Resonant inertial oscillations in moored buoy ocean surface winds

Abstract

The surface winds from the moored buoy data set available from the National Data Buoy Center are examined for the occurrence of inertial range oscillations in the surface winds by employing a novel joint time frequency analysis of the two-component vector winds. This data set was chosen for its high time resolution (1-h sampling) that enabled the full characterization of these inertial oscillations, its at least partially global coverage, and its record length, which is needed to extract the signals from the background noise. The observation system is comprised of over 200 sites with measurements as far back as 1972. Because of the large amount of data, many harmonics of the diurnal atmospheric tidal signature in the surface winds (24, 12, 8, and 3 h) were found in high-precision power spectra. These tidal oscillations are found to be important contributors to the inertial range oscillation at latitudes of 30°, where the largest inertial range oscillations are found. By turning to local (in time) spectral analysis using the S-transform, considerable energy was also found in the inertial frequency ranges at other latitudes, typically in the form of very large (>10 m s—1), yet short-lived (of the order of a few days) events. The surface wind rotation direction in near inertial frequency bands favors resonant inertial oscillations at all latitudes, and in every season of the year.