Numerical Simulation of the North Atlantic Ocean at 1/10°

Abstract

In this paper an initial analysis of an 0.1° simulation of the North Atlantic Ocean using a level-coordinate ocean general circulation model forced with realistic winds covering the period 1985?96 is presented. Results are compared to the North Atlantic sector of a global 0.28° simulation with similar surface forcing and to a variety of satellite and in situ observations. The simulation shows substantial improvements in both the eddy variability and the time-mean circulation compared to previous eddy-permitting simulations with resolutions in the range of 1/2°?1/6°. The resolution is finer than the zonal-mean first baroclinic mode Rossby radius at all latitudes, and the model appears to be capturing the bulk of the spectrum of mesoscale energy. The eddy kinetic energy constitutes 70% of the total basin-averaged kinetic energy. Model results agree well with observations of the magnitude and geographical distribution of eddy kinetic energy and sea-surface height variability, with the wavenumber?frequency spectrum of surface height anomalies in the Gulf Stream, with estimates of the eddy length scale as a function of latitude, and with measurements of eddy kinetic energy as a function of depth in the eastern basin. The mean circulation also shows significant improvements compared to previous models, although there are notable remaining discrepancies with observations in some areas. The Gulf Stream separates at Cape Hatteras, and its speed and cross-stream structure are in good agreement with current meter data; however, its path is somewhat too far south and its meander envelope too broad to the west of the New England Seamounts. The North Atlantic Current is remarkably well simulated in the model: it exhibits meanders and troughs in its time-mean path that agree with similar structures seen in float data, although the separation of this current in the region of the ?Northwest Corner? is displaced somewhat too far to the northwest. The Azores Current appears in the simulation, perhaps for the first time in a basin-scale model, and its position, total transport, and eddy variability are consistent with observational estimates.