Internal wave variability in the Beaufort Sea during the winter of 1993/1994

Acoustic Doppler current profiler observations were obtained at the Sea Ice Mechanics Initiative Ice Camp as it drifted through the Beaufort Sea over the winter of 1993-1994. In this paper, the variability of the internal wave field is examined. Initially (December 1993-January 1994), the camp drifted westward through the central Canada Basin (75degreesN, 139degrees-153degreesW). Numerous anticyclonic baroclinic eddies were encountered. Internal wave energy levels averaged 1/25 of the Garrett-Munk (GM) standard. Shear variance averaged 1/17 GM. During February-March 1994, the camp drifted meridionally along 156degreesW (near the Northwind Ridge), reversing direction several times. Large baroclinic vortices were not detected. Internal wave energy levels were significantly greater during this period, peaking at 1/6 GM. Shear variance peaked at 1/3 GM. The waves were predominantly near inertial, resulting from three distinct surface generation events. Downward vertical energy fluxes ranged from typical values of 0.02 mW/m(2) to a peak value of 0.15 mW/m(2). Two thirds of the downward flux was associated with waves of vertical scale greater than 55 m; the remainder with smaller-scale waves. Upward energy fluxes ranged from 0.02 mW/m(2) (typical) to 0.10 mW/m(2) (peak), supported almost entirely by the larger-scale waves. High ice-water relative velocities (atmospheric storms), accompanied by ice deformation, appear to be necessary, but not sufficient, to assure a downward propagating wave generation event. The highly variable mesoscale has a significant effect on the near-inertial wave field propagation. The data suggest that the vertical propagation of near-inertial waves is strongly affected by the depth variation of the vertical component of mesoscale vorticity. The large Beaufort Sea vortices appear to have a dual effect on the wave field. Enhanced vertical propagation speed (and decreased energy density) is found in the negative vorticity cores. Propagation into the positive vorticity regions surrounding the cores is inhibited. The increase in wave energy experienced as the ice camp left the central Beaufort Sea is jointly associated with the passage of storms and the absence of large baroclinic vortices over the Northwind Ridge.