Observations of high-frequency internal waves in the Coastal Ocean Dynamics Region

Abstract

Current meter data from the second Coastal Ocean Dynamics Experiment (CODE II) for July 1982 are analyzed for internal waves in the 6 to 40 cycles per day (cpd) frequency band. It is found that the wave field is anisotropic and that the current ellipses are oriented in approximately the cross-isobath direction. The squares of the ratio of the major to minor axes of the current ellipses (the "ellipticity") are consistent with a continuum of internal waves propagating onshore but are not consistent with a single wave propagating onshore. The reduction of internal wave energy across the shelf is consistent with propagation from the deep ocean or shelf break, as is the correlation between vertical velocities and velocities parallel to the minor axis. However, there is evidence for the generation of additional internal wave energy on the shelf in the evolution of the current ellipses across the shelf and in the bluing of the internal wave spectra across the shelf. Internal wave energy levels are elevated by a factor of 1.5 to 5 above Garrett and Munk [1972] levels at the moorings on the 130 and 365 m isobaths. The first vertical mode dominates at the 130 m isobath, the only mooring for which the vertical modal analysis was done. Copyright 1999 by the American Geophysical Union.