Reconstructing ocean surface momentum conservation from altimetry, drifters and wind reanalysis

Improving our understanding and ability to represent surface oceanic dynamics is crucial for the study and forecast of the climate system, as it modulates air-sea interactions and marine ecosystem. 

The recently launched SWOT altimetric satellite is providing a 2D highly resolved vision of sea level (down to submesoscales) and may thus offer a brand new view on upper ocean circulation.

If geostrophy has historically allowed a global estimation of mesoscale and larger ocean surface circulation from classical altimetry, it is jeopardized at the scales resolved by SWOT by contributions from higher frequency processes such as internal tides, near-inertial waves and wind effect.

Drifters trajectories, which provide a high frequency  'ground-truth’ estimate of the upper ocean circulation and wind reanalysis products are thus highly complementary to altimetry to reconstruct surface ocean dynamic. 

The horizontal surface momentum conservation is here reconstructed from historical altimetric data, drifters derived currents (Global Drifter Program) and atmospheric reanalysis products. We will present our ability at closing upper ocean momentum balance globally and quantify contributions from different terms involved (inertial acceleration, coriolis acceleration, pressure gradient and wind stress vertical divergence). This will allow to qualify and map the dominant dynamical balances, revealing the limit of geostrophy and the dominance of inertial balance in some areas. An error budget is also estimated.