Atmosphere-ocean-ice interaction processes in the Gulf of St. Lawrence: numerical study with a coupled model

A 15-km version of the Canadian Regional Climate Model has been coupled with the 3D ocean-ice model of the Gulf of St. Lawrence (GSL) to study air-sea interaction processes during two wintertime atmospheric cyclonic events over northeastern Canada. In the context of low-level cold air advection over this region, we focus on the effects of these interactive processes both on the upper ocean mixed layer of the GSL and on the regional atmospheric circulation. Two simulations are realized for the first week of January 1990, first with an off-line coupling (every 24 hours) between oceanic and atmospheric models, and second with fixed oceanic conditions during the period of integration. This winter period in the GSL is generally associated with rapid sea ice cover growth, rapid seawater cooling, and large interannual variability in the sea ice cover. These simulations are conducted under global analysis fields at coarse resolution through multiple nesting of the atmospheric model, from 60 km horizontal resolution to 30 and then 15 km. The ice-ocean conditions on the Labrador Shelf were kept identical in the two runs. The comparison between the two simulations shows that the changes in oceanic heat flux due to the changes in the ice cover have a significant effect on the near surface state of the atmosphere in both the Gulf and the Labrador Sea. The results show that atmosphere/ocean feedbacks in the Gulf directly can affect surface heat loss and sea ice growth in the Labrador Shelf, and sea level pressure variability in the northwestern Atlantic. We also examine the evolution of upper ocean in the GSL due to cold air outbreak and the mesoscale atmospheric flow pattern induced by air-sea fluxes. We also show that the increased wind resolution from 30 to 15 km modifies the drift and concentration of the sea ice in the GSL. Finally, the results suggest that the daily changes in sea ice conditions in the Gulf have an important impact on numerical simulation in the northwestern Atlantic region.