Sensitivity of the North Atlantic circulation to momentum forcing using a SPEM model

Model simulations are used to investigate the sensitivity of a primitive equation model of the North Atlantic to several wind stress seasonal climatologies. The model is forced with the 40-year climatology of surface wind stress, heat and freshwater fluxes from the NCEP/NCAR re-analysis to provide a simulation of reference. Three tests are carried-out with different wind stress climatologies derived from COADS (1990-1994), using different formulations to estimate the wind stress from ship reports. Another case is carried-out with the climatological wind stress obtained from ERS-1&2 Scatterometer observations (1991-1998). The authors address the amplitude of the Meridional Overturning Cell (MOC) and heat transport (MHT) with respect to the different wind forcings. NCEP winds are found to produce the lowest MHT in relation to less dense water formation at high latitude in winter. Differences in the large-scale circulation patterns are examined, and large differences are found between cases in the Subtropical Gyre (STG) and Subpolar Gyre (SPG), NCEP winds driving the most energetic circulation.