Satellite‐tracked drift buoy observations of the near‐surface flow in the eastern mid‐latitude North Pacific

Abstract

The surface and near‐surface (30 m) currents of the eastern mid‐latitude Pacific obtained from 32 satellite‐tracked drifting buoys during the period June 1976 through August 1977 are discussed. These observations of oceanic currents are merged with and are compared to Fleet Numerical Weather Center's daily estimates of surface winds for the same period. Statistical comparisons of these data sets reveal that the drifters move systematically approximately 30° to the right of the surface wind at approximately 1.5% of the wind speed. This relationship between drifter movement and surface winds occurs during the entire period except for the summer months of 1976 when independent of the surface winds the buoy trajectories indicate mesoscale eddy motions with 100 km and 30 day time and space scales, respectively. Drifter liftimes exceeded that of the 9‐m diameter parachute drogues set at 30 m depth, thus enabling a comparison of the currents derived from the drifter motions at the surface and 30 m. These comparisons reveal no systematic difference in the drifter motions with and without drogues. These results suggest a rather uniform flow in the upper 30 m during periods of steady winds. The estimates of the nature of near‐surface currents obtained from the drifters differ from those predicted by Ekman's classical theory of wind‐driven flow, in that there is no evidence of either a reduction in speed or change in direction of the currents over the upper 30 m.

Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific

“…Current velocities determined from 5-year seasonal averages of surface drifter data (available from Fisheries and Oceans Canada) were found to be 6 ± 4 for the February cruises, 4 ± 2 for the June cruises, and 5 ± 3 cm s −1 for the August cruise. These values agree well with the ∼ 10 cm s −1 value reported by McNally (1981) and used by . Given that the currents in the region generally flow west-east, and with no data at stations north and south of Line P, the north-south transport of 234 Th by advection had to be assumed to be negligible.…”

Large-Scale Air-Sea Interactions and Short-Period Climatic Fluctuations

“…The connection between the mid-latitudinal ocean and the wind is shown from the paths of satellite-tracked drift buoys deployed in the North Pacific as part of the NORPAX study (34,35). The buoys were monitored between the summers of 1976 and 1977.…”

Observed near‐surface currents under high wind speeds

“…The Stokes drift contributes to the surface current typically with a quadratic function of the wind speed when estimated from realistic wave spectra [ Ardhuin et al , 2009]. From previous laboratory experiments and field observations, the surface drift speed is represented by a percentage ( r ) of the wind speed (called surface drift ratio here), varying between 1.5% and 4.1%, with a surface drift angle ( α s ), changing between 0° and 34° to the right of the wind direction in the northern hemisphere [ Wu , 1968; McNally , 1981; Wu , 1983; Peterson , 1985; Brown , 1991].…”