OS51A-01
Quasi Two-Dimensional Turbulent Flow Over Discontinuous Topography
Decaying turbulent flows with topography are studied by means of laboratory experiments in a rotating tank and by numerical simulations based on a quasi-two-dimensional model. The basic configuration is a step-like topography dividing the flow domain in deep and shallow regions. The main objectives are: to prove that different domain geometries influence the long-term flow evolution; to show the generation of a final flow configuration; and to examine the physical mechanisms behind the main interactions of simple structures with the topography, like dipoles, in order to explain the final flow distribution.
OS51A-02
Numerical Simulation of Storm surges/Wave using KMA Operational Ocean Model
The Korea Meteorological Administration (KMA) has operated numerical ocean wave prediction system since 1992. Prior June 1999, the 1st generation wave model (DSA-5) was operated twice in daily over the Northeast Asia region. With introduction of NEC SX5 supercomputer in 1999, the 3rd generation wave model (WAM) was implemented with two wave prediction systems ¡V the ReWAM (Regional WAve Model) and the GoWAM (Global WAve Model). At present, KMA (Korea Meteorological Administration) has operated the wave model and storm surge model based on CRAY X1E system. The study shows development and verification of operational ocean model and future plan of KMA. The operational storm surge model (STOM : Storm surge/Tide Operational Model) area covers 115¢X-150¢XE, 20¢X-52¢XN based on POM (Princeton Ocean Model) (Blumberg and Mellor, 1987) with 1/12¢X horizontal resolutions including the Yellow Sea, East China Sea and the East Sea, marginal seas around Korea. From July, 2006 the STOM have been applied to formal forecasting model in KMA. Sea surface wind and pressure from the Regional Data Assimilation and Prediction System (RDAPS) is used for forcing input of storm surge model. In this model, the level of storm surge calculated by the difference between tide level and sea level change caused by meteorological effects. The newly developed operational wave model is WAVEWATCH III which is a third generation wave model developed by Tolman (1989). The Regional WAVEWATCH III (RWW3) covers the northwestern Pacific Ocean from 115„aE to 150„aE and from 20„aN to 50„aN similar to STOM. The horizontal grid intervals are 1/12„a in both latitudinal and longitudinal directions. The RWW3 is integrated from a state of rest and forced by the RDAPS wind stress produced by KMA. From 2007, the RWW3 will be applied to formal forecasting model in KMA. The Coastal WAVEWATCH III (CWW3) covers 6 coastal areas around Korea peninsular. The horizontal grid intervals are 1/120„a for each area. Under the renewal process of power computing packs at KMA on the year 2005, the CRAY X1E system (14.5 Teraflops) replaced NEC SX5 (224 Gigaflops). Establishing of newly devised ocean prediction system is underway in conjunction with high computing environment. The main focus of new wave system lies in accommodating coastal wave/surge processes. The west and the south coastal area of Korean peninsular is one of the challenging places in ocean modeling for reasonable prediction of nearshore wave conditions and tides.
OS51A-03
Nonlinear Internal Waves Over a Sloping, Dissipative Bottom
A new model for propagation of nonlinear internal waves in coastal areas in considered. The model takes account for an inhomogeneity such as a sloping bottom and for the losses such as the bottom friction in shallow zones. The model is based on the Hamiltonian approach resulting in derivation of an evolution equation applicable for strongly nonlinear waves, for which both the mass and energy are conserved (unlike the previous evolution models for which only either of them were conserved). Processes of formation and destruction of solitons and soliton groups (solibores) are considered. Whenever possible, comparisons with observational data are presented.
OS51A-04
Wakes of Maneuvering Bodies in Stratified Fluids
We present the results of experimental/theoretical studies on large momentum eddies generated in late wakes of unsteady moving self-propelled bodies in stratified fluids. The experiments were conducted with scaled submarine model at high Reynolds numbers (50,000), corresponding to the fully turbulent flow regime. Dye visualization and PIV were used for flow diagnostics. When a self-propelled body makes a maneuver, e.g. accelerates, it imparts net momentum on the surrounding fluid. We show that in a stratified fluid this leads to impulsive momentum wakes with large, long-lived coherent vortices in the late flows, which may be used as a signature for identification of submarine wakes in oceanic thermocline. First, we consider dynamics and properties of such wakes in a linearly stratified fluid and present a model that permits to predict the main flow characteristics. Second, we consider wakes in a two layer stratified fluid (analog of the upper ocean) and show that such wakes may penetrate to the water surface; we present a model for this phenomenon and propose criteria for the penetration of wake signatures to the water surface in terms of main governing parameters (signature contrast versus confinement number). Finally, we consider the evolution of such momentum wake eddies in the field of decaying background turbulence, which mimics the oceanic thermocline, and show that for the flow configuration studied the contrast number remains sufficiently large and detectable wake imprints survive for a long period of time. Some pertinent estimates for submarines cruising in the upper ocean are also given. For more details see [1-3]. This study was supported by grant from the Office of Naval Research. 1. Voropayev S.I., Fernando H.J.S., Smirnov S.A. & Morrison R.J. 2006. On surface signatures generated by submersed momentum sources. Phys. Fluids, under revision. 2. Voropayev S.I., Fernando H.J.S. & Morrison R.J. 2006. Dipolar eddies in a stratified turbulent flow. J. Fluid Mech., submitted. 3. Voropayev S.I., Smirnov S.A. & Fernando H.J.S. 2007. Late-wake vortices of maneuvering bodies in stratified fluids. J. Fluid Mech., submitted.
