Global estimates of the energy transfer from the wind to the ocean, with emphasis on near-inertial oscillations

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(8), (2019): 5723-5746, doi:10.1029/2018JC014453.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‐Range Weather 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.We thank three anonymous reviewers for their helpful comments that led to an improved manuscript. We are grateful to Jörn Callies and Laurie Padman for fruitful discussions. This work is funded by the National Aeronautics and Space Administration (NASA) through the project “Towards improved estimates of upper ocean energetics: Science motivation for the simultaneous measurement of ocean surface vector winds and currents” (Grant NNX15AG42G) and through NASA Grant NNX14AM71G and NNX16AH76G. Model output from global 1/48° and 1/24° ECCO2 MITgcm simulations is freely available to the community. For access of the full solutions, we recommend that users apply for an HEC account at NASA Ames. Data are provided online (∼dmenemen/llc/). Users without a NASA Ames account may explore what is available online (https://data.nas.nasa.gov/ecco/). This work was, in part, performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Color maps used in this contribution are from Thyng et al. (2016). To Teresa and Francesc, for their patience