Global climatology of near-inertial current characteristics from Lagrangian observations

Satellite-tracked surface drifter data from 1999-2006 are used to compute global climatology of inertial current characteristics at seasonal scales. The global mean near-inertial current amplitude at 15m depth is similar to 10 cm s(-1) corresponding to mixed-layer inertial energies of similar to 300 Jm(-2). The Southern Ocean and the western North Pacific and Atlantic oceans are the most energetic in the near-inertial frequency band, whereas weaker inertial activity is observed in the subtropical and eastern boundary regions. In every ocean basin, inertial activity is higher during fall and winter, associated with maximum storms activity and deeper mixed-layers. This study also shows that the mixed-layer model developed by R. T. Pollard and R. C. Millard (1970) and forced by the QSCAT/NCEP blended wind product is too energetic in the tropics and not enough at high latitudes. These discrepancies could question the previous estimates of the wind work to inertial motions based on those simulations.