An upper ocean current jet and internal waves in a Gulf Stream warm core ring

On June 22, 1982, the R/V Endeavor, while participating in a multi-ship study of a warm core ring 82B, encountered a strong front in the core of the ring. The vessel was headed on a radial section outward from ring center while a CTD was repeatedly raised and lowered between 10 and 300 m. Current profiles in the upper 100 m were obtained continuously with a Doppler acoustic profiling system. Above the shallow 45 m seasonal thermocline, a current jet of 4 km width was encountered having a central core of relatively light water and a maximum current of 1.1 m/s. This jet was both highly nonlinear and totally unexpected. A high frequency packet of directional internal waves was acoustically observed in the seasonal thermocline at the outer edge of the jet. Vertical velocities were large enough (6 cm/s) as to be directly observable in the Doppler returns. The waves were propagating from the northeast, parallel to the ship track, and orthogonal to the jet toward the center of the warm core ring. While a nonlinear, centrifugal term was required for the force balance of the jet, the high-frequency internal wave packet could be explained with linear, gravest-mode wave dynamics.