Contribution of inertia in mesoscale eddies when deriving ocean currents from sea surface height.

An ocean circulation model shows a significant contribution of advective terms in the surface momentum balance of Mozambique channel rings. Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH): gradient wind, perturbation expansion, and an iterative method.They are tested in a model and applied to satellite altimetry.

In the central Mozambique channel, the error RMS in surface velocities based on 8 years of model SSH is in excess of 30 cm s-1for geostrophy and reduces to about 10 cm s-1 for the gradient wind and iterative methods. The perturbation method is less accurate. Applied to satellite altimetry, the addition of inertia results in a significant increase in velocities for the anticyclones and a decrease for the cyclones. It induces a velocity increase in excess of 50% in Mozambique Channel rings.

Theses methods are applied over the global ocean. They confirm the hypothesis that centrifugal accelerations are responsible for the difference between geostrophic and drifter eddy kinetic energies in the Gulf Stream.