Atlantic Shelf Circulation Modelling

Quantitative representations of shelf currents are being developed using 3-d numerical hydrodynamics models and observational data. The models, initially developed by and being extended in collaboration with US GLOBEC colleagues, use variable-size finite-element meshes which allow high resolution of key areas such as banks as well as shelf-wide coverage.

Initial applications used diagnostic models (Lynch et al. 1992; Lynch and Naimie 1993) to evaluate the climatological seasonal-mean circulation associated with density, wind and tidal forcing, and the semidiurnal tidal currents. For descriptions of these applications:

• for seasonal circulation on Georges Bank, see Naimie et al. (1994) ;
• for seasonal circulation in the Scotia-Maine region, see Hannah et al. (1996b) ;
• for seasonal circulation on the Scotian Shelf, see Loder et al. (1997a) and Han et al. (1997);
• for seasonal circulation in the Laurentian Channel region, see Han et al. (1999);
• for tidal currents on the Newfoundland and southern Labrador Shelves, see Xu et al. (1999);
• for circulation on the larger-scale Atlantic Shelf, see Hannah et al. (1995a) and Greenberg et al. (1998).

The prognostic advanced-turbulence model QUODDY (Lynch et al. 1996; Naimie 1996) is being used to obtain improved seasonal and tidal circulation fields, with effort to date (at BIO) focussed on the Scotian Shelf and Georges Bank regions. For descriptions of these applications:

• for seasonal circulation on the central and western Scotian Shelf, see Hannah et al. (2001) and Shore et al. (2000) ;
• for decadal-scale circulation changes in the Scotia-Maine region, see Loder et al. (2001c) ;
• for seasonal circulation on the eastern Scotian Shelf, see Han and Loder 1998 .

Methodological extensions led by BIO scientists include:

• a spherical polar version of the linear diagnostic model for basin-scale applications (Greenberg et al. 1998);
• a direct inverse method for open boundary conditions in the linear diagnostic model (Xu 1998, Xu et al. 1999);
• improved representation of the vertical structure of near-surface flow ( Hannah et al. 1999 ).

The models are forced and evaluated using historical datasets for wind stress, density and currents. These datasets have been supplemented by additional field measurements in key areas such as in the Georges Bank Frontal Study. For an overview of this study, see Loder et al. (1993). For a comparison of model and observed turbulence fields, see Horne et al. (1996).

Example Images and Animations
.	Mesh	Topo	Currents			Transp Strmln	Sections
			NrSrf	MdDep	DpAvg
Georges Bank	Refer to Dartmouth College Homepage.
Summer Tidal+Mean
Decadal Change in Winter
Scotian Shelf
Winter Mean
Spring Mean
Summer Mean
Western/Central Scotian Shelf
Winter Mean
Summer Mean
Browns Bank Spring Mean
Sable Is. Bank Spring Mean
Decadal Change in Winter
Gully
Velocity Fields
Particle Trajectories: Winter
Particle Trajectories: Summer
Laurentian Channel
Seasonal Baroclinic
Newfoundland Shelf
Spring Baroclinic
Summer Baroclinic
NW Atlantic Shelf
Barotropic Inflow

• Topo = Topography
• NrSrf = Near-Surface
• MdDep = Middle-Depth
• DpAvg = Depth-Averaged
• Transp Strmln = Transport Streamlines