Global Estimates of the Energy Transfer From the Wind to the Ocean, With Emphasis on Near-Inertial Oscillations

Mar M. Flexas1, Andrew F Thompson2, Hector S Torres3, Patrice Klein3, J. Thomas Farrar4, Hong Zhang5 and Dimitris Menemenlis6, (1)California Institute of Technology, Pasadena, CA, United States, (2)California Institute of Technology, Pasadena, United States, (3)JPL/NASA/Caltech, Pasadena, CA, United States, (4)Woods Hole Oceanographic Inst, Department of Physical Oceanography, Woods Hole, MA, United States, (5)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (6)NASA Jet Propulsion Laboratory, Pasadena, United States
Abstract:
Estimates of the kinetic energy transfer from the wind to the ocean are often limited by the
spatial and temporal resolution of surface currents and surface winds. Here we examine the wind work
in a pair of global, very high-resolution (1/48◦ and 1/24◦) MIT general circulation model simulations in
Latitude-Longitude-polar Cap (LLC) configuration that provide hourly output at spatial resolutions
of a few kilometers and include tidal forcing. A cospectrum analysis of wind stress and ocean surface
currents shows positive contribution at large scales (>300 km) and near-inertial frequency and negative
contribution from mesoscales, tidal frequencies, and internal gravity waves. Larger surface kinetic energy
fluxes are in the Kuroshio in winter at large scales (40 mW/m2) and mesoscales (−30 mW/m2). The
Kerguelen region is dominated by large scale (∼20 mW/m2), followed by inertial oscillations in summer
(13 mW/m2) and mesoscale in winter (−12 mW/m2). Kinetic energy fluxes from internal gravity waves
(−0.1 to −9.9 mW/m2) are generally stronger in summer. Surface kinetic energy fluxes in the LLC
simulations are 4.71 TW, which is 25–85% higher than previous global estimates from coarser (1/6–1/10◦)
general ocean circulation models; this is likely due to improved representation of wind variability
(6-hourly, 0.14◦, operational European Center for Medium-RangeWeather Forecasts). However, the low
wind power input to the near-inertial frequency band obtained with LLC (0.16 TW) compared to global
slab models suggests that wind variability on time scales less than 6 hr and spatial scales less than 15 km
are critical to better representing the wind power input in ocean circulation models.