TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 58 (No. 5), pp. 673-682, 2002

Evidence for the Trapping and Amplification of Near- Inertial Motions in a Large Anticyclonic Ring in the Oyashio

Konstantin A. Rogachev1* and Eddy C. Carmack2

1Pacific Oceanological Institute, 43 Baltiyskay Road, Vladivostok 690041, Russia
2Institute of Ocean Sciences, Fisheries and Oceans Canada, Sidney, B.C., V8L 4B2, Canada

(Received 16 November 2001; in revised form 22 March 2002; accepted 22 March 2002)

Abstract: Three ARGOS drift buoys were deployed in the Oyashio Current off the Kuril Islands near 45°N in fall, 1990, during a joint Russia/Canada study of western boundary current dynamics in the Subarctic Pacific Ocean. We here report on one buoy deployed within an anticyclonic warm core ring (WCR86B) which shows evidence of large amplitude inertial motions of near-diurnal frequency. During its first week within the ring the buoy drifted with a mean azimuthal current speed of 0.40-0.45 m s-1 and a radius of rotation of 15-20 km. However, superimposed on the mean rotation of the ring at this time were "loops" of near-diurnal period, radius 7-8 km and speeds exceeding 1 m s-1. During successive rotations the buoy spiraled outward, its mean period of rotation increased and the amplitude of the near-diurnal motions decreased. The large motions are explained by inertial wave trapping and amplification within the extremely large and weakly stratified eddy, wherein the negative vorticity of the eddy reduces the local inertial frequency to near-diurnal frequency. We here suggest that either tidal or wind forcing may generate these high-amplitude "loop" motions.

*Corresponding author E-mail: rogachev@poi.dvo.ru

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