and the SOMS model, which uses an Arakawa ‘c’ grid, give remarkably similar results. The new model avoids ‘null space’ problems of the standard ‘a’ grid approach by first using fourth-order interpolations to a ‘c’ grid advection velocity, then applying incompressibility to the result. Accuracy is further improved by using fourth-order pressure gradient approximations at ‘a’ grid locations. Incompressibility with general geometry is satisfied efficiently by a fast-converging iteration with a regular gteometry elliptic solver. Results are compared with satellite-measured r.m.s. sea surface elevation anomaly and detailed front structures, climatological mean thermocline and empirical orthogonal functions and other observations.

We use a 2-dimensional non-hydrostatic model on the vertical plane to examine the nature of convective adjustment. In the first part of the study, we investigate the mixing of an initial unstably stratified 2-layer fluid with molecular viscosities. The linear growth rates compare well to those obtained using an analytic model. The stratification of the convectively adjusted state is sensitive to the Prandtl number (Pr, the ratio of the eddy viscosity to thermal diffusivity). This is important as the instantaneous convective adjustment used in coarse resolution ocean circulation models corresponds to Pr→0, while the case of immiscible fluids corresponds to the limit of large Pr. Mixing in the ocean as well as in our numerical model are both characterized by a finite value of Pr. In the second part of the study, we scale up to ocean scales with a more realistic surface forcing and turbulent viscosities. The implications of our results for instantaneous convective adjustment are discussed.

New, fourth‐order “c” grid Coriolis term treatments are compared with widely used second‐order treatments. Their improved accuracy is demonstrated by a grid convergence study for a relevant linear problem. Such an accuracy improvement is relatively easy and costs little for low Rossby number flows compared with high Rossby number flows, because one must consider only the Coriolis and pressure gradient terms in low Rossby number flows. The “c” grid is favourable for the latter, but the Coriolis terms benefit greatly by the higher order treatments analysed herein.

Five numerical schemes are compared using convergence studies in the framework of the hydrostatic Sandia Ocean Modeling System (SOMS). Three resolutions are used, 40, 20 and 10 km, with respectively three, seven and 15 layers and time steps of 60, 30 and 15 min, so 15 convergence calculations are performed. The same geophysical prototype problem (exhibiting baroclinic instability in a statically stable environment) is used for all calculations. All five schemes are second-order-accurate in space, but those using four-point interpolations for the Coriolis and pressure gradient terms are shown to produce much more accurate results, with relatively little extra computation, than schemes using two-point interpolations. Convergence is also indicated with decreasing horizontal diffusivities of 107, 106, and 105 cm2s−1. Using 107 cm2s−1 diffusivities causes substantial damping of the dominant instabilities during the 30-day integrations performed, but using 106 cm2 s−1 results in little damping and yields results very close to those using 105 cm2 s−1. A barotropic (vertically averaged flow) cyclonic northern basin gyre is explained as a weakly forced circulation. Its equilibrium amplitude is determined by a balance between dissipation effects due to horizontal mixing and diffusion, and weak second-order driving associated with thermodynamic forcing and vorticity dissipation at the basin bottom. It is thus quite sensitive to model dissipation but can be well described by SOMS owing to SOMS' low numerical dissipation.

The aspiration of spherical particles which are suspended without sedimentation in an ideal fluid that flows past a thin-walled sampler is investigated. A recent experimental study showed that secondary aspiration caused by particles bouncing off the walls of the nozzle and subsequently entering the nozzle inlet is of importance in determining the aspiration efficiency of samplers in many situations. Therefore the extent of oversampling caused by particle rebound is investigated using a numerical method. Three situations are considered, namely, when the particles (1) adhere to the sampler surface on impact, (2) bounce off the surface and all those that hit within a certain area, known as the stagnation area, are eventually sampled, and (3) bounce off the surface with no loss of energy. Results for the three cases are compared and they are found to display the same trends as found in the experimental investigations.

Guidelines are presented for efficient design and application of opposed swirl internal mix nozzles. Associated fluid dynamic mechanisms are briefly discussed.

Mathematical computer models are currently being used with relevant observations to assess the transport and dispersion of soluble and suspendable materials originating from bottom sources in the deep ocean. For realistic results, ocean models must treat complex phenomena sources on a range of scales, including basic gyre-scale flow, the mesoscale eddy field, phenomena such as boundary-layer separation associated with bottom topography, and turbulent mixing processes in the bottom boundary-layer. The Sandia ocean modelling system (SOMS) is a system of primitive equation numerical models.

A base state formalism is used to maximize the dominance of adiabatic compression wave propagation terms solved directly (implicitly at )the advanced time level in a filtered trapezoidal time integration scheme designed for subsonic compressible gas flows. This approach is enhanced by using efficient direct SEVP solvers for the resulting variable coefficient elliptic system. To facilitate implicit treatment of the dominant adiabatic compression wave terms, a convenient form of the energy equation is used. Extensions to two-phase flow and general equations of state are described. Applications to jet penetration and to a coal gasification reactor are described.

Physical phenomena fundamental to rotating, baroclinically driven flows are studied with reference to results of numerical simulation of rotating annulus flows, using a modified Galerkin Model. Both local and global effects of sources, sinks, and transports of heat and momentum are discussed. A convenient ‘energy exchange” diagram reveals detailed information that is used to analyze nonlinear equilibration and amplitude vacillation of quasi-geostrophic baroclinic eddies. Transient inertial oscillations, sidewall boundary layers, and internal boundary layers are also discussed. A detailed study of symmetric flows is made, eleven of which are tested numerically for stability with respect to three-dimensional disturbances of a given zonal wave number. Two of the four unstable cases are integrated to a numerical steady state with finite-amplitude, quasi-geostrophic baroclinic waves. With the ‘rigid-lid’ geometry assumed, the average zonal velocity is zero, resulting in zero phase velocity of the waves. The structure of the thermal wave is nearly coherent in the vertical. These numerical results are consistent with laboratory observations. The eddy flow is quasi-geostrophic except in horizontal boundary layers, where the flow is driven toward low pressure. A small cross-isotherm advection is sufficient to maintain the temperature wave against diffusion and vertical advection. The eddy flow adjusts spontaneously toward the form of the fastest growing or slowest decaying disturbance representable by the truncated space resolution. The eddy flow feeds energy into the mean zonal flow in ‘barotropic-type’ interactions reflected mainly by the familiar ‘tilted trough’. During equilibration, the eddy flow alters the mean zonal flow in such a way that eddy energy sources are reduced relative to energy sinks. However, this adjustment is small compared to the change of total flow, which reflects a relatively large change of eddy amplitude. This suggests that small errors in the mean zonal flow representation can lead to relatively large errors in total flow representation. In most flows studied the kinetic energy dissipation is concentrated in thin boundary layers. In spite of this thinness, the basically laminar character of these dissipative boundary layers allows accurate and economical numerical simulation through the use of characteristic functions, which is a natural refinernent of the basic Galerkin method used. (In this prototype study, only “moderately characteristic’ functions are used, thus sacrificing numerical economy while simplifying the programming.) Similarly, the generation of potential energy, which is transformed into the kinetic energy of the flow, is accurately simulated. In most cases studied, this generation is also concentrated in thin boundary layers where thermal energy is extracted from cold fluid and added to warm fluid.