Coupled Modeling of the North Atlantic / Gulf of Maine System Dale Haidvogel

Dale Haidvogel, Mohamed Iskandarani, and Julia Levin

We wish to assess the importance of remote physical forcing on Georges Bank. To do so, we are coupling the Dartmouth Georges Bank / Gulf of Maine model to a basin-scale model of the North Atlantic developed at Rutgers. Though differing somewhat in specific approach (QUODDY uses low-order triangles, SEOM uses high-order quadrilaterals), both are Galerkin-based finite element models for which prior coupling strategies have been developed.

In view of the numerical and dynamical complexities involved, model coupling will proceed in stages. As a first step, we are preparing for a series of simulations in which only barotropic coupling is allowed. External forcing mechanisms to be explored in this first phase include (the depth-integrated influences of) the wind-driven circulation, mesoscale eddies and rings, and tides. Full 3D coupling will be undertaken in a second phase.

In order to expedite model coupling, we have produced a two-layer version of the North Atlantic model. The two-layer version has the advantage of being mathematically simple and computationally fast, while retaining the rudiments of important baroclinic and barotropic processes, e.g., tides, sheared wind-driven currents, baroclinic instability. This fast version of the basin-scale model will be used to efficiently prototype the coupling algorithms.

Here, we review the current status of the basin-scale simulations, and discuss our coupling strategy. Important issues that are still pending include:

  1. Coupling (mortar element coupling or flux coupling via characteristics?)
  2. Treatment of topography (topographic ranges where the two models will meet?)
  3. Mesoscale processes (how soon should we undertake eddy-resolving simulations in the basin-scale model?)