What is Required to Model the Global Ocean Circulation

Abstract : Simulating and forecasting the circulation of the global ocean is a difficult task. The present generation of high-resolution ocean circulation models, with horizontal resolution of 1/10, appears to be deficient in kinetic energy when compared with long-term observations. A series of near-twin experiments, using the global HYbrid Coordinate Ocean Model (HYCOM) with identical atmospheric forcing, but varying in horizontal resolution and assimilation of altimetric steric height anomalies, show significant improvement with a better representation of mesoscale eddies when compared to observations. For a 1/12.5 (9 km) global model, the eddy kinetic energy (EKE) at the surface and abyss is low by 21% and 24%, respectively, compared to surface drifting buoys and deep current meters. Increasing the model resolution to 1/25 (4.4 km) or injecting mesoscale eddies through the assimilation of surface observations in a 1/12.5 model increases the surface and abyssal EKE to levels consistent with observations.