https://www7320.nrlssc.navy.mil/pubs/2006/barron_kara_06.pdf

Formulation, implementation and examination of vertical coordinate choices in the Global Navy Coastal Ocean Model (NCOM)

[1] A numerical simulation of the Gulf of Mexico (GoM) using the Navy Coastal Ocean Model (NCOM) is used to identify the pathways by which fresh water discharged by major rivers in the northern Gulf is exported away from the region. The NCOM, a new primitive equation ocean model with a hybrid sigma/geopotential level vertical coordinate, is described along with its application to the GoM region. Trajectories from surface drifters are analyzed to show evidence of the seasonally shifting alongshore and cross-shelf transport in the region. The model results are used to determine the preferred locations and times of year for cross-shelf and along-shelf export of low-salinity water from the northern GoM. The annual cycle of local wind stress plays an important role in shifting the export pathway of the fresh water discharged from the major rivers (primarily the Mississippi River) toward the east in the spring/summer, where it can be transported offshore by the currents associated with deep ocean mesoscale eddies, and toward the west in the fall/winter, where it is transported southward along the Mexican coastline as a coastally trapped current.

/pdf/export-pathways-for-river-discharged-fresh-water-in-the-4c4yssckul.pdf

Export pathways for river discharged fresh water in the northern Gulf of Mexico

[1] A coupled Adriatic Sea General Circulation and sediment transport model was used to study the dynamics of coarse and fine sediment transport and resuspension in the Northern Adriatic Sea. The sediment sizes of coarse (>50 μm) and fine (<50 μm) materials were sorted by their settling velocities. The bottom boundary layer (BBL) was discretized by a vertical sigma coordinate system with high resolution, and the wave-current interaction mechanism was considered. The sediment distributions and fluxes under various forcing conditions such as the Po River plume, the Bora and Scirocco wind stress and the surface waves were studied by process oriented numerical simulations. The conclusions are that maximum northward sediment transport occurs under the forcing by the Po River plume with the Scirocco wave resuspension. The largest southward sediment transport was due to the combined effect of the Po River plume and the Bora wind-forcing under the Bora wave conditions. A realistic forcing numerical experiment was also conducted for November 1994 when the full range of forcing functions were experienced by the region. This study shows that wave-driven sediment resuspension is an important resuspension mechanism in the shallow coastal areas of the Northern Adriatic Sea, and contributes significantly to the complexity of the sediment distribution and flux features in the region.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JC001303

Modeling the dynamics of sediment transport and resuspension in the northern Adriatic Sea

Using an eddy-resolving ocean circulation model endowed with active thermodynamics and a turbulence closure parameterization, a hierarchy of numerical experiments is carried out to investigate the relative contributions of the wind forcing, the surface thermohaline fluxes, the river runoff, and the Bosphorus inflow/outflow in driving the yearly mean circulation in the Black Sea. The model accommodates a topographic and boundary-fitted curvilinear coordinate system and resolves steep topographical changes around the periphery of the basin using O(10 km) grid spacing and 18 stretched vertical levels. Model experiments show that topography, wind forcing, and buoyancy forcing are all first-order contributors to the primary circulation of the Black Sea. If any of these features are neglected, significant elements of the model circulation do not reproduce observations. Subbasin scale gyres are caused by both wind and thermohaline forcing. Annual mean wind stress is sufficient to produce the major interior cyclonic gyres. Stronger winds produce more defined interior flow than the weaker winds of the Hellermann and Rosenstein (1983) fields. Heat flux is an important contributor to subbasin scale cyclonic circulation. However, the annual mean heat flux with spatial structure given by the climatology produces unrealistic features in the interior circulation. The latter ones disappear when including the seasonal heat flux variability. This results strongly suggests that the seasonal cycle of the wind stress is much less crucial than the heat flux seasonal cycle in producing a realistic basin circulation. The Rim Current is locked to the steep topographic shelf slope, regardless of the forcing mechanism. Without including the strong topography the Rim Current is absent for all forcings. Mesoscale variability arises from the dynamic evolution of the Rim Current. This variability is enhanced by the Danube inflow and the Bosphorus inflow/outflow, demonstrating the importance of these buoyancy sources in enhancing the mesoscale. The deep-layer circulation is controlled by the barotropic pressure gradient and is insensitive to the magnitude, seasonality, or strength of the surface forcing. A transition zone separates the surface and deep-layer circulation patterns. Its circulation is mainly driven by the slope of the pycnocline developed as a response to the surface forcing.

Wind and thermohaline circulation of the Black Sea driven by yearly mean climatological forcing

It has been observed that storms in early fall can result in top-to-bottom mixing of Chesapeake Bay. A three-dimensional, time-dependent circulation model is used to examine this destratification process for September 1983, when extensive current and hydrographic data were available. The model bay is forced at the surface by observed hourly winds, at the ocean boundary by observed hourly surface and bottom salinities and sea level fluctuations, and at the head by observed daily discharges for a 28-d period. A second-moment, turbulence-closure submodel, with no adjustments from previous applications to its requisite coefficients, is used to calculate the vertical turbulence mixing coefficients. Comparisons with data inside the model domain indicate relative errors of 7% to 14% for sea level, 7% to 35% for current, and 11% to 21% for salinity. The tidal portion of the spectrum is modeled better than the subtidal portion. The model is used to examine both the mechanisms of wind mixing and the temporal and spatial distribution of vertical mixing within the estuary. Wind-driven internal shear is shown to be a more effective mechanism of inducing destratification than turbulence generated at the surface. The model is also used to show that the vertical temperature inversion which occurs in the fall does not affect the timing of the destratification as much as its completeness. The distribution of mid-depth vertical mixing shows highly variable values in the mid-bay region, where wind-induced mixing is dominant. This suggests that the source of oxygen to mid-bay bottom waters is similarly variable. Vertical turbulence mixing coefficients of 10−2 cm2 s−1 (background) to 103 cm2 s−1 were needed to simulate the September period, indicating the need for time-variable mixing in models of dissolved and suspended estuarine constituents.

Modeling of wind-induced destratification in Chesapeake Bay

Circulation Modelling using Orthogonal Curvilinear Coordinates

Northern Gulf of Mexico Littoral Initiative Modeling Program

A three-dimensional circulation model has been developed using an orthogonal curvilinear coordinate system. The model as constructed is capable of simulations on a variety of time and space scales of currents and sea surface elevations in estuaries and in coastal waters within a few hundred kilometers of the coast as well as for entire ocean basins. The governing equations, cast into curvilinear coordinates, are solved using standard finite difference techniques which accommodate irregularly shaped, but orthogonal, computational grids. A simulation of California Current System is presented. The paper concludes with a discussion of a rather efficient grid encompassing the Mid-Atlantic Bight, the Gulf of Maine and the Bay of Fundy.

H. James Herring

Papers

Circulation Modelling using Orthogonal Curvilinear Coordinates

Northern Gulf of Mexico Littoral Initiative Modeling Program

3-D Orthogonal Curvilinear Circulation Modelling