OS51A-05
Connections between Equatorial Pacific and Peruvian current system in a high-resolution numerical model
Historically patterns of the ocean currents in the eastern south tropical Pacific have been deduced from eulerian current measurements or geostrophic flow estimates that lack spatial/temporal resolution to provide a reliable description of true Lagrangian pathways. As a result, limited information exists regarding the connections between equatorial currents and the Peruvian current system. Making use of the Lagrangian submodel developed for ROMS model outputs, we investigate these connections under climatological conditions. Our results show that the model reproduces the two main branches of the eastward zonal flow that are of interest to us. The first branch is the Equatorial Undercurrent (EUC) located between 1°N and 1°S. The second one is the South Extension of EUC (SEEUC) located between 3 - 4°S. Farther south, another current, called the Southern Subsurface Countercurrent (SSSCC), is also identified and located between 7 and 8°S above 250 m depth. Most importantly, the Lagrangian trajectories suggest that the subsurface poleward currents off Peru (Peru-Chile Undercurrent) are fed not only by the SEEUC but also by the SSSCC, and to a weaker extent by the EUC. With the help of another type of Lagrangian experiments, origins of the upwelled water off the Peruvian shelf are shown to be of direct equatorial sources and of off-shore subsurface recirculation.
OS51A-06
Inner Shelf Circulation Patterns Under Downwelling and Stratified Conditions off a Curved Coastline
Recent observations in Long Bay, SC (USA), a typical shelf environment with a curved coastline bounded by capes, showed the existence of a countercurrent near the shore during downwelling favorable wind. Motivated by this, a 3D numerical study (using ROMS) was carried out to investigate downwelling circulation patterns that develop on a stratified shelf with a curved coastline. Numerous numerical experiments were carried out using an ideal domain for stationary or variable wind stress and various bottom friction settings. The results show that for all experiments the curved coastline leads to the generation of both a velocity and pycnocline disturbance at the upstream cape, which propagates in the downwind direction. This transient disturbance is more pronounced under non-stationary forcing and is best developed after the wind stress peaks. The propagation path differs depending on the relative strength of inertia and bottom friction in the vicinity of the capes. When inertia dominates, the disturbance detaches from the cape and travels downwind along the isobaths. In this case, a strong countercurrent develops near the shore. When friction is more important than inertia, the disturbance propagates at a lower speed and is located close to the shore (i.e., coastline-arrested disturbance). This results to a significant alongshore temperature gradient and the formation of an almost shore- perpendicular thermal front that moves with the disturbance. The numerical results appear to agree with the observations in Long Bay and with satellite imagery and emphasize the role that the coastline morphology can play a role in enhancing cross-shelf transport and exchange.
OS51A-07
Numerical Study of the Circulation and Sediment Transport in the Region of the Southeast American Shelf Under the Influence of the Plata River and the Patos Lagoon
In the past few years, there has been an increasing interest in the dynamics of the plume formed by waters of the Plata River and the Patos-Mirim Lagoon System. This is due to the impacts of these low-salinity waters on physical, chemical and biological processes in this region. In this work will be present modeling results of sediment transport along the continental shelf between Mar Del Plata (~ 40°S) and Cabo Frio (~ 22°S), in which we explore the impacts of the discharge on the sediment concentration along the shelf. The model used is the ECOMSED (Estuarine and Coastal Ocean Model and SEDiment transport model), in an implementation that presents variable horizontal resolution, with 40 km in the far region and 7 km resolution near the mouth of the Plata River. The vertical resolution has 21 sigma levels. In the preliminary results, we were able to reproduce a standing region that was referred by Framiñan et al. (1996) as the Maximum Turbidity Front. In general, however, part of the sediments are transported out of the estuary onto the adjacent continental shelf. Due the influence of southwest winds, the plume flows more to northeast around the coast up to low latitudes (~ 20°S). In our study we expect to correlate the impact of this northward extension of the plume on the sediment concentration on the shelf.
OS51A-08
Vorticity Generation and Evolution in the Shallow-Water Island Wake
To investigate the mechanism of vorticity generation and evolution in the wake of an island with shelf slope, Regional Oceanic Model System (ROMS) is applied. An idealized island shape with shelf slope is configured with a stratified and rotating flow passing the island. Numerical results show that the mechanism of eddy generation in the wake of the island with the shelf slope is different from our previous study of deep-water island wake: uneven-distributed bottom viscous stress becomes import in the eddy generation, associated with vortex stretching and baroclinic vertical tilting. To isolate the bottom stress from baroclinic vertical tilting, slippery bottom is used in a paralleling numerical experiment. More detailed analysis of the numerical experiments will be presented in the presentation.