Regional atmosphere-ocean-ice climate modelling over Eastern Canada

The interactions in the atmosphere-ocean-ice system play an important role for the climate of Eastern Canada because of the presence of the North Atlantic Ocean, the Labrador Sea, the Gulf of St-Lawrence, Hudson Bay and the Great Lakes. These basins form a complex coastline that contributes to the interactions with the atmosphere. However, the interactions and their role on the climate of Eastern Canada are still poorly understood. Coupled general circulation models (GCMs) around the world have been used to gain knowledge of the atmosphere-ocean-ice interactions. However, these models do not have a resolution fine enough to resolve the small-scale interactions of the Eastern Canada area. Therefore, we use the Canadian Regional Climate Model (CRCM) developed at the “Université du Québec à Montréal” and a regional ocean-ice model for the Gulf of St. Lawrence and its estuary (GOM) developed at the Institute of Maurice Lamontagne, Qc. Canada to understand the interactions between the atmosphere, the ocean and the sea-ice in the Gulf of St.-Lawrence. The Gulf of St. Lawrence is unique because it is a semi-enclosed basin, relatively shallow and largely dominated by atmospheric forcing and fresh water fluxes. In winter, the combined effect of the tide and winds may produce ice motion up to 5cm s-1 opening leads that can locally induce fluxes of sensible heat up to 1000 w m-2. These characteristics are in contrast to open shelf areas of Canada where ocean properties are largely controlled by offshore ocean circulation. By resolving details in the SST and ice fields, the surface heat fluxes, convective precipitation and mesoscale circulation patterns may be significantly modified.

While the problem of coupling global atmospheric and oceanic models has been addressed for some time, coupling regional atmospheric and oceanic models is still in its infancy. Coupling of atmospheric and oceanic models is mainly a problem of exchange of momentum, heat and fresh water between the two systems via fluxes of these quantities at the interface. These fluxes control the climate of both the ocean surface layer and the overlying atmosphere. Because of simplifications, inadequacies or limitations of the formulation the models and the interface linking them, an analysis of the surface fluxes is performed to evaluate the degree of balance of the interacting components. The study period is from December 1989 to March 1990 with 2 months of spinup. The period was chosen because the air temperature over Eastern Canada was relatively cold at the beginning, enhancing the exchange between the atmosphere and the ocean, and the ice formation in the Gulf of St.-Lawrence was higher than normal.