Internal Swell Generation: The Spatial Distribution of Energy Flux from the Wind to Mixed Layer Near-Inertial Motions

Abstract

The energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50°S to 50°N for the years 1996–99. The wind stress, τ, is computed from 6-h, 2.5°-resolution NCEP–NCAR global reanalysis surface winds. The inertial mixed layer response, u_I, and the energy flux, Π = τ · u_I, are computed using a slab model. The validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and ADCP velocity records from NDBC buoys. (At latitudes > 50°, the inertial response is too fast to be resolved by the reanalysis wind 6-h output interval.) Midlatitude storms produce the greatest fluxes, resulting in broad maxima near 40° latitude during each hemisphere's winter, concentrated in the western portion of each basin. Northern Hemisphere fluxes exceed those in the Southern Hemisphere by about 50%. The global mean energy flux from 1996 to 1999 and 50°S to 50°N is (0.98 ± 0.08) × 10⁻³ W m⁻², for a total power of 0.29 TW (1 TW = 10¹² W). This total is the same order of magnitude as recent estimates of the global power input to baroclinic M₂ tidal motions, suggesting that wind-generated near-inertial waves may play an important role in the global energy balance.